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Dagva O, Thibessard A, Lorenzi JN, Labat V, Piotrowski E, Rouhier N, Myllykallio H, Leblond P, Bertrand C. Correction of non-random mutational biases along a linear bacterial chromosome by the mismatch repair endonuclease NucS. Nucleic Acids Res 2024; 52:5033-5047. [PMID: 38444149 PMCID: PMC11109965 DOI: 10.1093/nar/gkae132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/19/2024] [Accepted: 02/09/2024] [Indexed: 03/07/2024] Open
Abstract
The linear chromosome of Streptomyces exhibits a highly compartmentalized structure with a conserved central region flanked by variable arms. As double strand break (DSB) repair mechanisms play a crucial role in shaping the genome plasticity of Streptomyces, we investigated the role of EndoMS/NucS, a recently characterized endonuclease involved in a non-canonical mismatch repair (MMR) mechanism in archaea and actinobacteria, that singularly corrects mismatches by creating a DSB. We showed that Streptomyces mutants lacking NucS display a marked colonial phenotype and a drastic increase in spontaneous mutation rate. In vitro biochemical assays revealed that NucS cooperates with the replication clamp to efficiently cleave G/T, G/G and T/T mismatched DNA by producing DSBs. These findings are consistent with the transition-shifted mutational spectrum observed in the mutant strains and reveal that NucS-dependent MMR specific task is to eliminate G/T mismatches generated by the DNA polymerase during replication. Interestingly, our data unveil a crescent-shaped distribution of the transition frequency from the replication origin towards the chromosomal ends, shedding light on a possible link between NucS-mediated DSBs and Streptomyces genome evolution.
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Affiliation(s)
- Oyut Dagva
- Université de Lorraine, INRAE, UMR 1128 DynAMic, 54000 Nancy, France
| | | | | | - Victor Labat
- Université de Lorraine, INRAE, UMR 1128 DynAMic, 54000 Nancy, France
| | - Emilie Piotrowski
- Université de Lorraine, INRAE, UMR 1128 DynAMic, 54000 Nancy, France
| | - Nicolas Rouhier
- Université de Lorraine, INRAE, UMR 1136 IAM, 54000 Nancy, France
| | - Hannu Myllykallio
- Ecole Polytechnique, INSERM U696-CNRS UMR 7645 LOB, 91128 Palaiseau, France
| | - Pierre Leblond
- Université de Lorraine, INRAE, UMR 1128 DynAMic, 54000 Nancy, France
| | - Claire Bertrand
- Université de Lorraine, INRAE, UMR 1128 DynAMic, 54000 Nancy, France
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2
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Nickoloff JA, Jaiswal AS, Sharma N, Williamson EA, Tran MT, Arris D, Yang M, Hromas R. Cellular Responses to Widespread DNA Replication Stress. Int J Mol Sci 2023; 24:16903. [PMID: 38069223 PMCID: PMC10707325 DOI: 10.3390/ijms242316903] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 11/22/2023] [Accepted: 11/27/2023] [Indexed: 12/18/2023] Open
Abstract
Replicative DNA polymerases are blocked by nearly all types of DNA damage. The resulting DNA replication stress threatens genome stability. DNA replication stress is also caused by depletion of nucleotide pools, DNA polymerase inhibitors, and DNA sequences or structures that are difficult to replicate. Replication stress triggers complex cellular responses that include cell cycle arrest, replication fork collapse to one-ended DNA double-strand breaks, induction of DNA repair, and programmed cell death after excessive damage. Replication stress caused by specific structures (e.g., G-rich sequences that form G-quadruplexes) is localized but occurs during the S phase of every cell division. This review focuses on cellular responses to widespread stress such as that caused by random DNA damage, DNA polymerase inhibition/nucleotide pool depletion, and R-loops. Another form of global replication stress is seen in cancer cells and is termed oncogenic stress, reflecting dysregulated replication origin firing and/or replication fork progression. Replication stress responses are often dysregulated in cancer cells, and this too contributes to ongoing genome instability that can drive cancer progression. Nucleases play critical roles in replication stress responses, including MUS81, EEPD1, Metnase, CtIP, MRE11, EXO1, DNA2-BLM, SLX1-SLX4, XPF-ERCC1-SLX4, Artemis, XPG, FEN1, and TATDN2. Several of these nucleases cleave branched DNA structures at stressed replication forks to promote repair and restart of these forks. We recently defined roles for EEPD1 in restarting stressed replication forks after oxidative DNA damage, and for TATDN2 in mitigating replication stress caused by R-loop accumulation in BRCA1-defective cells. We also discuss how insights into biological responses to genome-wide replication stress can inform novel cancer treatment strategies that exploit synthetic lethal relationships among replication stress response factors.
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Affiliation(s)
- Jac A. Nickoloff
- Department of Environmental and Radiological Health Sciences, Colorado State University, Ft. Collins, CO 80523, USA
| | - Aruna S. Jaiswal
- Department of Medicine and the Mays Cancer Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; (A.S.J.); (M.T.T.); (R.H.)
| | - Neelam Sharma
- Department of Environmental and Radiological Health Sciences, Colorado State University, Ft. Collins, CO 80523, USA
| | - Elizabeth A. Williamson
- Department of Medicine and the Mays Cancer Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; (A.S.J.); (M.T.T.); (R.H.)
| | - Manh T. Tran
- Department of Medicine and the Mays Cancer Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; (A.S.J.); (M.T.T.); (R.H.)
| | - Dominic Arris
- Department of Medicine and the Mays Cancer Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; (A.S.J.); (M.T.T.); (R.H.)
| | - Ming Yang
- Department of Medicine and the Mays Cancer Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; (A.S.J.); (M.T.T.); (R.H.)
| | - Robert Hromas
- Department of Medicine and the Mays Cancer Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA; (A.S.J.); (M.T.T.); (R.H.)
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3
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Das S, Forrest J, Kuzminov A. Synthetic lethal mutants in Escherichia coli define pathways necessary for survival with RNase H deficiency. J Bacteriol 2023; 205:e0028023. [PMID: 37819120 PMCID: PMC10601623 DOI: 10.1128/jb.00280-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 09/09/2023] [Indexed: 10/13/2023] Open
Abstract
Ribonucleotides frequently contaminate DNA and, if not removed, cause genomic instability. Consequently, all organisms are equipped with RNase H enzymes to remove RNA-DNA hybrids (RDHs). Escherichia coli lacking RNase HI (rnhA) and RNase HII (rnhB) enzymes, the ∆rnhA ∆rnhB double mutant, accumulates RDHs in its DNA. These RDHs can convert into RNA-containing DNA lesions (R-lesions) of unclear nature that compromise genomic stability. The ∆rnhAB double mutant has severe phenotypes, like growth inhibition, replication stress, sensitivity to ultraviolet radiation, SOS induction, increased chromosomal fragmentation, and defects in nucleoid organization. In this study, we found that RNase HI deficiency also alters wild-type levels of DNA supercoiling. Despite these severe chromosomal complications, ∆rnhAB double mutant survives, suggesting that dedicated pathways operate to avoid or repair R-lesions. To identify these pathways, we systematically searched for mutants synthetic lethal (colethal) with the rnhAB defect using an unbiased color screen and a candidate gene approach. We identified both novel and previously reported rnhAB-colethal and -coinhibited mutants, characterized them, and sorted them into avoidance or repair pathways. These mutants operate in various parts of nucleic acid metabolism, including replication fork progression, R-loop prevention and removal, nucleoid organization, tRNA modification, recombinational repair, and chromosome-dimer resolution, demonstrating the pleiotropic nature of RNase H deficiency. IMPORTANCE Ribonucleotides (rNs) are structurally very similar to deoxyribonucleotides. Consequently, rN contamination of DNA is common and pervasive across all domains of life. Failure to remove rNs from DNA has severe consequences, and all organisms are equipped with RNase H enzymes to remove RNA-DNA hybrids. RNase H deficiency leads to complications in bacteria, yeast, and mouse, and diseases like progressive external ophthalmoplegia (mitochondrial defects in RNASEH1) and Aicardi-Goutières syndrome (defects in RNASEH2) in humans. Escherichia coli ∆rnhAB mutant, deficient in RNases H, has severe chromosomal complications. Despite substantial problems, nearly half of the mutant population survives. We have identified novel and previously confirmed pathways in various parts of nucleic acid metabolism that ensure survival with RNase H deficiency.
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Affiliation(s)
- Sneha Das
- Department of Microbiology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Jonathan Forrest
- Department of Microbiology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
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Cox MM, Goodman MF, Keck JL, van Oijen A, Lovett ST, Robinson A. Generation and Repair of Postreplication Gaps in Escherichia coli. Microbiol Mol Biol Rev 2023; 87:e0007822. [PMID: 37212693 PMCID: PMC10304936 DOI: 10.1128/mmbr.00078-22] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/23/2023] Open
Abstract
When replication forks encounter template lesions, one result is lesion skipping, where the stalled DNA polymerase transiently stalls, disengages, and then reinitiates downstream to leave the lesion behind in a postreplication gap. Despite considerable attention in the 6 decades since postreplication gaps were discovered, the mechanisms by which postreplication gaps are generated and repaired remain highly enigmatic. This review focuses on postreplication gap generation and repair in the bacterium Escherichia coli. New information to address the frequency and mechanism of gap generation and new mechanisms for their resolution are described. There are a few instances where the formation of postreplication gaps appears to be programmed into particular genomic locations, where they are triggered by novel genomic elements.
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Affiliation(s)
- Michael M. Cox
- Department of Biochemistry, University of Wisconsin—Madison, Madison, Wisconsin, USA
| | - Myron F. Goodman
- Department of Biological Sciences, University of Southern California, University Park, Los Angeles, California, USA
- Department of Chemistry, University of Southern California, University Park, Los Angeles, California, USA
| | - James L. Keck
- Department of Biological Chemistry, University of Wisconsin—Madison School of Medicine, Madison, Wisconsin, USA
| | - Antoine van Oijen
- Molecular Horizons, University of Wollongong, Wollongong, New South Wales, Australia
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales, Australia
| | - Susan T. Lovett
- Department of Biology, Brandeis University, Waltham, Massachusetts, USA
| | - Andrew Robinson
- Molecular Horizons, University of Wollongong, Wollongong, New South Wales, Australia
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales, Australia
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5
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Zahradka K, Repar J, Đermić D, Zahradka D. Chromosome Segregation and Cell Division Defects in Escherichia coli Recombination Mutants Exposed to Different DNA-Damaging Treatments. Microorganisms 2023; 11:microorganisms11030701. [PMID: 36985274 PMCID: PMC10051365 DOI: 10.3390/microorganisms11030701] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Accepted: 03/05/2023] [Indexed: 03/30/2023] Open
Abstract
Homologous recombination repairs potentially lethal DNA lesions such as double-strand DNA breaks (DSBs) and single-strand DNA gaps (SSGs). In Escherichia coli, DSB repair is initiated by the RecBCD enzyme that resects double-strand DNA ends and loads RecA recombinase to the emerging single-strand (ss) DNA tails. SSG repair is mediated by the RecFOR protein complex that loads RecA onto the ssDNA segment of gaped duplex. In both repair pathways, RecA catalyses reactions of homologous DNA pairing and strand exchange, while RuvABC complex and RecG helicase process recombination intermediates. In this work, we have characterised cytological changes in various recombination mutants of E. coli after three different DNA-damaging treatments: (i) expression of I-SceI endonuclease, (ii) γ-irradiation, and (iii) UV-irradiation. All three treatments caused severe chromosome segregation defects and DNA-less cell formation in the ruvABC, recG, and ruvABC recG mutants. After I-SceI expression and γ-irradiation, this phenotype was efficiently suppressed by the recB mutation, indicating that cytological defects result mostly from incomplete DSB repair. In UV-irradiated cells, the recB mutation abolished cytological defects of recG mutants and also partially suppressed the cytological defects of ruvABC recG mutants. However, neither recB nor recO mutation alone could suppress the cytological defects of UV-irradiated ruvABC mutants. The suppression was achieved only by simultaneous inactivation of the recB and recO genes. Cell survival and microscopic analysis suggest that chromosome segregation defects in UV-irradiated ruvABC mutants largely result from defective processing of stalled replication forks. The results of this study show that chromosome morphology is a valuable marker in genetic analyses of recombinational repair in E. coli.
