1
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Bignaud A, Cockram C, Borde C, Groseille J, Allemand E, Thierry A, Marbouty M, Mozziconacci J, Espéli O, Koszul R. Transcription-induced domains form the elementary constraining building blocks of bacterial chromosomes. Nat Struct Mol Biol 2024; 31:489-497. [PMID: 38177686 PMCID: PMC10948358 DOI: 10.1038/s41594-023-01178-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 11/10/2023] [Indexed: 01/06/2024]
Abstract
Transcription generates local topological and mechanical constraints on the DNA fiber, leading to the generation of supercoiled chromosome domains in bacteria. However, the global impact of transcription on chromosome organization remains elusive, as the scale of genes and operons in bacteria remains well below the resolution of chromosomal contact maps generated using Hi-C (~5-10 kb). Here we combined sub-kb Hi-C contact maps and chromosome engineering to visualize individual transcriptional units. We show that transcriptional units form discrete three-dimensional transcription-induced domains that impose mechanical and topological constraints on their neighboring sequences at larger scales, modifying their localization and dynamics. These results show that transcriptional domains constitute primary building blocks of bacterial chromosome folding and locally impose structural and dynamic constraints.
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Affiliation(s)
- Amaury Bignaud
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, Paris, France
- Collège Doctoral, Sorbonne Université, Paris, France
| | - Charlotte Cockram
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, Paris, France
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, Université PSL, Paris, France
| | - Céline Borde
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, Université PSL, Paris, France
| | - Justine Groseille
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, Paris, France
- Collège Doctoral, Sorbonne Université, Paris, France
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, Université PSL, Paris, France
| | - Eric Allemand
- INSERM-U1163, Unité mécanismes cellulaires et moléculaires des désordres hématologiques et implications thérapeutiques, Institut Imagine, Paris, France
| | - Agnès Thierry
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, Paris, France
| | - Martial Marbouty
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, Paris, France
| | - Julien Mozziconacci
- Laboratoire Structure et Instabilité des Génomes, UMR 7196, Muséum National d'Histoire Naturelle, Paris, France
| | - Olivier Espéli
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, Université PSL, Paris, France.
| | - Romain Koszul
- Institut Pasteur, CNRS UMR 3525, Université Paris Cité, Unité Régulation Spatiale des Génomes, Paris, France.
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2
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Pham P, Wood EA, Cox MM, Goodman MF. RecA and SSB genome-wide distribution in ssDNA gaps and ends in Escherichia coli. Nucleic Acids Res 2023; 51:5527-5546. [PMID: 37070184 PMCID: PMC10287960 DOI: 10.1093/nar/gkad263] [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: 12/06/2022] [Revised: 03/29/2023] [Accepted: 03/30/2023] [Indexed: 04/19/2023] Open
Abstract
Single-stranded DNA (ssDNA) gapped regions are common intermediates in DNA transactions. Using a new non-denaturing bisulfite treatment combined with ChIP-seq, abbreviated 'ssGap-seq', we explore RecA and SSB binding to ssDNA on a genomic scale in E. coli in a wide range of genetic backgrounds. Some results are expected. During log phase growth, RecA and SSB assembly profiles coincide globally, concentrated on the lagging strand and enhanced after UV irradiation. Unexpected results also abound. Near the terminus, RecA binding is favored over SSB, binding patterns change in the absence of RecG, and the absence of XerD results in massive RecA assembly. RecA may substitute for the absence of XerCD to resolve chromosome dimers. A RecA loading pathway may exist that is independent of RecBCD and RecFOR. Two prominent and focused peaks of RecA binding revealed a pair of 222 bp and GC-rich repeats, equidistant from dif and flanking the Ter domain. The repeats, here named RRS for replication risk sequence, trigger a genomically programmed generation of post-replication gaps that may play a special role in relieving topological stress during replication termination and chromosome segregation. As demonstrated here, ssGap-seq provides a new window on previously inaccessible aspects of ssDNA metabolism.
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Affiliation(s)
- Phuong Pham
- Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089-2910, USA
| | - Elizabeth A Wood
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706-1544, USA
| | - Michael M Cox
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706-1544, USA
| | - Myron F Goodman
- Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089-2910, USA
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3
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Saleh MA, Elmaaty AA, El Saeed HS, Saleh MM, Salah M, Ezz Eldin RR. Structure based design and synthesis of 3-(7-nitro-3-oxo-3,4-dihydroquinoxalin-2-yl)propanehydrazide derivatives as novel bacterial DNA-gyrase inhibitors: In-vitro, In-vivo, In-silico and SAR studies. Bioorg Chem 2022; 129:106186. [PMID: 36215786 DOI: 10.1016/j.bioorg.2022.106186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 09/26/2022] [Accepted: 09/28/2022] [Indexed: 11/02/2022]
Abstract
Antimicrobial resistance (AMR) is one of the critical challenges that have been encountered over the past years. On the other hand, bacterial DNA gyrase is regarded as one of the most outstanding biological targets that quinolones can extensively inhibit, improving AMR. Hence, a novel series of 3-(7-nitro-3-oxo-3,4-dihydroquinoxalin-2-yl)propanehydrazide derivatives (3-6j) were designed and synthesized employing the quinoxaline-2-one scaffold and relying on the pharmacophoric features experienced by the quinolone antibiotic; ciprofloxacin. The antibacterial activity of the synthesized compounds was assessed via in-vitro approaches using eight different Gram-positive and Gram-negative bacterial species. Most of the synthesized compounds revealed eligible antibacterial activities. In particular, compounds 6d and 6e displayed promising antibacterial activity among the investigated compounds. For example, compounds 6d and 6e displayed MIC values of 9.40 and 9.00 µM, respectively, regarding S. aureus, and 4.70 and 4.50 µM, respectively, regarding S. pneumonia in comparison to ciprofloxacin (12.07 µM). The cytotoxicity of compounds 6d and 6e were performed on normal human WI-38 cell lines with IC50 values of 288.69 and 227.64 μM, respectively assuring their safety and selectivity. Besides, DNA gyrase inhibition assay of compounds 6d and 6e was carried out in comparison to ciprofloxacin, and interestingly, compounds 6d and 6e disclosed promising IC50 values of 0.242 and 0.177 μM, respectively, whereas ciprofloxacin displayed an IC50 value of 0.768 μM, assuring the proposed mechanism of action for the afforded compounds. Consequently, compounds 6d and 6e were further assessed via in-vivo approaches by evaluating blood counts, liver and kidney functions, and histopathological examination. Both compounds were found to be safer on the liver and kidney than the reference ciprofloxacin. Moreover, in-silico molecular docking studies were established and revealed reasonable binding affinities for all afforded compounds, particularly compound 6d which exhibited a binding score of -7.51 kcal/mol, surpassing the reference ciprofloxacin (-7.29 kcal/mol) with better anticipated stability at the DNA gyrase binding pocket. Moreover, ADME studies were conducted, disclosing an eligible bioavailability score of >0.55 for all afforded compounds, and reasonable GIT absorption without passing the blood brain barrier was attained for most investigated compounds, ensuring their efficacy and safety. Lastly, a structure activity relationship study for the synthesized compounds was established and unveiled that not only the main pharmacophores required for DNA gyrase inhibition are enough for exerting promising antimicrobial activities, but also derivatization with diverse aryl/hetero aryl aldehydes is essential for their enhanced antimicrobial potential.
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Affiliation(s)
- Marwa A Saleh
- Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy (Girls), Al-Azhar University, Cairo, Egypt
| | - Ayman Abo Elmaaty
- Medicinal Chemistry Department, Faculty of Pharmacy, Port Said University, Port Said 42526, Egypt.
| | - Hoda S El Saeed
- Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy (Girls), Al-Azhar University, Cairo, Egypt
| | - Moustafa M Saleh
- Microbiology and Immunology Department, Faculty of Pharmacy, Port Said University, Egypt
| | - Mohammed Salah
- Microbiology and Immunology Department, Faculty of Pharmacy, Port Said University, Egypt
| | - Rogy R Ezz Eldin
- Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Port Said University, Port Said, Egypt.
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4
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Wang BB, Xu JZ, Zhang F, Liu S, Liu J, Zhang WG. Review of DNA repair enzymes in bacteria: With a major focus on AddAB and RecBCD. DNA Repair (Amst) 2022; 118:103389. [PMID: 36030574 DOI: 10.1016/j.dnarep.2022.103389] [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: 03/14/2022] [Revised: 07/18/2022] [Accepted: 08/20/2022] [Indexed: 11/03/2022]
Abstract
DNA recombination repair systems are essential for organisms to maintain genomic stability. In recent years, we have improved our understanding of the mechanisms of RecBCD/AddAB family-mediated DNA double-strand break repair. In E. coli, it is RecBCD that plays a central role, and in Firmicute Bacillus subtilis it is the AddAB complex that functions. However, there are open questions about the mechanism of DNA repair in bacteria. For example, how bacteria containing crossover hotspot instigator (Chi) sites regulate the activity of proteins. In addition, we still do not know the exact process by which the RecB nuclease or AddA nuclease structural domains load RecA onto DNA. We also know little about the mechanism of DNA repair in the industrially important production bacterium Corynebacterium glutamicum (C. glutamicum). Therefore, exploring DNA repair mechanisms in bacteria may not only deepen our understanding of the DNA repair process in this species but also guide us in the targeted treatment of diseases associated with recombination defects, such as cancer. In this paper, we firstly review the classical proteins RecBCD and AddAB involved in DNA recombination repair, secondly focus on the novel helical nuclease AdnAB found in the genus Mycobacterium.