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Affiliation(s)
- Ksenija Zahradka
- Laboratory for Molecular Microbiology, Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Jelena Repar
- Laboratory for Molecular Microbiology, Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Damir Đermić
- Laboratory for Molecular Microbiology, Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Davor Zahradka
- Laboratory for Molecular Microbiology, Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
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6
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Cory MB, Li A, Hurley CM, Hostetler ZM, Venkatesh Y, Jones CM, Petersson EJ, Kohli RM. Engineered RecA Constructs Reveal the Minimal SOS Activation Complex. Biochemistry 2022; 61:2884-2896. [PMID: 36473084 PMCID: PMC9982712 DOI: 10.1021/acs.biochem.2c00505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The SOS response is a bacterial DNA damage response pathway that has been heavily implicated in bacteria's ability to evolve resistance to antibiotics. Activation of the SOS response is dependent on the interaction between two bacterial proteins, RecA and LexA. RecA acts as a DNA damage sensor by forming lengthy oligomeric filaments (RecA*) along single-stranded DNA (ssDNA) in an ATP-dependent manner. RecA* can then bind to LexA, the repressor of SOS response genes, triggering LexA degradation and leading to induction of the SOS response. Formation of the RecA*-LexA complex therefore serves as the key "SOS activation signal." Given the challenges associated with studying a complex involving multiple macromolecular interactions, the essential constituents of RecA* that allow LexA cleavage are not well defined. Here, we leverage head-to-tail linked and end-capped RecA constructs as tools to define the minimal RecA* filament that can engage LexA. In contrast to previously postulated models, we found that as few as three linked RecA units are capable of ssDNA binding, LexA binding, and LexA cleavage. We further demonstrate that RecA oligomerization alone is insufficient for LexA cleavage, with an obligate requirement for ATP and ssDNA binding to form a competent SOS activation signal with the linked constructs. Our minimal system for RecA* highlights the limitations of prior models for the SOS activation signal and offers a novel tool that can inform efforts to slow acquired antibiotic resistance by targeting the SOS response.
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Affiliation(s)
- Michael B. Cory
- Graduate Group in Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Allen Li
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Christina M. Hurley
- Graduate Group in Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Zachary M. Hostetler
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Yarra Venkatesh
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Chloe M. Jones
- Graduate Group in Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - E. James Petersson
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Rahul M. Kohli
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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7
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Rao TVP, Kuzminov A. Robust linear DNA degradation supports replication-initiation-defective mutants in Escherichia coli. G3 (BETHESDA, MD.) 2022; 12:jkac228. [PMID: 36165702 PMCID: PMC9635670 DOI: 10.1093/g3journal/jkac228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Accepted: 08/22/2022] [Indexed: 06/16/2023]
Abstract
RecBCD helicase/nuclease supports replication fork progress via recombinational repair or linear DNA degradation, explaining recBC mutant synthetic lethality with replication elongation defects. Since replication initiation defects leave chromosomes without replication forks, these should be insensitive to the recBCD status. Surprisingly, we found that both Escherichia coli dnaA46(Ts) and dnaC2(Ts) initiation mutants at semi-permissive temperatures are also recBC-colethal. Interestingly, dnaA46 recBC lethality suppressors suggest underinitiation as the problem, while dnaC2 recBC suppressors signal overintiation. Using genetic and physical approaches, we studied the dnaA46 recBC synthetic lethality, for the possibility that RecBCD participates in replication initiation. Overproduced DnaA46 mutant protein interferes with growth of dnaA+ cells, while the residual viability of the dnaA46 recBC mutant depends on the auxiliary replicative helicase Rep, suggesting replication fork inhibition by the DnaA46 mutant protein. The dnaA46 mutant depends on linear DNA degradation by RecBCD, rather than on recombinational repair. At the same time, the dnaA46 defect also interacts with Holliday junction-moving defects, suggesting reversal of inhibited forks. However, in contrast to all known recBC-colethals, which fragment their chromosomes, the dnaA46 recBC mutant develops no chromosome fragmentation, indicating that its inhibited replication forks are stable. Physical measurements confirm replication inhibition in the dnaA46 mutant shifted to semi-permissive temperatures, both at the level of elongation and initiation, while RecBCD gradually restores elongation and then initiation. We propose that RecBCD-catalyzed resetting of inhibited replication forks allows replication to displace the "sticky" DnaA46(Ts) protein from the chromosomal DNA, mustering enough DnaA for new initiations.
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Affiliation(s)
| | - Andrei Kuzminov
- Corresponding author: Department of Microbiology, University of Illinois at Urbana-Champaign, B103 C&LSL, 601 South Goodwin Avenue, Urbana, IL 61801-3709, USA.
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8
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Mahaseth T, Kuzminov A. Catastrophic chromosome fragmentation probes the nucleoid structure and dynamics in Escherichia coli. Nucleic Acids Res 2022; 50:11013-11027. [PMID: 36243965 PMCID: PMC9638926 DOI: 10.1093/nar/gkac865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 09/14/2022] [Accepted: 09/26/2022] [Indexed: 11/17/2022] Open
Abstract
Escherichia coli cells treated with a combination of cyanide (CN) and hydrogen peroxide (HP) succumb to catastrophic chromosome fragmentation (CCF), detectable in pulsed-field gels as >100 double-strand breaks per genome equivalent. Here we show that CN + HP-induced double-strand breaks are independent of replication and occur uniformly over the chromosome,—therefore we used CCF to probe the nucleoid structure by measuring DNA release from precipitated nucleoids. CCF releases surprisingly little chromosomal DNA from the nucleoid suggesting that: (i) the nucleoid is a single DNA-protein complex with only limited stretches of protein-free DNA and (ii) CN + HP-induced breaks happen within these unsecured DNA stretches, rather than at DNA attachments to the central scaffold. Mutants lacking individual nucleoid-associated proteins (NAPs) release more DNA during CCF, consistent with NAPs anchoring chromosome to the central scaffold (Dps also reduces the number of double-strand breaks directly). Finally, significantly more broken DNA is released once ATP production is restored, with about two-thirds of this ATP-dependent DNA release being due to transcription, suggesting that transcription complexes act as pulleys to move DNA loops. In addition to NAPs, recombinational repair of double-strand breaks also inhibits DNA release by CCF, contributing to a dynamic and complex nucleoid structure.
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Affiliation(s)
- Tulip Mahaseth
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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9
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Khan SR, Kuzminov A. Thymine-starvation-induced chromosomal fragmentation is not required for thymineless death in Escherichia coli. Mol Microbiol 2022; 117:1138-1155. [PMID: 35324030 DOI: 10.1111/mmi.14897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 03/15/2022] [Accepted: 03/16/2022] [Indexed: 11/29/2022]
Abstract
Thymine or thymidine starvation induces robust chromosomal fragmentation in E. coli thyA deoCABD mutants, and is proposed to be the cause of thymineless death (TLD). However, fragmentation kinetics challenges the idea that fragmentation causes TLD, by peaking before the onset of TLD and disappearing by the time TLD accelerates. Quantity and kinetics of fragmentation also stays unchanged in hyper-TLD-exhibiting recBCD mutant, making its faster and deeper TLD independent of fragmentation as well. Elimination of fragmentation without affecting cellular metabolism did not abolish TLD in the thyA mutant, but reduced early TLD in the thyA recBCD mutant, suggesting replication-dependent, but undetectable by pulsed field gel, double-strand breaks contributed to TLD. Chromosomal fragmentation, but not TLD, was eliminated in both the thyA and thyA recBCD mutants harboring deoCABD operon. Expression of a single gene, deoA, encoding thymidine phosphorylase, was sufficient to abolish fragmentation, suggesting thymidine-to-thymine interconversion during T-starvation being a key factor. Overall, this study reveals that chromosomal fragmentation, a direct consequence of T-starvation, is either dispensable or redundant for the overall TLD pathology, including hyper-TLD in the recBCD mutant. Replication forks, unlike chromosomal fragmentation, may provide minor contribution to TLD, but only in the repair-deficient thyA deoCABD recBCD mutant.
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Affiliation(s)
- Sharik R Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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10
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Zannier F, Portero LR, Douki T, Gärtner W, Farías ME, Albarracín VH. Proteomic Signatures of Microbial Adaptation to the Highest Ultraviolet-Irradiation on Earth: Lessons From a Soil Actinobacterium. Front Microbiol 2022; 13:791714. [PMID: 35369494 PMCID: PMC8965627 DOI: 10.3389/fmicb.2022.791714] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Accepted: 01/26/2022] [Indexed: 11/13/2022] Open
Abstract
In the Central Andean region in South America, high-altitude ecosystems (3500-6000 masl) are distributed across Argentina, Chile, Bolivia, and Peru, in which poly-extremophilic microbes thrive under extreme environmental conditions. In particular, in the Puna region, total solar irradiation and UV incidence are the highest on Earth, thus, restraining the physiology of individual microorganisms and the composition of microbial communities. UV-resistance of microbial strains thriving in High-Altitude Andean Lakes was demonstrated and their mechanisms were partially characterized by genomic analysis, biochemical and physiological assays. Then, the existence of a network of physiological and molecular mechanisms triggered by ultraviolet light exposure was hypothesized and called "UV-resistome". It includes some or all of the following subsystems: (i) UV sensing and effective response regulators, (ii) UV-avoidance and shielding strategies, (iii) damage tolerance and oxidative stress response, (iv) energy management and metabolic resetting, and (v) DNA damage repair. Genes involved in the described UV-resistome were recently described in the genome of Nesterenkonia sp. Act20, an actinobacterium which showed survival to high UV-B doses as well as efficient photorepairing capability. The aim of this work was to use a proteomic approach together with photoproduct measurements to help dissecting the molecular events involved in the adaptive response of a model High-Altitude Andean Lakes (HAAL) extremophilic actinobacterium, Nesterenkonia sp. Act20, under artificial UV-B radiation. Our results demonstrate that UV-B exposure induced over-abundance of a well-defined set of proteins while recovery treatments restored the proteomic profiles present before the UV-challenge. The proteins involved in this complex molecular network were categorized within the UV-resistome subsystems: damage tolerance and oxidative stress response, energy management and metabolic resetting, and DNA damage repair.
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Affiliation(s)
- Federico Zannier
- Laboratorio de Microbiología Ultraestructural y Molecular, Centro Integral de Microscopía Electrónica, Facultad de Agronomía y Zootecnia, UNT y Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
- Laboratorio de Investigaciones Microbiológicas de Lagunas Andinas, Planta Piloto de Procesos Industriales y Microbiológicos, Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
| | - Luciano R. Portero
- Laboratorio de Microbiología Ultraestructural y Molecular, Centro Integral de Microscopía Electrónica, Facultad de Agronomía y Zootecnia, UNT y Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
- Laboratorio de Investigaciones Microbiológicas de Lagunas Andinas, Planta Piloto de Procesos Industriales y Microbiológicos, Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
| | - Thierry Douki
- Université Grenoble Alpes, Commissariat a l’Energie Atomique et aux Energies Alternatives, Centre National de la Recherche Scientifique, Institut de Recherche Interdisciplinaire de Grenoble–Systèmes Moléculaires et nanoMatériaux p our l’Énergie et la Santé, Grenoble, France
| | - Wolfgang Gärtner
- Institute of Analytical Chemistry, University of Leipzig, Leipzig, Germany
| | - María E. Farías
- Laboratorio de Microbiología Ultraestructural y Molecular, Centro Integral de Microscopía Electrónica, Facultad de Agronomía y Zootecnia, UNT y Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
| | - Virginia H. Albarracín
- Laboratorio de Microbiología Ultraestructural y Molecular, Centro Integral de Microscopía Electrónica, Facultad de Agronomía y Zootecnia, UNT y Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
- Laboratorio de Investigaciones Microbiológicas de Lagunas Andinas, Planta Piloto de Procesos Industriales y Microbiológicos, Centro Científico Tecnológico, CONICET NOASUR, San Miguel de Tucumán, Argentina
- Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de Tucumán, San Miguel de Tucumán, Argentina
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11
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The rarA gene as part of an expanded RecFOR recombination pathway: Negative epistasis and synthetic lethality with ruvB, recG, and recQ. PLoS Genet 2021; 17:e1009972. [PMID: 34936656 PMCID: PMC8735627 DOI: 10.1371/journal.pgen.1009972] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 01/06/2022] [Accepted: 12/01/2021] [Indexed: 11/19/2022] Open
Abstract
The RarA protein, homologous to human WRNIP1 and yeast MgsA, is a AAA+ ATPase and one of the most highly conserved DNA repair proteins. With an apparent role in the repair of stalled or collapsed replication forks, the molecular function of this protein family remains obscure. Here, we demonstrate that RarA acts in late stages of recombinational DNA repair of post-replication gaps. A deletion of most of the rarA gene, when paired with a deletion of ruvB or ruvC, produces a growth defect, a strong synergistic increase in sensitivity to DNA damaging agents, cell elongation, and an increase in SOS induction. Except for SOS induction, these effects are all suppressed by inactivating recF, recO, or recJ, indicating that RarA, along with RuvB, acts downstream of RecA. SOS induction increases dramatically in a rarA ruvB recF/O triple mutant, suggesting the generation of large amounts of unrepaired ssDNA. The rarA ruvB defects are not suppressed (and in fact slightly increased) by recB inactivation, suggesting RarA acts primarily downstream of RecA in post-replication gaps rather than in double strand break repair. Inactivating rarA, ruvB and recG together is synthetically lethal, an outcome again suppressed by inactivation of recF, recO, or recJ. A rarA ruvB recQ triple deletion mutant is also inviable. Together, the results suggest the existence of multiple pathways, perhaps overlapping, for the resolution or reversal of recombination intermediates created by RecA protein in post-replication gaps within the broader RecF pathway. One of these paths involves RarA.