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Affiliation(s)
- Bing-Bing Wang
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, WuXi 214122, People's Republic of China
| | - Jian-Zhong Xu
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, WuXi 214122, People's Republic of China.
| | - Feng Zhang
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, WuXi 214122, People's Republic of China
| | - Shuai Liu
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, WuXi 214122, People's Republic of China
| | - Jie Liu
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, WuXi 214122, People's Republic of China
| | - Wei-Guo Zhang
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, WuXi 214122, People's Republic of China.
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5
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Goswami S, Gowrishankar J. Role for DNA double strand end-resection activity of RecBCD in control of aberrant chromosomal replication initiation in Escherichia coli. Nucleic Acids Res 2022; 50:8643-8657. [PMID: 35929028 PMCID: PMC9410895 DOI: 10.1093/nar/gkac670] [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: 05/28/2022] [Revised: 07/13/2022] [Accepted: 08/03/2022] [Indexed: 11/12/2022] Open
Abstract
Replication of the circular bacterial chromosome is initiated from a locus oriC with the aid of an essential protein DnaA. One approach to identify factors acting to prevent aberrant oriC-independent replication initiation in Escherichia coli has been that to obtain mutants which survive loss of DnaA. Here, we show that a ΔrecD mutation, associated with attenuation of RecBCD’s DNA double strand end-resection activity, provokes abnormal replication and rescues ΔdnaA lethality in two situations: (i) in absence of 5′-3′ single-strand DNA exonuclease RecJ, or (ii) when multiple two-ended DNA double strand breaks (DSBs) are generated either by I-SceI endonucleolytic cleavages or by radiomimetic agents phleomycin or bleomycin. One-ended DSBs in the ΔrecD mutant did not rescue ΔdnaA lethality. With two-ended DSBs in the ΔrecD strain, ΔdnaA viability was retained even after linearization of the chromosome. Data from genome-wide DNA copy number determinations in ΔdnaA-rescued cells lead us to propose a model that nuclease-mediated DNA resection activity of RecBCD is critical for prevention of a σ-mode of rolling-circle over-replication when convergent replication forks merge and fuse, as may be expected to occur during normal replication at the chromosomal terminus region or during repair of two-ended DSBs following ‘ends-in’ replication.
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Affiliation(s)
- Sayantan Goswami
- Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500039, India.,Graduate Studies, Manipal Academy of Higher Education, Manipal 576104, India.,Indian Institute of Science Education and Research Mohali, SAS Nagar 140306, India
| | - Jayaraman Gowrishankar
- Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500039, India.,Indian Institute of Science Education and Research Mohali, SAS Nagar 140306, India
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6
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Jaramillo‐Riveri S, Broughton J, McVey A, Pilizota T, Scott M, El Karoui M. Growth-dependent heterogeneity in the DNA damage response in Escherichia coli. Mol Syst Biol 2022; 18:e10441. [PMID: 35620827 PMCID: PMC9136515 DOI: 10.15252/msb.202110441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 04/13/2022] [Accepted: 04/27/2022] [Indexed: 11/16/2022] Open
Abstract
In natural environments, bacteria are frequently exposed to sub-lethal levels of DNA damage, which leads to the induction of a stress response (the SOS response in Escherichia coli). Natural environments also vary in nutrient availability, resulting in distinct physiological changes in bacteria, which may have direct implications on their capacity to repair their chromosomes. Here, we evaluated the impact of varying the nutrient availability on the expression of the SOS response induced by chronic sub-lethal DNA damage in E. coli. We found heterogeneous expression of the SOS regulon at the single-cell level in all growth conditions. Surprisingly, we observed a larger fraction of high SOS-induced cells in slow growth as compared with fast growth, despite a higher rate of SOS induction in fast growth. The result can be explained by the dynamic balance between the rate of SOS induction and the division rates of cells exposed to DNA damage. Taken together, our data illustrate how cell division and physiology come together to produce growth-dependent heterogeneity in the DNA damage response.
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Affiliation(s)
| | - James Broughton
- Institute of Cell Biology and SynthSysUniversity of EdinburghEdinburghUK
| | - Alexander McVey
- Institute of Cell Biology and SynthSysUniversity of EdinburghEdinburghUK
- Present address:
OGI Bio LtdEdinburghUK
| | - Teuta Pilizota
- Institute of Cell Biology and SynthSysUniversity of EdinburghEdinburghUK
| | - Matthew Scott
- Department of Applied MathematicsUniversity of WaterlooWaterlooONCanada
| | - Meriem El Karoui
- Institute of Cell Biology and SynthSysUniversity of EdinburghEdinburghUK
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7
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Wiktor J, Gynnå AH, Leroy P, Larsson J, Coceano G, Testa I, Elf J. RecA finds homologous DNA by reduced dimensionality search. Nature 2021; 597:426-429. [PMID: 34471288 PMCID: PMC8443446 DOI: 10.1038/s41586-021-03877-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 08/04/2021] [Indexed: 11/21/2022]
Abstract
Homologous recombination is essential for the accurate repair of double-stranded DNA breaks (DSBs)1. Initially, the RecBCD complex2 resects the ends of the DSB into 3' single-stranded DNA on which a RecA filament assembles3. Next, the filament locates the homologous repair template on the sister chromosome4. Here we directly visualize the repair of DSBs in single cells, using high-throughput microfluidics and fluorescence microscopy. We find that, in Escherichia coli, repair of DSBs between segregated sister loci is completed in 15 ± 5 min (mean ± s.d.) with minimal fitness loss. We further show that the search takes less than 9 ± 3 min (mean ± s.d) and is mediated by a thin, highly dynamic RecA filament that stretches throughout the cell. We propose that the architecture of the RecA filament effectively reduces search dimensionality. This model predicts a search time that is consistent with our measurement and is corroborated by the observation that the search time does not depend on the length of the cell or the amount of DNA. Given the abundance of RecA homologues5, we believe this model to be widely conserved across living organisms.
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Affiliation(s)
- Jakub Wiktor
- Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Arvid H Gynnå
- Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Prune Leroy
- Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Jimmy Larsson
- Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Giovanna Coceano
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Ilaria Testa
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Johan Elf
- Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
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8
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Yasmin T, Azeroglu B, Cockram CA, Leach DRF. Distribution of Holliday junctions and repair forks during Escherichia coli DNA double-strand break repair. PLoS Genet 2021; 17:e1009717. [PMID: 34432790 PMCID: PMC8386832 DOI: 10.1371/journal.pgen.1009717] [Citation(s) in RCA: 4] [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: 05/13/2021] [Accepted: 07/14/2021] [Indexed: 11/21/2022] Open
Abstract
Accurate repair of DNA double-strand breaks (DSBs) is crucial for cell survival and genome integrity. In Escherichia coli, DSBs are repaired by homologous recombination (HR), using an undamaged sister chromosome as template. The DNA intermediates of this pathway are expected to be branched molecules that may include 4-way structures termed Holliday junctions (HJs), and 3-way structures such as D-loops and repair forks. Using a tool creating a site-specific, repairable DSB on only one of a pair of replicating sister chromosomes, we have determined how these branched DNA intermediates are distributed across a DNA region that is undergoing DSB repair. In cells, where branch migration and cleavage of HJs are limited by inactivation of the RuvABC complex, HJs and repair forks are principally accumulated within a distance of 12 kb from sites of recombination initiation, known as Chi, on each side of the engineered DSB. These branched DNA structures can even be detected in the region of DNA between the Chi sites flanking the DSB, a DNA segment not expected to be engaged in recombination initiation, and potentially degraded by RecBCD nuclease action. This is observed even in the absence of the branch migration and helicase activities of RuvAB, RadA, RecG, RecQ and PriA. The detection of full-length DNA fragments containing HJs in this central region implies that DSB repair can restore the two intact chromosomes, into which HJs can relocate prior to their resolution. The distribution of recombination intermediates across the 12kb region beyond Chi is altered in xonA, recJ and recQ mutants suggesting that, in the RecBCD pathway of DSB repair, exonuclease I stimulates the formation of repair forks and that RecJQ promotes strand-invasion at a distance from the recombination initiation sites.