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Rørvik GH, Naemi A, Edvardsen PKT, Simm R. The c-di-AMP signaling system influences stress tolerance and biofilm formation of Streptococcus mitis. Microbiologyopen 2021; 10:e1203. [PMID: 34459556 PMCID: PMC8289670 DOI: 10.1002/mbo3.1203] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Revised: 05/07/2021] [Accepted: 05/14/2021] [Indexed: 11/16/2022] Open
Abstract
Streptococcus mitis is a commensal bacterial species of the oral cavity, with the potential for opportunistic pathogenesis. For successful colonization, S. mitis must be able to adhere to surfaces of the oral cavity and survive and adapt to frequently changing environmental conditions. Cyclic-di-AMP (c-di-AMP) is a nucleotide second messenger, involved in the regulation of stress responses and biofilm formation in several bacterial species. Cyclic-di-AMP is produced by diadenylate cyclases and degraded by phosphodiesterases. We have previously shown that in S. mitis, one diadenylate cyclase (CdaA) and at least two phosphodiesterases (Pde1 and Pde2) regulate the intracellular concentration of c-di-AMP. In this study, we utilized S. mitis deletion mutants of cdaA, pde1, and pde2 to analyze the role of c-di-AMP signaling in various stress responses, biofilm formation, and adhesion to eukaryotic cells. Here, we demonstrate that the Δpde1 mutant displayed a tendency toward increased susceptibility to acetic acid at pH 4.0. Deletion of cdaA increases auto-aggregation of S. mitis but reduces biofilm formation on an abiotic surface. These phenotypes are more pronounced under acidic extracellular conditions. Inactivation of pde1 or pde2 reduced the tolerance to ciprofloxacin, and UV radiation and the Δpde1 mutant was more susceptible to Triton X-100, indicating a role for c-di-AMP signaling in responses to DNA damage and cell membrane perturbation. Finally, the Δpde2 mutant displayed a tendency toward a reduced ability to adhere to oral keratinocytes. Taken together, our results indicate an important role for c-di-AMP signaling in cellular processes important for colonization of the mouth.
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Affiliation(s)
| | | | - Per Kristian Thorén Edvardsen
- Institute of Oral BiologyUniversity of OsloOsloNorway
- Present address:
Faculty of Chemistry, Biotechnology and Food ScienceNorwegian University of Life SciencesÅsNorway
| | - Roger Simm
- Institute of Oral BiologyUniversity of OsloOsloNorway
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Kouzminova EA, Kuzminov A. Ultraviolet-induced RNA:DNA hybrids interfere with chromosomal DNA synthesis. Nucleic Acids Res 2021; 49:3888-3906. [PMID: 33693789 PMCID: PMC8053090 DOI: 10.1093/nar/gkab147] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 02/14/2021] [Accepted: 02/23/2021] [Indexed: 12/28/2022] Open
Abstract
Ultraviolet (UV) induces pyrimidine dimers (PDs) in DNA and replication-dependent fragmentation in chromosomes. The rnhAB mutants in Escherichia coli, accumulating R-loops and single DNA-rNs, are generally resistant to DNA damage, but are surprisingly UV-sensitive, even though they remove PDs normally, suggesting irreparable chromosome lesions. We show here that the RNase H defect does not cause additional chromosome fragmentation after UV, but inhibits DNA synthesis after replication restart. Genetic analysis implies formation of R-loop-anchored transcription elongation complexes (R-loop-aTECs) in UV-irradiated rnhAB mutants, predicting that their chromosomal DNA will accumulate: (i) RNA:DNA hybrids; (ii) a few slow-to-remove PDs. We confirm both features and also find that both, surprisingly, depend on replication restart. Finally, enriching for the UV-induced RNA:DNA hybrids in the rnhAB uvrA mutants also co-enriches for PDs, showing their co-residence in the same structures. We propose that PD-triggered R-loop-aTECs block head-on replication in RNase H-deficient mutants.
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Affiliation(s)
- Elena A Kouzminova
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Narasimha A, Basu B. New insights into the activation of Radiation Desiccation Response regulon in Deinococcus radiodurans. J Biosci 2021. [DOI: 10.1007/s12038-020-00123-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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15
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Exopolysaccharide defects cause hyper-thymineless death in Escherichia coli via massive loss of chromosomal DNA and cell lysis. Proc Natl Acad Sci U S A 2020; 117:33549-33560. [PMID: 33318216 DOI: 10.1073/pnas.2012254117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Thymineless death in Escherichia coli thyA mutants growing in the absence of thymidine (dT) is preceded by a substantial resistance phase, during which the culture titer remains static, as if the chromosome has to accumulate damage before ultimately failing. Significant chromosomal replication and fragmentation during the resistance phase could provide appropriate sources of this damage. Alternatively, the initial chromosomal replication in thymine (T)-starved cells could reflect a considerable endogenous dT source, making the resistance phase a delay of acute starvation, rather than an integral part of thymineless death. Here we identify such a low-molecular-weight (LMW)-dT source as mostly dTDP-glucose and its derivatives, used to synthesize enterobacterial common antigen (ECA). The thyA mutant, in which dTDP-glucose production is blocked by the rfbA rffH mutations, lacks a LMW-dT pool, the initial DNA synthesis during T-starvation and the resistance phase. Remarkably, the thyA mutant that makes dTDP-glucose and initiates ECA synthesis normally yet cannot complete it due to the rffC defect, maintains a regular LMW-dT pool, but cannot recover dTTP from it, and thus suffers T-hyperstarvation, dying precipitously, completely losing chromosomal DNA and eventually lysing, even without chromosomal replication. At the same time, its ECA+ thyA parent does not lyse during T-starvation, while both the dramatic killing and chromosomal DNA loss in the ECA-deficient thyA mutants precede cell lysis. We conclude that: 1) the significant pool of dTDP-hexoses delays acute T-starvation; 2) T-starvation destabilizes even nonreplicating chromosomes, while T-hyperstarvation destroys them; and 3) beyond the chromosome, T-hyperstarvation also destabilizes the cell envelope.
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Sinha AK, Løbner-Olesen A, Riber L. Bacterial Chromosome Replication and DNA Repair During the Stringent Response. Front Microbiol 2020; 11:582113. [PMID: 32983079 PMCID: PMC7483579 DOI: 10.3389/fmicb.2020.582113] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Accepted: 08/13/2020] [Indexed: 01/23/2023] Open
Abstract
The stringent response regulates bacterial growth rate and is important for cell survival under changing environmental conditions. The effect of the stringent response is pleiotropic, affecting almost all biological processes in the cell including transcriptional downregulation of genes involved in stable RNA synthesis, DNA replication, and metabolic pathways, as well as the upregulation of stress-related genes. In this Review, we discuss how the stringent response affects chromosome replication and DNA repair activities in bacteria. Importantly, we address how accumulation of (p)ppGpp during the stringent response shuts down chromosome replication using highly different strategies in the evolutionary distant Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. Interestingly, (p)ppGpp-mediated replication inhibition occurs downstream of the origin in B. subtilis, whereas replication inhibition in E. coli takes place at the initiation level, suggesting that stringent cell cycle arrest acts at different phases of the replication cycle between E. coli and B. subtilis. Furthermore, we address the role of (p)ppGpp in facilitating DNA repair activities and cell survival during exposure to UV and other DNA damaging agents. In particular, (p)ppGpp seems to stimulate the efficiency of nucleotide excision repair (NER)-dependent repair of DNA lesions. Finally, we discuss whether (p)ppGpp-mediated cell survival during DNA damage is related to the ability of (p)ppGpp accumulation to inhibit chromosome replication.
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Xu J, Wu C, Yang Z, Liu W, Chen H, Batool K, Yao J, Fan X, Wu J, Rao W, Huang T, Xu L, Guan X, Zhang L. For: Pesticide biochemistry and physiology recG is involved with the resistance of Bt to UV. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2020; 167:104599. [PMID: 32527443 DOI: 10.1016/j.pestbp.2020.104599] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Revised: 03/07/2020] [Accepted: 05/06/2020] [Indexed: 06/11/2023]
Abstract
As an ATP-dependent DNA helicase, RecG can repair DNA replication forks in many organisms. However, knowledge of recG in Bacillus thuringiensis (Bt) is limited. In our previous study, recG was found damaged in Bt LLP29-M19, which was more resistant to ultraviolet light (UV) after exposing Bt LLP29 to UV for 19 generations. To further understand the function of recG in the mechanism of Bt UV resistance, recG was knocked out and recovered with homologous recombination technology in Bt LLP29. Comparing the resistance of the different mutants to UVB, Bt ∆recG-LLP29 lacking recG was found more sensitive to UVB, hydroxyurea (HU) and H2O2 than LLP29 and the complementation strain. To compare the expression level of recG in the Bt strains under different UV treatments, Quantitative Real-time PCR (RT-qPCR) of recG was performed in the tested Bt strains, which showed that the expression level of recG in Bt ∆recG-LLP29 was substantially lower than that in the original strain and complementation strain. Interestingly, when exposed to UV for 20 min, RecG expression in both Bt LLP29 and Bt recG-R was the highest. The unwinding activity of recG in Bt LLP29 and the complementation strain were also found higher than that of the recG knockout strain, Bt ∆recG-LLP29. These results demonstrate that recG is involved with the resistance of Bt to UV. These findings not only enhance the understanding of the Bt UV resistance mechanism, but also provide an important theoretical basis for the application of Bt.
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Affiliation(s)
- Jin Xu
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Chenxu Wu
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Zhaohui Yang
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Wencheng Liu
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Hong Chen
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Khadija Batool
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Junmin Yao
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Xiao Fan
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Juan Wu
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Wenhua Rao
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Tianpei Huang
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Lei Xu
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Xiong Guan
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Lingling Zhang
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & School of Life Science, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China.
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18
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Serment-Guerrero J, Dominguez-Monroy V, Davila-Becerril J, Morales-Avila E, Fuentes-Lorenzo JL. Induction of the SOS response of Escherichia coli in repair-defective strains by several genotoxic agents. Mutat Res 2020; 854-855:503196. [PMID: 32660820 DOI: 10.1016/j.mrgentox.2020.503196] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 04/07/2020] [Accepted: 04/21/2020] [Indexed: 11/16/2022]
Abstract
DNA is exposed to the attack of several exogenous agents that modify its chemical structure, so cells must repair those changes in order to survive. Alkylating agents introduce methyl or ethyl groups in most of the cyclic or exocyclic nitrogen atoms of the ring and exocyclic oxygen available in DNA bases producing damage that can induce the SOS response in Escherichia coli and many other bacteria. Likewise, ultraviolet light produces mainly cyclobutane pyrimidine dimers that arrest the progression of the replication fork and triggers such response. The need of some enzymes (such as RecO, ExoI and RecJ) in processing injuries produced by gamma radiation prior the induction of the SOS response has been reported before. In the present work, several repair-defective strains of E. coli were treated with methyl methanesulfonate, ethyl methanesulfonate, mitomycin C or ultraviolet light. Both survival and SOS induction (by means of the Chromotest) were tested. Our results indicate that the participation of these genes depends on the type of injury caused by a genotoxin on DNA.