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Affiliation(s)
- Tahirah Yasmin
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King’s Buildings, Edinburgh, United Kingdom
| | - Benura Azeroglu
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King’s Buildings, Edinburgh, United Kingdom
| | - Charlotte A. Cockram
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King’s Buildings, Edinburgh, United Kingdom
| | - David R. F. Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King’s Buildings, Edinburgh, United Kingdom
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9
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Buton A, Bobay LM. Evolution of Chi motifs in Proteobacteria. G3-GENES GENOMES GENETICS 2021; 11:6064151. [PMID: 33561247 PMCID: PMC8022716 DOI: 10.1093/g3journal/jkaa054] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 11/01/2020] [Indexed: 11/18/2022]
Abstract
Homologous recombination is a key pathway found in nearly all bacterial taxa. The recombination complex not only allows bacteria to repair DNA double-strand breaks but also promotes adaption through the exchange of DNA between cells. In Proteobacteria, this process is mediated by the RecBCD complex, which relies on the recognition of a DNA motif named Chi to initiate recombination. The Chi motif has been characterized in Escherichia coli and analogous sequences have been found in several other species from diverse families, suggesting that this mode of action is widespread across bacteria. However, the sequences of Chi-like motifs are known for only five bacterial species: E. coli, Haemophilus influenzae, Bacillus subtilis, Lactococcus lactis, and Staphylococcus aureus. In this study, we detected putative Chi motifs in a large dataset of Proteobacteria and identified four additional motifs sharing high sequence similarity and similar properties to the Chi motif of E. coli in 85 species of Proteobacteria. Most Chi motifs were detected in Enterobacteriaceae and this motif appears well conserved in this family. However, we did not detect Chi motifs for the majority of Proteobacteria, suggesting that different motifs are used in these species. Altogether these results substantially expand our knowledge on the evolution of Chi motifs and on the recombination process in bacteria.
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Affiliation(s)
- Angélique Buton
- Department of Biology, University of North Carolina Greensboro, Greensboro, NC 27402, USA
| | - Louis-Marie Bobay
- Department of Biology, University of North Carolina Greensboro, Greensboro, NC 27402, USA
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10
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Gurung D, Blumenthal RM. Distribution of RecBCD and AddAB recombination-associated genes among bacteria in 33 phyla. MICROBIOLOGY-SGM 2020; 166:1047-1064. [PMID: 33085588 DOI: 10.1099/mic.0.000980] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Homologous recombination plays key roles in fundamental processes such as recovery from DNA damage and in bacterial horizontal gene transfer, yet there are still open questions about the distribution of recognized components of recombination machinery among bacteria and archaea. RecBCD helicase-nuclease plays a central role in recombination among Gammaproteobacteria like Escherichia coli; while bacteria in other phyla, like the Firmicute Bacillus subtilis, use the related AddAB complex. The activity of at least some of these complexes is controlled by short DNA sequences called crossover hotspot instigator (Chi) sites. When RecBCD or AddAB complexes encounter an autologous Chi site during unwinding, they introduce a nick such that ssDNA with a free end is available to invade another duplex. If homologous DNA is present, RecA-dependent homologous recombination is promoted; if not (or if no autologous Chi site is present) the RecBCD/AddAB complex eventually degrades the DNA. We examined the distribution of recBCD and addAB genes among bacteria, and sought ways to distinguish them unambiguously. We examined bacterial species among 33 phyla, finding some unexpected distribution patterns. RecBCD and addAB are less conserved than recA, with the orthologous recB and addA genes more conserved than the recC or addB genes. We were able to classify RecB vs. AddA and RecC vs. AddB in some bacteria where this had not previously been done. We used logo analysis to identify sequence segments that are conserved, but differ between the RecBC and AddAB proteins, to help future differentiation between members of these two families.
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Affiliation(s)
- Deepti Gurung
- Present address: Department of Cancer Biology, College of Medicine & Life Sciences, The University of Toledo, Toledo OH 43614-1021, USA.,Department of Medical Microbiology & Immunology, and Program in Bioinformatics, College of Medicine & Life Sciences, The University of Toledo, Toledo OH 43614-1021, USA
| | - Robert M Blumenthal
- Department of Medical Microbiology & Immunology, and Program in Bioinformatics, College of Medicine & Life Sciences, The University of Toledo, Toledo OH 43614-1021, USA
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11
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Klimova AN, Sandler SJ. An Epistasis Analysis of recA and recN in Escherichia coli K-12. Genetics 2020; 216:381-393. [PMID: 32816866 PMCID: PMC7536844 DOI: 10.1534/genetics.120.303476] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 08/11/2020] [Indexed: 12/26/2022] Open
Abstract
RecA is essential for double-strand-break repair (DSBR) and the SOS response in Escherichia coli K-12. RecN is an SOS protein and a member of the Structural Maintenance of Chromosomes family of proteins thought to play a role in sister chromatid cohesion/interactions during DSBR. Previous studies have shown that a plasmid-encoded recA4190 (Q300R) mutant had a phenotype similar to ∆recN (mitomycin C sensitive and UV resistant). It was hypothesized that RecN and RecA physically interact, and that recA4190 specifically eliminated this interaction. To test this model, an epistasis analysis between recA4190 and ∆recN was performed in wild-type and recBC sbcBC cells. To do this, recA4190 was first transferred to the chromosome. As single mutants, recA4190 and ∆recN were Rec+ as measured by transductional recombination, but were 3-fold and 10-fold decreased in their ability to do I-SceI-induced DSBR, respectively. In both cases, the double mutant had an additive phenotype relative to either single mutant. In the recBC sbcBC background, recA4190 and ∆recN cells were very UVS (sensitive), Rec-, had high basal levels of SOS expression and an altered distribution of RecA-GFP structures. In all cases, the double mutant had additive phenotypes. These data suggest that recA4190 (Q300R) and ∆recN remove functions in genetically distinct pathways important for DNA repair, and that RecA Q300 was not important for an interaction between RecN and RecA in vivorecA4190 (Q300R) revealed modest phenotypes in a wild-type background and dramatic phenotypes in a recBC sbcBC strain, reflecting greater stringency of RecA's role in that background.
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Affiliation(s)
- Anastasiia N Klimova
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts 01003
| | - Steven J Sandler
- Molecular and Cellular Biology Program, University of Massachusetts Amherst, Massachusetts 01003
- Department of Microbiology, University of Massachusetts Amherst, Massachusetts 01003
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12
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Ojkic N, Lilja E, Direito S, Dawson A, Allen RJ, Waclaw B. A Roadblock-and-Kill Mechanism of Action Model for the DNA-Targeting Antibiotic Ciprofloxacin. Antimicrob Agents Chemother 2020; 64:e02487-19. [PMID: 32601161 PMCID: PMC7449190 DOI: 10.1128/aac.02487-19] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 06/19/2020] [Indexed: 12/19/2022] Open
Abstract
Fluoroquinolones, antibiotics that cause DNA damage by inhibiting DNA topoisomerases, are clinically important, but their mechanism of action is not yet fully understood. In particular, the dynamical response of bacterial cells to fluoroquinolone exposure has hardly been investigated, although the SOS response, triggered by DNA damage, is often thought to play a key role. Here, we investigated the growth inhibition of the bacterium Escherichia coli by the fluoroquinolone ciprofloxacin at low concentrations. We measured the long-term and short-term dynamical response of the growth rate and DNA production rate to ciprofloxacin at both the population and single-cell levels. We show that, despite the molecular complexity of DNA metabolism, a simple roadblock-and-kill model focusing on replication fork blockage and DNA damage by ciprofloxacin-poisoned DNA topoisomerase II (gyrase) quantitatively reproduces long-term growth rates in the presence of ciprofloxacin. The model also predicts dynamical changes in the DNA production rate in wild-type E. coli and in a recombination-deficient mutant following a step-up of ciprofloxacin. Our work highlights that bacterial cells show a delayed growth rate response following fluoroquinolone exposure. Most importantly, our model explains why the response is delayed: it takes many doubling times to fragment the DNA sufficiently to inhibit gene expression. We also show that the dynamical response is controlled by the timescale of DNA replication and gyrase binding/unbinding to the DNA rather than by the SOS response, challenging the accepted view. Our work highlights the importance of including detailed biophysical processes in biochemical-systems models to quantitatively predict the bacterial response to antibiotics.