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Affiliation(s)
- Jorge Serment-Guerrero
- Departamento de Biología, Instituto Nacional de Investigaciones Nucleares, La Marquesa, Estado de México, Mexico.
| | - Viridiana Dominguez-Monroy
- Departamento de Biología, Instituto Nacional de Investigaciones Nucleares, La Marquesa, Estado de México, Mexico
| | - Jenny Davila-Becerril
- Departamento de Biología, Instituto Nacional de Investigaciones Nucleares, La Marquesa, Estado de México, Mexico
| | - Enrique Morales-Avila
- Facultad de Química, Universidad Autónoma del Estado de México, Toluca, Estado de México, Mexico
| | - Jorge Luis Fuentes-Lorenzo
- Laboratorio de Microbiología y Mutagénesis Ambiental, Grupo de Investigación en Microbiología y Genética, Escuela de Biología, Universidad Industrial de Santander, Bucaramanga, Colombia
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19
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Sinha AK, Possoz C, Leach DRF. The Roles of Bacterial DNA Double-Strand Break Repair Proteins in Chromosomal DNA Replication. FEMS Microbiol Rev 2020; 44:351-368. [PMID: 32286623 PMCID: PMC7326373 DOI: 10.1093/femsre/fuaa009] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Accepted: 04/09/2020] [Indexed: 02/06/2023] Open
Abstract
It is well established that DNA double-strand break (DSB) repair is required to underpin chromosomal DNA replication. Because DNA replication forks are prone to breakage, faithful DSB repair and correct replication fork restart are critically important. Cells, where the proteins required for DSB repair are absent or altered, display characteristic disturbances to genome replication. In this review, we analyze how bacterial DNA replication is perturbed in DSB repair mutant strains and explore the consequences of these perturbations for bacterial chromosome segregation and cell viability. Importantly, we look at how DNA replication and DSB repair processes are implicated in the striking recent observations of DNA amplification and DNA loss in the chromosome terminus of various mutant Escherichia coli strains. We also address the mutant conditions required for the remarkable ability to copy the entire E. coli genome, and to maintain cell viability, even in the absence of replication initiation from oriC, the unique origin of DNA replication in wild type cells. Furthermore, we discuss the models that have been proposed to explain these phenomena and assess how these models fit with the observed data, provide new insights and enhance our understanding of chromosomal replication and termination in bacteria.
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Affiliation(s)
- Anurag Kumar Sinha
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, Copenhagen, 2200, Denmark
| | - Christophe Possoz
- Evolution and maintenance of circular chromosomes, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, 1 avenue de la Terrasse Building 26, 91198 Gif-sur-Yvette, France
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh, EH9 3FF, United Kingdom
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20
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Romero ZJ, Armstrong TJ, Henrikus SS, Chen SH, Glass DJ, Ferrazzoli AE, Wood EA, Chitteni-Pattu S, van Oijen AM, Lovett ST, Robinson A, Cox MM. Frequent template switching in postreplication gaps: suppression of deleterious consequences by the Escherichia coli Uup and RadD proteins. Nucleic Acids Res 2020; 48:212-230. [PMID: 31665437 PMCID: PMC7145654 DOI: 10.1093/nar/gkz960] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2019] [Revised: 10/03/2019] [Accepted: 10/16/2019] [Indexed: 12/21/2022] Open
Abstract
When replication forks encounter template DNA lesions, the lesion is simply skipped in some cases. The resulting lesion-containing gap must be converted to duplex DNA to permit repair. Some gap filling occurs via template switching, a process that generates recombination-like branched DNA intermediates. The Escherichia coli Uup and RadD proteins function in different pathways to process the branched intermediates. Uup is a UvrA-like ABC family ATPase. RadD is a RecQ-like SF2 family ATPase. Loss of both functions uncovers frequent and RecA-independent deletion events in a plasmid-based assay. Elevated levels of crossing over and repeat expansions accompany these deletion events, indicating that many, if not most, of these events are associated with template switching in postreplication gaps as opposed to simple replication slippage. The deletion data underpin simulations indicating that multiple postreplication gaps may be generated per replication cycle. Both Uup and RadD bind to branched DNAs in vitro. RadD protein suppresses crossovers and Uup prevents nucleoid mis-segregation. Loss of Uup and RadD function increases sensitivity to ciprofloxacin. We present Uup and RadD as genomic guardians. These proteins govern two pathways for resolution of branched DNA intermediates such that potentially deleterious genome rearrangements arising from frequent template switching are averted.
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Affiliation(s)
- Zachary J Romero
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Thomas J Armstrong
- Molecular Horizons Institute and School of Chemistry, University of Wollongong, Wollongong, Australia.,Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Sarah S Henrikus
- Molecular Horizons Institute and School of Chemistry, University of Wollongong, Wollongong, Australia.,Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Stefanie H Chen
- Biotechnology Program, North Carolina State University, Raleigh, NC 27695, USA.,Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA
| | - David J Glass
- Department of Biology and Rosenstiel Center, Brandeis University, Waltham, MA 02453, USA
| | - Alexander E Ferrazzoli
- Department of Biology and Rosenstiel Center, Brandeis University, Waltham, MA 02453, USA
| | - Elizabeth A Wood
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | | | - Antoine M van Oijen
- Molecular Horizons Institute and School of Chemistry, University of Wollongong, Wollongong, Australia.,Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Susan T Lovett
- Department of Biology and Rosenstiel Center, Brandeis University, Waltham, MA 02453, USA
| | - Andrew Robinson
- Molecular Horizons Institute and School of Chemistry, University of Wollongong, Wollongong, Australia.,Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Michael M Cox
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
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21
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Buljubašić M, Hlevnjak A, Repar J, Đermić D, Filić V, Weber I, Zahradka K, Zahradka D. RecBCD- RecFOR-independent pathway of homologous recombination in Escherichia coli. DNA Repair (Amst) 2019; 83:102670. [PMID: 31378505 DOI: 10.1016/j.dnarep.2019.102670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Revised: 07/05/2019] [Accepted: 07/05/2019] [Indexed: 10/26/2022]
Abstract
The RecA protein is a key bacterial recombination enzyme that catalyzes pairing and strand exchange between homologous DNA duplexes. In Escherichia coli, RecA protein assembly on DNA is mediated either by the RecBCD or RecFOR protein complexes. Correspondingly, two recombination pathways, RecBCD and RecF (or RecFOR), are distinguished in E. coli. Inactivation of both pathways in recB(CD) recF(OR) mutants results in severe recombination deficiency. Here we describe a novel, RecBCD- RecFOR-independent (RecBFI) recombination pathway that is active in ΔrecBCD sbcB15 sbcC(D) ΔrecF(OR) mutants of E. coli. In transductional crosses, these mutants show only four-fold decrease of recombination frequency relative to the wild-type strain. At the same time they recombine 40- to 90-fold better than their sbcB+ sbcC+ and ΔsbcB sbcC counterparts. The RecBFI pathway strongly depends on recA, recJ and recQ gene functions, and moderately depends on recG and lexA functions. Inactivation of dinI, helD, recX, recN, radA, ruvABC and uvrD genes has a slight effect on RecBFI recombination. After exposure to UV and gamma irradiation, the ΔrecBCD sbcB15 sbcC ΔrecF mutants show moderately increased DNA repair proficiency relative to their sbcB+ sbcC+ and ΔsbcB sbcC counterparts. However, introduction of recA730 allele (encoding RecA protein with enhanced DNA binding properties) completely restores repair proficiency to ΔrecBCD sbcB15 sbcC ΔrecF mutants, but not to their sbcB+ sbcC+ and ΔsbcB sbcC derivatives. Fluorescence microscopy with UV-irradiated recA-gfp fusion mutants suggests that the kinetics of RecA filament formation might be slowed down in the RecBFI pathway. Inactivation of 3'-5' exonucleases ExoVII, ExoIX and ExoX cannot activate the RecBFI pathway in ΔrecBCD ΔsbcB sbcC ΔrecF mutants. Taken together, our results show that the product of the sbcB15 allele is crucial for RecBFI pathway. Besides protecting 3' overhangs, SbcB15 protein might play an additional, more active role in formation of the RecA filament.
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Affiliation(s)
- Maja Buljubašić
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Ana Hlevnjak
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Jelena Repar
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Damir Đermić
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Vedrana Filić
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Igor Weber
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Ksenija Zahradka
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Davor Zahradka
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia.
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Thymineless Death in Escherichia coli Is Unaffected by Chromosomal Replication Complexity. J Bacteriol 2019; 201:JB.00797-18. [PMID: 30745374 DOI: 10.1128/jb.00797-18] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 02/06/2019] [Indexed: 11/20/2022] Open
Abstract
Thymineless death (TLD) is a rapid loss of viability of unclear mechanism in cultures of thyA mutants starved for thymine/thymidine (T starvation). It is accepted that T starvation repeatedly breaks replication forks, while recombinational repair restores them, but when the resulting futile breakage-repair cycle affects the small replication bubbles at oriC, the origin is degraded, killing the cell. Indeed, cells with increased chromosomal replication complexity (CRC), expressed as an elevated origin/terminus (ori/ter) ratio, die more extensively during TLD. Here we tested this logic by elevating the CRC in Escherichia coli thyA mutants before T starvation, anticipating exaggerated TLD. Unexpectedly, TLD remained unaffected by a CRC increase to either the natural limit (ori/ter ratio, ∼6) or the functional limit (ori/ter ratio, ∼16). Moreover, when we forced the CRC over the functional limit (ori/ter ratio, ∼30), TLD lessened. Thus, prior overinitiation does not sensitize cells to TLD. In contradiction with the published results, even blocking new replication initiations by the dnaA(Ts) defect at 42°C fails to prevent TLD. Using the thyA dnaA(Ts) mutant in a new T starvation protocol that excludes new initiations, we show that at 42°C, the same degree of TLD still occurs when chromosomes are demonstrably nonreplicating. Remarkably, 80% of the chromosomal DNA in these nonreplicating T-starved cells is still lost, by an unclear mechanism.IMPORTANCE Thymineless death kills cells of any type and is used in anticancer and antimicrobial treatments. We tested the idea that the more replication forks there are in the chromosome during growth, the more extensive the resulting thymineless death. We varied the number of replication forks in the Escherichia coli chromosome, as measured by the origin-to-terminus ratio, ranging it from the normal 2 to 60, and even completely eliminated replication forks in the nonreplicating chromosomes (ori/ter ratio = 1). Unexpectedly, we found that thymineless death is unaffected by the intensity of replication or by its complete absence; we also found that even nonreplicating chromosomes still disappear during thymine starvation. We conclude that thymineless death can kill E. coli independently of chromosomal replication.
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23
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Rao TVP, Kuzminov A. Sources of thymidine and analogs fueling futile damage-repair cycles and ss-gap accumulation during thymine starvation in Escherichia coli. DNA Repair (Amst) 2019; 75:1-17. [PMID: 30684682 PMCID: PMC6382538 DOI: 10.1016/j.dnarep.2019.01.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2018] [Revised: 12/31/2018] [Accepted: 01/06/2019] [Indexed: 10/27/2022]
Abstract
Thymine deprivation in thyA mutant E. coli causes thymineless death (TLD) and is the mode of action of popular antibacterial and anticancer drugs, yet the mechanisms of TLD are still unclear. TLD comprises three defined phases: resistance, rapid exponential death (RED) and survival, with the nature of the resistance phase and of the transition to the RED phase holding key to TLD pathology. We propose that a limited source of endogenous thymine maintains replication forks through the resistance phase. When this source ends, forks undergo futile break-repair cycle during the RED phase, eventually rendering the chromosome non-functional. Two obvious sources of the endogenous thymine are degradation of broken chromosomal DNA and recruitment of thymine from stable RNA. However, mutants that cannot degrade broken chromosomal DNA or lack ribo-thymine, instead of shortening the resistance phase, deepen the RED phase, meaning that only a small fraction of T-starved cells tap into these sources. Interestingly, the substantial chromosomal DNA accumulation during the resistance phase is negated during the RED phase, suggesting futile cycle of incorporation and excision of wrong nucleotides. We tested incorporation of dU or rU, finding some evidence for both, but DNA-dU incorporation accelerates TLD only when intracellular [dUTP] is increased by the dut mutation. In the dut ung mutant, with increased DNA-dU incorporation and no DNA-dU excision, replication is in fact rescued even without dT, but TLD still occurs, suggesting different mechanisms. Finally, we found that continuous DNA synthesis during thymine starvation makes chromosomal DNA increasingly single-stranded, and even the dut ung defect does not completely block this ss-gap accumulation. We propose that instability of single-strand gaps underlies the pathology of thymine starvation.