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Affiliation(s)
- Nikola Ojkic
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
| | - Elin Lilja
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
| | - Susana Direito
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
| | - Angela Dawson
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
| | - Rosalind J Allen
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
- Centre for Synthetic and Systems Biology, Edinburgh, United Kingdom
| | - Bartlomiej Waclaw
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
- Centre for Synthetic and Systems Biology, Edinburgh, United Kingdom
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13
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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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14
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White MA, Darmon E, Lopez-Vernaza MA, Leach DRF. DNA double strand break repair in Escherichia coli perturbs cell division and chromosome dynamics. PLoS Genet 2020; 16:e1008473. [PMID: 31895943 PMCID: PMC6959608 DOI: 10.1371/journal.pgen.1008473] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/14/2020] [Accepted: 12/16/2019] [Indexed: 11/18/2022] Open
Abstract
To prevent the transmission of damaged genomic material between generations, cells require a system for accommodating DNA repair within their cell cycles. We have previously shown that Escherichia coli cells subject to a single, repairable site-specific DNA double-strand break (DSB) per DNA replication cycle reach a new average cell length, with a negligible effect on population growth rate. We show here that this new cell size distribution is caused by a DSB repair-dependent delay in completion of cell division. This delay occurs despite unperturbed cell size regulated initiation of both chromosomal DNA replication and cell division. Furthermore, despite DSB repair altering the profile of DNA replication across the genome, the time required to complete chromosomal duplication is invariant. The delay in completion of cell division is accompanied by a DSB repair-dependent delay in individualization of sister nucleoids. We suggest that DSB repair events create inter-sister connections that persist until those chromosomes are separated by a closing septum.
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Affiliation(s)
- Martin A. White
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, The King’s Buildings, Edinburgh, United Kingdom
- Department of Molecular and Cellular Biology, Harvard University, Cambridge MA, United States of America
| | - Elise Darmon
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, The King’s Buildings, Edinburgh, United Kingdom
| | - Manuel A. Lopez-Vernaza
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, The King’s Buildings, Edinburgh, United Kingdom
| | - David R. F. Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, The King’s Buildings, Edinburgh, United Kingdom
- * E-mail:
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15
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Li C, Danilowicz C, Tashjian TF, Godoy VG, Prévost C, Prentiss M. The positioning of Chi sites allows the RecBCD pathway to suppress some genomic rearrangements. Nucleic Acids Res 2019; 47:1836-1846. [PMID: 30544167 PMCID: PMC6393298 DOI: 10.1093/nar/gky1252] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 11/29/2018] [Accepted: 12/11/2018] [Indexed: 12/03/2022] Open
Abstract
Bacterial recombinational repair of double-strand breaks often begins with creation of initiating 3′ single-stranded DNA (ssDNA) tails on each side of a double-strand break (DSB). Importantly, if the RecBCD pathway is followed, RecBCD creates a gap between the sequences at 3′ ends of the initiating strands. The gap flanks the DSB and extends at least to the nearest Chi site on each strand. Once the initiating strands form ssDNA–RecA filaments, each ssDNA–RecA filament searches for homologous double-stranded DNA (dsDNA) to use as a template for the DNA synthesis needed to fill the gap created by RecBCD. Our experimental results show that the DNA synthesis requires formation of a heteroduplex dsDNA that pairs >20 contiguous bases in the initiating strand with sequence matched bases in a strand from the original dsDNA. To trigger synthesis, the heteroduplex must be near the 3′ end of the initiating strand. Those experimentally determined requirements for synthesis combined with the Chi site dependence of the function of RecBCD and the distribution of Chi sites in bacterial genomes could allow the RecBCD pathway to avoid some genomic rearrangements arising from directly induced DSBs; however, the same three factors could promote other rearrangements.
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Affiliation(s)
- Chastity Li
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | | | - Tommy F Tashjian
- Department of Biology, Northeastern University, Boston, MA 02115, USA
| | - Veronica G Godoy
- Department of Biology, Northeastern University, Boston, MA 02115, USA
| | - Chantal Prévost
- Laboratoire de BioChimie Théorique, CNRS UMR 9080, IBPC, Paris, France
| | - Mara Prentiss
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
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16
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White MA, Azeroglu B, Lopez-Vernaza MA, Hasan AMM, Leach DRF. RecBCD coordinates repair of two ends at a DNA double-strand break, preventing aberrant chromosome amplification. Nucleic Acids Res 2019; 46:6670-6682. [PMID: 29901759 PMCID: PMC6061781 DOI: 10.1093/nar/gky463] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 06/08/2018] [Indexed: 12/23/2022] Open
Abstract
DNA double-strand break (DSB) repair is critical for cell survival. A diverse range of organisms from bacteria to humans rely on homologous recombination for accurate DSB repair. This requires both coordinate action of the two ends of a DSB and stringent control of the resultant DNA replication to prevent unwarranted DNA amplification and aneuploidy. In Escherichia coli, RecBCD enzyme is responsible for the initial steps of homologous recombination. Previous work has revealed recD mutants to be nuclease defective but recombination proficient. Despite this proficiency, we show here that a recD null mutant is defective for the repair of a two-ended DSB and that this defect is associated with unregulated chromosome amplification and defective chromosome segregation. Our results demonstrate that RecBCD plays an important role in avoiding this amplification by coordinating the two recombining ends in a manner that prevents divergent replication forks progressing away from the DSB site.