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Affiliation(s)
- T V Pritha Rao
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
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24
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Klein HL, Bačinskaja G, Che J, Cheblal A, Elango R, Epshtein A, Fitzgerald DM, Gómez-González B, Khan SR, Kumar S, Leland BA, Marie L, Mei Q, Miné-Hattab J, Piotrowska A, Polleys EJ, Putnam CD, Radchenko EA, Saada AA, Sakofsky CJ, Shim EY, Stracy M, Xia J, Yan Z, Yin Y, Aguilera A, Argueso JL, Freudenreich CH, Gasser SM, Gordenin DA, Haber JE, Ira G, Jinks-Robertson S, King MC, Kolodner RD, Kuzminov A, Lambert SAE, Lee SE, Miller KM, Mirkin SM, Petes TD, Rosenberg SM, Rothstein R, Symington LS, Zawadzki P, Kim N, Lisby M, Malkova A. Guidelines for DNA recombination and repair studies: Cellular assays of DNA repair pathways. MICROBIAL CELL (GRAZ, AUSTRIA) 2019; 6:1-64. [PMID: 30652105 PMCID: PMC6334234 DOI: 10.15698/mic2019.01.664] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/24/2018] [Revised: 08/29/2018] [Accepted: 09/14/2018] [Indexed: 12/29/2022]
Abstract
Understanding the plasticity of genomes has been greatly aided by assays for recombination, repair and mutagenesis. These assays have been developed in microbial systems that provide the advantages of genetic and molecular reporters that can readily be manipulated. Cellular assays comprise genetic, molecular, and cytological reporters. The assays are powerful tools but each comes with its particular advantages and limitations. Here the most commonly used assays are reviewed, discussed, and presented as the guidelines for future studies.
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Affiliation(s)
- Hannah L. Klein
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | - Giedrė Bačinskaja
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Jun Che
- Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA
| | - Anais Cheblal
- Friedrich Miescher Institute for Biomedical Research (FMI), 4058 Basel, Switzerland
| | - Rajula Elango
- Department of Biology, University of Iowa, Iowa City, IA, USA
| | - Anastasiya Epshtein
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | - Devon M. Fitzgerald
- Dan L Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Belén Gómez-González
- Centro Andaluz de BIología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla, Seville, Spain
| | - Sharik R. Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Sandeep Kumar
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | | | - Léa Marie
- Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY, USA
| | - Qian Mei
- Systems, Synthetic and Physical Biology Graduate Program, Rice University, Houston, TX, USA
| | - Judith Miné-Hattab
- Institut Curie, PSL Research University, CNRS, UMR3664, F-75005 Paris, France
- Sorbonne Université, Institut Curie, CNRS, UMR3664, F-75005 Paris, France
| | - Alicja Piotrowska
- NanoBioMedical Centre, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland
| | | | - Christopher D. Putnam
- Ludwig Institute for Cancer Research, University of California School of Medicine, San Diego, La Jolla, CA, USA
- Department of Medicine, University of California School of Medicine, San Diego, La Jolla, CA, USA
| | | | - Anissia Ait Saada
- Institut Curie, PSL Research University, CNRS, UMR3348 F-91405, Orsay, France
- University Paris Sud, Paris-Saclay University, CNRS, UMR3348, F-91405, Orsay, France
| | - Cynthia J. Sakofsky
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Durham, NC, USA
| | - Eun Yong Shim
- Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA
| | - Mathew Stracy
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Jun Xia
- Dan L Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Zhenxin Yan
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Yi Yin
- Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, NC USA
| | - Andrés Aguilera
- Centro Andaluz de BIología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla, Seville, Spain
| | - Juan Lucas Argueso
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, USA
| | - Catherine H. Freudenreich
- Department of Biology, Tufts University, Medford, MA USA
- Program in Genetics, Tufts University, Boston, MA, USA
| | - Susan M. Gasser
- Friedrich Miescher Institute for Biomedical Research (FMI), 4058 Basel, Switzerland
| | - Dmitry A. Gordenin
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Durham, NC, USA
| | - James E. Haber
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, USA
| | - Grzegorz Ira
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Sue Jinks-Robertson
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC USA
| | | | - Richard D. Kolodner
- Ludwig Institute for Cancer Research, University of California School of Medicine, San Diego, La Jolla, CA, USA
- Department of Cellular and Molecular Medicine, University of California School of Medicine, San Diego, La Jolla, CA, USA
- Moores-UCSD Cancer Center, University of California School of Medicine, San Diego, La Jolla, CA, USA
- Institute of Genomic Medicine, University of California School of Medicine, San Diego, La Jolla, CA, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Sarah AE Lambert
- Institut Curie, PSL Research University, CNRS, UMR3348 F-91405, Orsay, France
- University Paris Sud, Paris-Saclay University, CNRS, UMR3348, F-91405, Orsay, France
| | - Sang Eun Lee
- Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA
| | - Kyle M. Miller
- Dan L Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, USA
| | | | - Thomas D. Petes
- Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, NC USA
| | - Susan M. Rosenberg
- Dan L Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
- Systems, Synthetic and Physical Biology Graduate Program, Rice University, Houston, TX, USA
| | - Rodney Rothstein
- Department of Genetics & Development, Columbia University Irving Medical Center, New York, NY, USA
| | - Lorraine S. Symington
- Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY, USA
| | - Pawel Zawadzki
- NanoBioMedical Centre, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland
| | - Nayun Kim
- Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center at Houston, Houston, TX, USA
| | - Michael Lisby
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA, USA
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25
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Wong HL, White RA, Visscher PT, Charlesworth JC, Vázquez-Campos X, Burns BP. Disentangling the drivers of functional complexity at the metagenomic level in Shark Bay microbial mat microbiomes. ISME JOURNAL 2018; 12:2619-2639. [PMID: 29980796 DOI: 10.1038/s41396-018-0208-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Revised: 04/27/2018] [Accepted: 06/01/2018] [Indexed: 11/09/2022]
Abstract
The functional metagenomic potential of Shark Bay microbial mats was examined for the first time at a millimeter scale, employing shotgun sequencing of communities via the Illumina NextSeq 500 platform in conjunction with defined chemical analyses. A detailed functional metagenomic profile has elucidated key pathways and facilitated inference of critical microbial interactions. In addition, 87 medium-to-high-quality metagenome-assembled genomes (MAG) were assembled, including potentially novel bins under the deep-branching archaeal Asgard group (Thorarchaetoa and Lokiarchaeota). A range of pathways involved in carbon, nitrogen, sulfur, and phosphorus cycles were identified in mat metagenomes, with the Wood-Ljungdahl pathway over-represented and inferred as a major carbon fixation mode. The top five sets of genes were affiliated to sulfate assimilation (cysNC cysNCD, sat), methanogenesis (hdrABC), Wood-Ljungdahl pathways (cooS, coxSML), phosphate transport (pstB), and copper efflux (copA). Polyhydroxyalkanoate (PHA) synthase genes were over-represented at the surface, with PHA serving as a potential storage of fixed carbon. Sulfur metabolism genes were highly represented, in particular complete sets of genes responsible for both assimilatory and dissimilatory sulfate reduction. Pathways of environmental adaptation (UV, hypersalinity, oxidative stress, and heavy metal resistance) were also delineated, as well as putative viral defensive mechanisms (core genes of the CRISPR, BREX, and DISARM systems). This study provides new metagenome-based models of how biogeochemical cycles and adaptive responses may be partitioned in the microbial mats of Shark Bay.
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Affiliation(s)
- Hon Lun Wong
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia.,Australian Centre for Astrobiology, University of New South Wales Sydney, Sydney, NSW, Australia
| | - Richard Allen White
- Institute of Biological Chemistry, Washington State University, Pullman, USA
| | - Pieter T Visscher
- Australian Centre for Astrobiology, University of New South Wales Sydney, Sydney, NSW, Australia.,Department of Marine Sciences, University of Connecticut, Storrs, CT, USA
| | - James C Charlesworth
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia.,Australian Centre for Astrobiology, University of New South Wales Sydney, Sydney, NSW, Australia
| | - Xabier Vázquez-Campos
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia
| | - Brendan P Burns
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia. .,Australian Centre for Astrobiology, University of New South Wales Sydney, Sydney, NSW, Australia.
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26
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Abstract
In all organisms, replication impairments are an important source of genome rearrangements, mainly because of the formation of double-stranded DNA (dsDNA) ends at inactivated replication forks. Three reactions for the formation of dsDNA ends at replication forks were originally described for Escherichia coli and became seminal models for all organisms: the encounter of replication forks with preexisting single-stranded DNA (ssDNA) interruptions, replication fork reversal, and head-to-tail collisions of successive replication rounds. Here, we first review the experimental evidence that now allows us to know when, where, and how these three different reactions occur in E. coli. Next, we recall our recent studies showing that in wild-type E. coli, spontaneous replication fork breakage occurs in 18% of cells at each generation. We propose that it results from the replication of preexisting nicks or gaps, since it does not involve replication fork reversal or head-to-tail fork collisions. In the recB mutant, deficient for double-strand break (DSB) repair, fork breakage triggers DSBs in the chromosome terminus during cell division, a reaction that is heritable for several generations. Finally, we recapitulate several observations suggesting that restart from intact inactivated replication forks and restart from recombination intermediates require different sets of enzymatic activities. The finding that 18% of cells suffer replication fork breakage suggests that DNA remains intact at most inactivated forks. Similarly, only 18% of cells need the helicase loader for replication restart, which leads us to speculate that the replicative helicase remains on DNA at intact inactivated replication forks and is reactivated by the replication restart proteins.
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27
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Khan SR, Kuzminov A. Degradation of RNA during lysis of Escherichia coli cells in agarose plugs breaks the chromosome. PLoS One 2017; 12:e0190177. [PMID: 29267353 PMCID: PMC5739488 DOI: 10.1371/journal.pone.0190177] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Accepted: 12/08/2017] [Indexed: 11/18/2022] Open
Abstract
The nucleoid of Escherichia coli comprises DNA, nucleoid associated proteins (NAPs) and RNA, whose role is unclear. We found that lysing bacterial cells embedded in agarose plugs in the presence of RNases caused massive fragmentation of the chromosomal DNA. This RNase-induced chromosomal fragmentation (RiCF) was completely dependent on the presence of RNase around lysing cells, while the maximal chromosomal breakage required fast cell lysis. Cell lysis in plugs without RNAse made the chromosomal DNA resistant to subsequent RNAse treatment. RiCF was not influenced by changes in the DNA supercoiling, but was influenced by growth temperature or age of the culture. RiCF was partially dependent on H-NS, histone-like nucleoid structuring- and global transcription regulator protein. The hupAB deletion of heat-unstable nucleoid protein (HU) caused increase in spontaneous fragmentation that was further increased when combined with deletions in two non-coding RNAs, nc1 and nc5. RiCF was completely dependent upon endonuclease I, a periplasmic deoxyribonuclease that is normally found inhibited by cellular RNA. Unlike RiCF, the spontaneous fragmentation in hupAB nc1 nc5 quadruple mutant was resistant to deletion of endonuclease I. RiCF-like phenomenon was observed without addition of RNase to agarose plugs if EDTA was significantly reduced during cell lysis. Addition of RNase under this condition was synergistic, breaking chromosomes into pieces too small to be retained by the pulsed field gels. RNase-independent fragmentation was qualitatively and quantitatively comparable to RiCF and was partially mediated by endonuclease I.
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Affiliation(s)
- Sharik R. Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- * E-mail:
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
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28
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du Lac M, Scarpelli AH, Younger AKD, Bates DG, Leonard JN. Predicting the Dynamics and Heterogeneity of Genomic DNA Content within Bacterial Populations across Variable Growth Regimes. ACS Synth Biol 2017; 6:1131-1139. [PMID: 27689718 DOI: 10.1021/acssynbio.5b00217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
For many applications in microbial synthetic biology, optimizing a desired function requires careful tuning of the degree to which various genes are expressed. One challenge for predicting such effects or interpreting typical characterization experiments is that in bacteria such as E. coli, genome copy number varies widely across different phases and rates of growth, which also impacts how and when genes are expressed from different loci. While such phenomena are relatively well-understood at a mechanistic level, our quantitative understanding of such processes is essentially limited to ideal exponential growth. In contrast, common experimental phenomena such as growth on heterogeneous media, metabolic adaptation, and oxygen restriction all cause substantial deviations from ideal exponential growth, particularly as cultures approach the higher densities at which industrial biomanufacturing and even routine screening experiments are conducted. To meet the need for predicting and explaining how gene dosage impacts cellular functions outside of exponential growth, we here report a novel modeling strategy that leverages agent-based simulation and high performance computing to robustly predict the dynamics and heterogeneity of genomic DNA content within bacterial populations across variable growth regimes. We show that by feeding routine experimental data, such as optical density time series, into our heterogeneous multiphasic growth simulator, we can predict genomic DNA distributions over a range of nonexponential growth conditions. This modeling strategy provides an important advance in the ability of synthetic biologists to evaluate the role of genomic DNA content and heterogeneity in affecting the performance of existing or engineered microbial functions.
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Affiliation(s)
- Melchior du Lac
- Warwick
Integrative Synthetic Biology Centre, School of Engineering, University of Warwick, Coventry CV4 7AL, United Kingdom
| | | | | | - Declan G. Bates
- Warwick
Integrative Synthetic Biology Centre, School of Engineering, University of Warwick, Coventry CV4 7AL, United Kingdom
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29
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Moore JM, Correa R, Rosenberg SM, Hastings PJ. Persistent damaged bases in DNA allow mutagenic break repair in Escherichia coli. PLoS Genet 2017; 13:e1006733. [PMID: 28727736 PMCID: PMC5542668 DOI: 10.1371/journal.pgen.1006733] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 08/03/2017] [Accepted: 04/03/2017] [Indexed: 12/31/2022] Open
Abstract
Bacteria, yeast and human cancer cells possess mechanisms of mutagenesis upregulated by stress responses. Stress-inducible mutagenesis potentially accelerates adaptation, and may provide important models for mutagenesis that drives cancers, host pathogen interactions, antibiotic resistance and possibly much of evolution generally. In Escherichia coli repair of double-strand breaks (DSBs) becomes mutagenic, using low-fidelity DNA polymerases under the control of the SOS DNA-damage response and RpoS general stress response, which upregulate and allow the action of error-prone DNA polymerases IV (DinB), II and V to make mutations during repair. Pol IV is implied to compete with and replace high-fidelity DNA polymerases at the DSB-repair replisome, causing mutagenesis. We report that up-regulated Pol IV is not sufficient for mutagenic break repair (MBR); damaged bases in the DNA are also required, and that in starvation-stressed cells, these are caused by reactive-oxygen species (ROS). First, MBR is reduced by either ROS-scavenging agents or constitutive activation of oxidative-damage responses, both of which reduce cellular ROS levels. The ROS promote MBR other than by causing DSBs, saturating mismatch repair, oxidizing proteins, or inducing the SOS response or the general stress response. We find that ROS drive MBR through oxidized guanines (8-oxo-dG) in DNA, in that overproduction of a glycosylase that removes 8-oxo-dG from DNA prevents MBR. Further, other damaged DNA bases can substitute for 8-oxo-dG because ROS-scavenged cells resume MBR if either DNA pyrimidine dimers or alkylated bases are induced. We hypothesize that damaged bases in DNA pause the replisome and allow the critical switch from high fidelity to error-prone DNA polymerases in the DSB-repair replisome, thus allowing MBR. The data imply that in addition to the indirect stress-response controlled switch to MBR, a direct cis-acting switch to MBR occurs independently of DNA breakage, caused by ROS oxidation of DNA potentially regulated by ROS regulators.
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Affiliation(s)
- Jessica M. Moore
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Raul Correa
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Susan M. Rosenberg
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America
| | - P. J. Hastings
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, Texas, United States of America
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30
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Abstract
In bacteria, replication forks assembled at a replication origin travel to the terminus, often a few megabases away. They may encounter obstacles that trigger replisome disassembly, rendering replication restart from abandoned forks crucial for cell viability. During the past 25 years, the genes that encode replication restart proteins have been identified and genetically characterized. In parallel, the enzymes were purified and analyzed in vitro, where they can catalyze replication initiation in a sequence-independent manner from fork-like DNA structures. This work also revealed a close link between replication and homologous recombination, as replication restart from recombination intermediates is an essential step of DNA double-strand break repair in bacteria and, conversely, arrested replication forks can be acted upon by recombination proteins and converted into various recombination substrates. In this review, we summarize this intense period of research that led to the characterization of the ubiquitous replication restart protein PriA and its partners, to the definition of several replication restart pathways in vivo, and to the description of tight links between replication and homologous recombination, responsible for the importance of replication restart in the maintenance of genome stability.
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31
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Khan SR, Kuzminov A. Pulsed-field gel electrophoresis does not break E. coli chromosome undergoing excision repair after UV irradiation. Anal Biochem 2017; 526:66-68. [PMID: 28351616 DOI: 10.1016/j.ab.2017.03.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 03/23/2017] [Accepted: 03/24/2017] [Indexed: 10/19/2022]
Abstract
We showed before that long linear DNA molecules containing single-strand interruptions and undergoing pulsed-field gel electrophoresis (PFGE) tend to break into subfragments (electrophoretic nick instability). Here we show that circular chromosomal DNA with single-strand interruptions remains in the wells during PFGE. This means that the presence of nicks in immobile circular DNA is not enough to break this DNA during PFGE. In other words, under the conditions of our study, the artifactual conversion of nicks into double-strand breaks that we detect in linear DNA does not contribute to the overall level of chromosomal fragmentation, as measured by PFGE.
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Affiliation(s)
- Sharik R Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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32
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Azeroglu B, Leach DRF. RecG controls DNA amplification at double-strand breaks and arrested replication forks. FEBS Lett 2017; 591:1101-1113. [PMID: 28155219 PMCID: PMC5412681 DOI: 10.1002/1873-3468.12583] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 01/13/2017] [Accepted: 01/28/2017] [Indexed: 12/16/2022]
Abstract
DNA amplification is a powerful mutational mechanism that is a hallmark of cancer and drug resistance. It is therefore important to understand the fundamental pathways that cells employ to avoid over‐replicating sections of their genomes. Recent studies demonstrate that, in the absence of RecG, DNA amplification is observed at sites of DNA double‐strand break repair (DSBR) and of DNA replication arrest that are processed to generate double‐strand ends. RecG also plays a role in stabilising joint molecules formed during DSBR. We propose that RecG prevents a previously unrecognised mechanism of DNA amplification that we call reverse‐restart, which generates DNA double‐strand ends from incorrect loading of the replicative helicase at D‐loops formed by recombination, and at arrested replication forks.
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Affiliation(s)
- Benura Azeroglu
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, UK
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, UK
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33
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Mahaseth T, Kuzminov A. Prompt repair of hydrogen peroxide-induced DNA lesions prevents catastrophic chromosomal fragmentation. DNA Repair (Amst) 2016; 41:42-53. [PMID: 27078578 PMCID: PMC4851570 DOI: 10.1016/j.dnarep.2016.03.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 03/25/2016] [Indexed: 12/13/2022]
Abstract
Iron-dependent oxidative DNA damage in vivo by hydrogen peroxide (H2O2, HP) induces copious single-strand(ss)-breaks and base modifications. HP also causes infrequent double-strand DNA breaks, whose relationship to the cell killing is unclear. Since hydrogen peroxide only fragments chromosomes in growing cells, these double-strand breaks were thought to represent replication forks collapsed at direct or excision ss-breaks and to be fully reparable. We have recently reported that hydrogen peroxide kills Escherichia coli by inducing catastrophic chromosome fragmentation, while cyanide (CN) potentiates both the killing and fragmentation. Remarkably, the extreme density of CN+HP-induced chromosomal double-strand breaks makes involvement of replication forks unlikely. Here we show that this massive fragmentation is further amplified by inactivation of ss-break repair or base-excision repair, suggesting that unrepaired primary DNA lesions are directly converted into double-strand breaks. Indeed, blocking DNA replication lowers CN+HP-induced fragmentation only ∼2-fold, without affecting the survival. Once cyanide is removed, recombinational repair in E. coli can mend several double-strand breaks, but cannot mend ∼100 breaks spread over the entire chromosome. Therefore, double-strand breaks induced by oxidative damage happen at the sites of unrepaired primary one-strand DNA lesions, are independent of replication and are highly lethal, supporting the model of clustered ss-breaks at the sites of stable DNA-iron complexes.
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Affiliation(s)
- Tulip Mahaseth
- Department of Microbiology, University of Illinois at Urbana-Champaign, USA
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, USA.
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34
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Prada Medina CA, Aristizabal Tessmer ET, Quintero Ruiz N, Serment-Guerrero J, Fuentes JL. Survival and SOS response induction in ultraviolet B irradiated Escherichia coli cells with defective repair mechanisms. Int J Radiat Biol 2016; 92:321-8. [DOI: 10.3109/09553002.2016.1152412] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Cesar Augusto Prada Medina
- Laboratorio de Microbiología y Mutagénesis Ambiental, Grupo de Investigaciòn en Microbiología y Genética, Escuela de Biología, Universidad Industrial de Santander, Bucaramanga, Colombia
| | - Elke Tatjana Aristizabal Tessmer
- Laboratorio de Microbiología y Mutagénesis Ambiental, Grupo de Investigaciòn en Microbiología y Genética, Escuela de Biología, Universidad Industrial de Santander, Bucaramanga, Colombia
| | - Nathalia Quintero Ruiz
- Laboratorio de Microbiología y Mutagénesis Ambiental, Grupo de Investigaciòn en Microbiología y Genética, Escuela de Biología, Universidad Industrial de Santander, Bucaramanga, Colombia
| | - Jorge Serment-Guerrero
- Departamento de Biología, Instituto Nacional de Investigaciones Nucleares, Distrito Federal, México
| | - Jorge Luis Fuentes
- Laboratorio de Microbiología y Mutagénesis Ambiental, Grupo de Investigaciòn en Microbiología y Genética, Escuela de Biología, Universidad Industrial de Santander, Bucaramanga, Colombia
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35
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Khan SR, Mahaseth T, Kouzminova EA, Cronan GE, Kuzminov A. Static and Dynamic Factors Limit Chromosomal Replication Complexity in Escherichia coli, Avoiding Dangers of Runaway Overreplication. Genetics 2016; 202:945-60. [PMID: 26801182 PMCID: PMC4788131 DOI: 10.1534/genetics.115.184697] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 01/17/2016] [Indexed: 12/21/2022] Open
Abstract
We define chromosomal replication complexity (CRC) as the ratio of the copy number of the most replicated regions to that of unreplicated regions on the same chromosome. Although a typical CRC of eukaryotic or bacterial chromosomes is 2, rapidly growing Escherichia coli cells induce an extra round of replication in their chromosomes (CRC = 4). There are also E. coli mutants with stable CRC∼6. We have investigated the limits and consequences of elevated CRC in E. coli and found three limits: the "natural" CRC limit of ∼8 (cells divide more slowly); the "functional" CRC limit of ∼22 (cells divide extremely slowly); and the "tolerance" CRC limit of ∼64 (cells stop dividing). While the natural limit is likely maintained by the eclipse system spacing replication initiations, the functional limit might reflect the capacity of the chromosome segregation system, rather than dedicated mechanisms, and the tolerance limit may result from titration of limiting replication factors. Whereas recombinational repair is beneficial for cells at the natural and functional CRC limits, we show that it becomes detrimental at the tolerance CRC limit, suggesting recombinational misrepair during the runaway overreplication and giving a rationale for avoidance of the latter.
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Affiliation(s)
- Sharik R Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Tulip Mahaseth
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Elena A Kouzminova
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Glen E Cronan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
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36
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Azeroglu B, Mawer JSP, Cockram CA, White MA, Hasan AMM, Filatenkova M, Leach DRF. RecG Directs DNA Synthesis during Double-Strand Break Repair. PLoS Genet 2016; 12:e1005799. [PMID: 26872352 PMCID: PMC4752480 DOI: 10.1371/journal.pgen.1005799] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 12/19/2015] [Indexed: 11/19/2022] Open
Abstract
Homologous recombination provides a mechanism of DNA double-strand break repair (DSBR) that requires an intact, homologous template for DNA synthesis. When DNA synthesis associated with DSBR is convergent, the broken DNA strands are replaced and repair is accurate. However, if divergent DNA synthesis is established, over-replication of flanking DNA may occur with deleterious consequences. The RecG protein of Escherichia coli is a helicase and translocase that can re-model 3-way and 4-way DNA structures such as replication forks and Holliday junctions. However, the primary role of RecG in live cells has remained elusive. Here we show that, in the absence of RecG, attempted DSBR is accompanied by divergent DNA replication at the site of an induced chromosomal DNA double-strand break. Furthermore, DNA double-stand ends are generated in a recG mutant at sites known to block replication forks. These double-strand ends, also trigger DSBR and the divergent DNA replication characteristic of this mutant, which can explain over-replication of the terminus region of the chromosome. The loss of DNA associated with unwinding joint molecules previously observed in the absence of RuvAB and RecG, is suppressed by a helicase deficient PriA mutation (priA300), arguing that the action of RecG ensures that PriA is bound correctly on D-loops to direct DNA replication rather than to unwind joint molecules. This has led us to put forward a revised model of homologous recombination in which the re-modelling of branched intermediates by RecG plays a fundamental role in directing DNA synthesis and thus maintaining genomic stability.
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Affiliation(s)
- Benura Azeroglu
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Julia S. P. Mawer
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Charlotte A. Cockram
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Martin A. White
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - A. M. Mahedi Hasan
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Milana Filatenkova
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - David R. F. Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
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37
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Moore JM, Magnan D, Mojica AK, Núñez MAB, Bates D, Rosenberg SM, Hastings PJ. Roles of Nucleoid-Associated Proteins in Stress-Induced Mutagenic Break Repair in Starving Escherichia coli. Genetics 2015; 201:1349-62. [PMID: 26500258 PMCID: PMC4676537 DOI: 10.1534/genetics.115.178970] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Accepted: 10/18/2015] [Indexed: 01/02/2023] Open
Abstract
The mutagenicity of DNA double-strand break repair in Escherichia coli is controlled by DNA-damage (SOS) and general (RpoS) stress responses, which let error-prone DNA polymerases participate, potentially accelerating evolution during stress. Either base substitutions and indels or genome rearrangements result. Here we discovered that most small basic proteins that compact the genome, nucleoid-associated proteins (NAPs), promote or inhibit mutagenic break repair (MBR) via different routes. Of 15 NAPs, H-NS, Fis, CspE, and CbpA were required for MBR; Dps inhibited MBR; StpA and Hha did neither; and five others were characterized previously. Three essential genes were not tested. Using multiple tests, we found the following: First, Dps, which reduces reactive oxygen species (ROS), inhibited MBR, implicating ROS in MBR. Second, CbpA promoted F' plasmid maintenance, allowing MBR to be measured in an F'-based assay. Third, Fis was required for activation of the SOS DNA-damage response and could be substituted in MBR by SOS-induced levels of DinB error-prone DNA polymerase. Thus, Fis promoted MBR by allowing SOS activation. Fourth, H-NS represses ROS detoxifier sodB and was substituted in MBR by deletion of sodB, which was not otherwise mutagenic. We conclude that normal ROS levels promote MBR and that H-NS promotes MBR by maintaining ROS. CspE positively regulates RpoS, which is required for MBR. Four of five previously characterized NAPs promoted stress responses that enhance MBR. Hence, most NAPs affect MBR, the majority via regulatory functions. The data show that a total of six NAPs promote MBR by regulating stress responses, indicating the importance of nucleoid structure and function to the regulation of MBR and of coupling mutagenesis to stress, creating genetic diversity responsively.
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Affiliation(s)
- Jessica M Moore
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, 77030 Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030
| | - David Magnan
- Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Ana K Mojica
- Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030 Undergraduate Program on Genomic Sciences, National Autonomous University of Mexico, Cuernavaca, 62210, Morelos, Mexico
| | - María Angélica Bravo Núñez
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, 77030 Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - David Bates
- Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, 77030
| | - Susan M Rosenberg
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, 77030 Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, 77030
| | - P J Hastings
- Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, 77030 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
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Mahaseth T, Kuzminov A. Cyanide enhances hydrogen peroxide toxicity by recruiting endogenous iron to trigger catastrophic chromosomal fragmentation. Mol Microbiol 2015; 96:349-67. [PMID: 25598241 DOI: 10.1111/mmi.12938] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/15/2015] [Indexed: 11/28/2022]
Abstract
Hydrogen peroxide (HP) or cyanide (CN) are bacteriostatic at low-millimolar concentrations for growing Escherichia coli, whereas CN + HP mixture is strongly bactericidal. We show that this synergistic toxicity is associated with catastrophic chromosomal fragmentation. Since CN alone does not kill at any concentration, while HP alone kills at 20 mM, CN must potentiate HP poisoning. The CN + HP killing is blocked by iron chelators, suggesting Fenton's reaction. Indeed, we show that CN enhances plasmid DNA relaxation due to Fenton's reaction in vitro. However, mutants with elevated iron or HP pools are not acutely sensitive to HP-alone treatment, suggesting that, in addition, in vivo CN recruits iron from intracellular depots. We found that part of the CN-recruited iron pool is managed by ferritin and Dps: ferritin releases iron on cue from CN, while Dps sequesters it, quelling Fenton's reaction. We propose that disrupting intracellular iron trafficking is a common strategy employed by the immune system to kill microbes.
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Affiliation(s)
- Tulip Mahaseth
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801-3709, USA
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Chen SH, Byrne RT, Wood EA, Cox MM. Escherichia coli radD (yejH) gene: a novel function involved in radiation resistance and double-strand break repair. Mol Microbiol 2015; 95:754-68. [PMID: 25425430 DOI: 10.1111/mmi.12885] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/21/2014] [Indexed: 11/28/2022]
Abstract
A transposon insertion screen implicated the yejH gene in the repair of ionizing radiation-induced damage. The yejH gene, which exhibits significant homology to the human transcription-coupled DNA repair gene XPB, is involved in the repair of double-strand DNA breaks. Deletion of yejH significantly sensitized cells to agents that cause double-strand breaks (ionizing radiation, UV radiation, ciprofloxacin). In addition, deletion of both yejH and radA hypersensitized the cells to ionizing radiation, UV and ciprofloxacin damage, indicating that these two genes have complementary repair functions. The ΔyejH ΔradA double deletion also showed a substantial decline in viability following an induced double-strand DNA break, of a magnitude comparable with the defect measured when the recA, recB, recG or priA genes are deleted. The ATPase activity and C-terminal zinc finger motif of yejH play an important role in its repair function, as targeted mutant alleles of yejH did not rescue sensitivity. We propose that yejH be renamed radD, reflecting its role in the DNA repair of radiation damage.
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Affiliation(s)
- Stefanie H Chen
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
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40
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End of the beginning: elongation and termination features of alternative modes of chromosomal replication initiation in bacteria. PLoS Genet 2015; 11:e1004909. [PMID: 25569209 PMCID: PMC4287441 DOI: 10.1371/journal.pgen.1004909] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In bacterial cells, bidirectional replication of the circular chromosome is initiated from a single origin (oriC) and terminates in an antipodal terminus region such that movement of the pair of replication forks is largely codirectional with transcription. The terminus region is flanked by discrete Ter sequences that act as polar, or direction-dependent, arrest sites for fork progression. Alternative oriC-independent modes of replication initiation are possible, one of which is constitutive stable DNA replication (cSDR) from transcription-associated RNA–DNA hybrids or R-loops. Here, I discuss the distinctive attributes of fork progression and termination associated with different modes of bacterial replication initiation. Two hypothetical models are proposed: that head-on collisions between pairs of replication forks, which are a feature of replication termination in all kingdoms of life, provoke bilateral fork reversal reactions; and that cSDR is characterized by existence of distinct subpopulations in bacterial cultures and a widespread distribution of origins in the genome, each with a small firing potential. Since R-loops are known to exist in eukaryotic cells and to inflict genome damage in G1 phase, it is possible that cSDR-like events promote aberrant replication initiation even in eukaryotes.
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41
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Rotman E, Khan S, Kouzminova E, Kuzminov A. Replication fork inhibition in seqA mutants of Escherichia coli triggers replication fork breakage. Mol Microbiol 2014; 93:50-64. [PMID: 24806348 PMCID: PMC4078979 DOI: 10.1111/mmi.12638] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/02/2014] [Indexed: 01/21/2023]
Abstract
SeqA protein negatively regulates replication initiation in Escherichia coli and is also proposed to organize maturation and segregation of the newly replicated DNA. The seqA mutants suffer from chromosomal fragmentation; since this fragmentation is attributed to defective segregation or nucleoid compaction, two-ended breaks are expected. Instead, we show that, in SeqA's absence, chromosomes mostly suffer one-ended DNA breaks, indicating disintegration of replication forks. We further show that replication forks are unexpectedly slow in seqA mutants. Quantitative kinetics of origin and terminus replication from aligned chromosomes not only confirm origin overinitiation in seqA mutants, but also reveal terminus under-replication, indicating inhibition of replication forks. Pre-/post-labelling studies of the chromosomal fragmentation in seqA mutants suggest events involving single forks, rather than pairs of forks from consecutive rounds rear-ending into each other. We suggest that, in the absence of SeqA, the sister-chromatid cohesion 'safety spacer' is destabilized and completely disappears if the replication fork is inhibited, leading to the segregation fork running into the inhibited replication fork and snapping the latter at single-stranded DNA regions.
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Affiliation(s)
- Ella Rotman
- Department of Microbiology, University of Illinois at Urbana-Champaign
| | - Sharik Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign
| | - Elena Kouzminova
- Department of Microbiology, University of Illinois at Urbana-Champaign
| | - Andrei Kuzminov
- Department of Microbiology, University of Illinois at Urbana-Champaign
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42
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Rass U. Resolving branched DNA intermediates with structure-specific nucleases during replication in eukaryotes. Chromosoma 2013; 122:499-515. [PMID: 24008669 PMCID: PMC3827899 DOI: 10.1007/s00412-013-0431-z] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 08/03/2013] [Accepted: 08/08/2013] [Indexed: 11/29/2022]
Abstract
Genome duplication requires that replication forks track the entire length of every chromosome. When complications occur, homologous recombination-mediated repair supports replication fork movement and recovery. This leads to physical connections between the nascent sister chromatids in the form of Holliday junctions and other branched DNA intermediates. A key role in the removal of these recombination intermediates falls to structure-specific nucleases such as the Holliday junction resolvase RuvC in Escherichia coli. RuvC is also known to cut branched DNA intermediates that originate directly from blocked replication forks, targeting them for origin-independent replication restart. In eukaryotes, multiple structure-specific nucleases, including Mus81-Mms4/MUS81-EME1, Yen1/GEN1, and Slx1-Slx4/SLX1-SLX4 (FANCP) have been implicated in the resolution of branched DNA intermediates. It is becoming increasingly clear that, as a group, they reflect the dual function of RuvC in cleaving recombination intermediates and failing replication forks to assist the DNA replication process.
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Affiliation(s)
- Ulrich Rass
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058, Basel, Switzerland,
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43
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Kreuzer KN. DNA damage responses in prokaryotes: regulating gene expression, modulating growth patterns, and manipulating replication forks. Cold Spring Harb Perspect Biol 2013; 5:a012674. [PMID: 24097899 DOI: 10.1101/cshperspect.a012674] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Recent advances in the area of bacterial DNA damage responses are reviewed here. The SOS pathway is still the major paradigm of bacterial DNA damage response, and recent studies have clarified the mechanisms of SOS induction and key physiological roles of SOS including a very major role in genetic exchange and variation. When considering diverse bacteria, it is clear that SOS is not a uniform pathway with one purpose, but rather a platform that has evolved for differing functions in different bacteria. Relating in part to the SOS response, the field has uncovered multiple apparent cell-cycle checkpoints that assist cell survival after DNA damage and remarkable pathways that induce programmed cell death in bacteria. Bacterial DNA damage responses are also much broader than SOS, and several important examples of LexA-independent regulation will be reviewed. Finally, some recent advances that relate to the replication and repair of damaged DNA will be summarized.
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Affiliation(s)
- Kenneth N Kreuzer
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710
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44
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Amado L, Kuzminov A. Low-molecular-weight DNA replication intermediates in Escherichia coli: mechanism of formation and strand specificity. J Mol Biol 2013; 425:4177-91. [PMID: 23876705 DOI: 10.1016/j.jmb.2013.07.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Revised: 07/12/2013] [Accepted: 07/15/2013] [Indexed: 11/30/2022]
Abstract
Chromosomal DNA replication intermediates, revealed in ligase-deficient conditions in vivo, are of low molecular weight (LMW) independently of the organism, suggesting discontinuous replication of both the leading and the lagging DNA strands. Yet, in vitro experiments with purified enzymes replicating sigma-structured substrates show continuous synthesis of the leading DNA strand in complete absence of ligase, supporting the textbook model of semi-discontinuous DNA replication. The discrepancy between the in vivo and in vitro results is rationalized by proposing that various excision repair events nick continuously synthesized leading strands after synthesis, producing the observed LMW intermediates. Here, we show that, in an Escherichia coli ligase-deficient strain with all known excision repair pathways inactivated, new DNA is still synthesized discontinuously. Furthermore, hybridization to strand-specific targets demonstrates that the LMW replication intermediates come from both the lagging and the leading strands. These results support the model of discontinuous leading strand synthesis in E. coli.
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Affiliation(s)
- Luciana Amado
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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45
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Sinha AK, Pavankumar TL, Kamisetty S, Mittal P, Ray MK. Replication arrest is a major threat to growth at low temperature in Antarctic Pseudomonas syringae Lz4W. Mol Microbiol 2013; 89:792-810. [PMID: 23815755 DOI: 10.1111/mmi.12315] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/27/2013] [Indexed: 11/29/2022]
Abstract
Chromosomal damage was detected previously in the recBCD mutants of the Antarctic bacterium Pseudomonas syringae Lz4W, which accumulated linear chromosomal DNA leading to cell death and growth inhibition at 4°C. RecBCD protein generally repairs DNA double-strand breaks by RecA-dependent homologous recombination pathway. Here we show that ΔrecA mutant of P. syringae is not cold-sensitive. Significantly, inactivation of additional DNA repair genes ruvAB rescued the cold-sensitive phenotype of ΔrecBCD mutant. The ΔrecA and ΔruvAB mutants were UV-sensitive as expected. We propose that, at low temperature DNA replication encounters barriers leading to frequent replication fork (RF) arrest and fork reversal. RuvAB binds to the reversed RFs (RRFs) having Holliday junction-like structures and resolves them upon association with RuvC nuclease to cause linearization of the chromosome, a threat to cell survival. RecBCD prevents this by degrading the RRFs, and facilitates replication re-initiation. This model is consistent with our observation that low temperature-induced DNA lesions do not evoke SOS response in P. syringae. Additional studies show that two other repair genes, radA (encoding a RecA paralogue) and recF are not involved in providing cold resistance to the Antarctic bacterium.
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Affiliation(s)
- Anurag K Sinha
- Centre for Cellular and Molecular Biology Council of Scientific and Industrial Research, Uppal Road, Hyderabad, 500007, India
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46
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Khan SR, Kuzminov A. Trapping and breaking of in vivo nicked DNA during pulsed field gel electrophoresis. Anal Biochem 2013; 443:269-81. [PMID: 23770235 DOI: 10.1016/j.ab.2013.06.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2012] [Revised: 05/30/2013] [Accepted: 06/04/2013] [Indexed: 01/06/2023]
Abstract
Pulsed field gel electrophoresis (PFGE) offers a high-resolution approach to quantify chromosomal fragmentation in bacteria, measured as percentage of chromosomal DNA entering the gel. The degree of separation in pulsed field gel (PFG) depends on the size of DNA as well as various conditions of electrophoresis such as electric field strength, time of electrophoresis, switch time, and buffer composition. Here we describe a new parameter, the structural integrity of the sample DNA itself, that influences its migration through PFGs. We show that subchromosomal fragments containing both spontaneous and DNA damage-induced nicks are prone to breakage during PFGE. Such breakage at single-strand interruptions results in artifactual decrease in molecular weight of linear DNA making accurate determination of the number of double-strand breaks difficult. Although breakage of nicked subchromosomal fragments is field strength independent, some high-molecular-weight subchromosomal fragments are also trapped within wells under the standard PFGE conditions. This trapping can be minimized by lowering the field strength and increasing the time of electrophoresis. We discuss how breakage of nicked DNA may be mechanistically linked to trapping. Our results suggest how to optimize conditions for PFGE when quantifying chromosomal fragmentation induced by DNA damage.
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Affiliation(s)
- Sharik R Khan
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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47
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Repar J, Briški N, Buljubašić M, Zahradka K, Zahradka D. Exonuclease VII is involved in "reckless" DNA degradation in UV-irradiated Escherichia coli. Mutat Res 2012; 750:96-104. [PMID: 23123979 DOI: 10.1016/j.mrgentox.2012.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Revised: 09/17/2012] [Accepted: 10/10/2012] [Indexed: 01/06/2023]
Abstract
The recA mutants of Escherichia coli exhibit an abnormal DNA degradation that starts at sites of double-strand DNA breaks (DSBs), and is mediated by RecBCD exonuclease (ExoV). This "reckless" DNA degradation occurs spontaneously in exponentially growing recA cells, and is stimulated by DNA-damaging agents. We have previously found that the xonA and sbcD mutations, which inactivate exonuclease I (ExoI) and SbcCD nuclease, respectively, markedly suppress "reckless" DNA degradation in UV-irradiated recA cells. In the present work, we show that inactivation of exonuclease VII (ExoVII) by an xseA mutation contributes to attenuation of DNA degradation in UV-irradiated recA mutants. The xseA mutation itself has only a weak effect, however, it acts synergistically with the xonA or sbcD mutations in suppressing "reckless" DNA degradation. The quadruple xseA xonA sbcD recA mutants show no sign of DNA degradation during post-irradiation incubation, suggesting that ExoVII, together with ExoI and SbcCD, plays a crucial role in regulating RecBCD-catalyzed chromosome degradation. We propose that these nucleases act on DSBs to create blunt DNA ends, the preferred substrates for the RecBCD enzyme. In addition, our results show that in UV-irradiated recF recA(+) cells, the xseA, xonA, and sbcD mutations do not affect RecBCD-mediated DNA repair, suggesting that ExoVII, ExoI and SbcCD nucleases are not essential for the initial targeting of RecBCD to DSBs. It is possible that the DNA-blunting activity provided by ExoVII, ExoI and SbcCD is required for an exchange of RecBCD molecules on dsDNA ends during ongoing "reckless" DNA degradation.
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Affiliation(s)
- Jelena Repar
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička, Zagreb, Croatia
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48
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Kuong KJ, Kuzminov A. Disintegration of nascent replication bubbles during thymine starvation triggers RecA- and RecBCD-dependent replication origin destruction. J Biol Chem 2012; 287:23958-70. [PMID: 22621921 DOI: 10.1074/jbc.m112.359687] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Thymineless death strikes cells unable to synthesize DNA precursor dTTP, with the nature of chromosomal damage still unclear. Thymine starvation stalls replication forks, whereas accumulating evidence indicates the replication origin is also affected. Using a novel DNA labeling technique, here we show that replication slowly continues in thymine-starved cells, but the newly synthesized DNA becomes fragmented and degraded. This degradation apparently releases enough thymine to sustain initiation of new replication bubbles from the chromosomal origin, which destabilizes the origin in a RecA-dependent manner. Marker frequency analysis with gene arrays 1) reveals destruction of the origin-centered chromosomal segment in RecA(+) cells; 2) confirms origin accumulation in the recA mutants; and 3) identifies the sites around the origin where destruction initiates in the recBCD mutants. We propose that thymineless cells convert persistent single-strand gaps behind replication forks into double-strand breaks, using the released thymine for new initiations, whereas subsequent disintegration of small replication bubbles causes replication origin destruction.
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Affiliation(s)
- Kawai J Kuong
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3709, USA
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De Septenville AL, Duigou S, Boubakri H, Michel B. Replication fork reversal after replication-transcription collision. PLoS Genet 2012; 8:e1002622. [PMID: 22496668 PMCID: PMC3320595 DOI: 10.1371/journal.pgen.1002622] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Accepted: 02/10/2012] [Indexed: 11/18/2022] Open
Abstract
Replication fork arrest is a recognized source of genetic instability, and transcription is one of the most prominent causes of replication impediment. We analyze here the requirement for recombination proteins in Escherichia coli when replication–transcription head-on collisions are induced at a specific site by the inversion of a highly expressed ribosomal operon (rrn). RecBC is the only recombination protein required for cell viability under these conditions of increased replication-transcription collisions. In its absence, fork breakage occurs at the site of collision, and the resulting linear DNA is not repaired and is slowly degraded by the RecJ exonuclease. Lethal fork breakage is also observed in cells that lack RecA and RecD, i.e. when both homologous recombination and the potent exonuclease V activity of the RecBCD complex are inactivated, with a slow degradation of the resulting linear DNA by the combined action of the RecBC helicase and the RecJ exonuclease. The sizes of the major linear fragments indicate that DNA degradation is slowed down by the encounter with another rrn operon. The amount of linear DNA decreases nearly two-fold when the Holliday junction resolvase RuvABC is inactivated in recB, as well as in recA recD mutants, indicating that part of the linear DNA is formed by resolution of a Holliday junction. Our results suggest that replication fork reversal occurs after replication–transcription head-on collision, and we propose that it promotes the action of the accessory replicative helicases that dislodge the obstacle. Genomes are duplicated prior to cell division by DNA replication, and in all organisms replication impairment leads to chromosome instability. In bacteria, replication and transcription take place simultaneously, and in eukaryotes house-keeping genes are expressed during the S-phase; consequently, transcription is susceptible to impair replication progression. Here, we increase head-on replication–transcription collisions on the bacterial chromosome by inversion of a ribosomal operon (rrn). We show that only one recombination protein is required for growth when the rrn genes are highly expressed: the RecBCD complex, an exonuclease/recombinase that promotes degradation and RecA-dependent homologous recombination of linear DNA. In the absence of RecBCD, we observe linear DNA that ends in the collision region. This linear DNA is composed of only the origin-proximal region of the inverted rrn operon, indicating that it results from fork breakage. It is partly RuvABC-dependent (i.e. produced by the E. coli Holliday junction resolvase), indicating that blocked forks are reversed. The linear DNA ends up at the inverted rrn locus only if the RecJ exonuclease is inactivated; otherwise it is degraded, with major products ending in other upstream rrn operons, indicating that DNA degradation is slowed down by ribosomal operon sequences.
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Affiliation(s)
- Anne L. De Septenville
- CNRS, Centre de Génétique Moléculaire, UPR3404, Gif-sur-Yvette, France
- Université Paris-Sud, Orsay, France
| | - Stéphane Duigou
- CNRS, Centre de Génétique Moléculaire, UPR3404, Gif-sur-Yvette, France
- Université Paris-Sud, Orsay, France
| | - Hasna Boubakri
- CNRS, Centre de Génétique Moléculaire, UPR3404, Gif-sur-Yvette, France
- Université Paris-Sud, Orsay, France
| | - Bénédicte Michel
- CNRS, Centre de Génétique Moléculaire, UPR3404, Gif-sur-Yvette, France
- Université Paris-Sud, Orsay, France
- * E-mail:
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