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Affiliation(s)
- Martin A White
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3FF, UK
| | - Benura Azeroglu
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3FF, UK
| | - Manuel A Lopez-Vernaza
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3FF, UK
| | - A M Mahedi Hasan
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3FF, UK
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3FF, UK
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17
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Lu D, Danilowicz C, Tashjian TF, Prévost C, Godoy VG, Prentiss M. Slow extension of the invading DNA strand in a D-loop formed by RecA-mediated homologous recombination may enhance recognition of DNA homology. J Biol Chem 2019; 294:8606-8616. [PMID: 30975899 PMCID: PMC6544866 DOI: 10.1074/jbc.ra119.007554] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 04/10/2019] [Indexed: 11/21/2022] Open
Abstract
DNA recombination resulting from RecA-mediated strand exchange aided by RecBCD proteins often enables accurate repair of DNA double-strand breaks. However, the process of recombinational repair between short DNA regions of accidental similarity can lead to fatal genomic rearrangements. Previous studies have probed how effectively RecA discriminates against interactions involving a short similar sequence that is embedded in otherwise dissimilar sequences but have not yielded fully conclusive results. Here, we present results of in vitro experiments with fluorescent probes strategically located on the interacting DNA fragments used for recombination. Our findings suggest that DNA synthesis increases the stability of the recombination products. Fluorescence measurements can also probe the homology dependence of the extension of invading DNA strands in D-loops formed by RecA-mediated strand exchange. We examined the slow extension of the invading strand in a D-loop by DNA polymerase (Pol) IV and the more rapid extension by DNA polymerase LF-Bsu. We found that when DNA Pol IV extends the invading strand in a D-loop formed by RecA-mediated strand exchange, the extension afforded by 82 bp of homology is significantly longer than the extension on 50 bp of homology. In contrast, the extension of the invading strand in D-loops by DNA LF-Bsu Pol is similar for intermediates with ≥50 bp of homology. These results suggest that fatal genomic rearrangements due to the recombination of small regions of accidental homology may be reduced if RecA-mediated strand exchange is immediately followed by DNA synthesis by a slow polymerase.
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Affiliation(s)
- Daniel Lu
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138
| | - Claudia Danilowicz
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138
| | - Tommy F Tashjian
- Department of Biology, Northeastern University, Boston, Massachusetts 02115
| | - Chantal Prévost
- Laboratoire de Biochimie Théorique, CNRS UMR 9080, Institut de Biologie Physico-chimique (IBPC), Paris 75005, France
| | - Veronica G Godoy
- Department of Biology, Northeastern University, Boston, Massachusetts 02115
| | - Mara Prentiss
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138.
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18
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Makrantoni V, Robertson D, Marston AL. Analysis of the Chromosomal Localization of Yeast SMC Complexes by Chromatin Immunoprecipitation. Methods Mol Biol 2019; 2004:119-138. [PMID: 31147914 PMCID: PMC7115940 DOI: 10.1007/978-1-4939-9520-2_10] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A plethora of biological processes like gene transcription, DNA replication, DNA recombination, and chromosome segregation are mediated through protein-DNA interactions. A powerful method for investigating proteins within a native chromatin environment in the cell is chromatin immunoprecipitation (ChIP). Combined with the recent technological advancement in next generation sequencing, the ChIP assay can map the exact binding sites of a protein of interest across the entire genome. Here we describe a-step-by step protocol for ChIP followed by library preparation for ChIP-seq from yeast cells.
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Affiliation(s)
- Vasso Makrantoni
- The Wellcome Centre for Cell Biology, Institute of Cell Biology, School of Biological Sciences, Michael Swann Building, Max Born Crescent, Edinburgh, EH9 3BF UK
| | - Daniel Robertson
- The Wellcome Centre for Cell Biology, Institute of Cell Biology, School of Biological Sciences, Michael Swann Building, Max Born Crescent, Edinburgh, EH9 3BF UK
| | - Adele L. Marston
- The Wellcome Centre for Cell Biology, Institute of Cell Biology, School of Biological Sciences, Michael Swann Building, Max Born Crescent, Edinburgh, EH9 3BF UK,To whom correspondence should be addressed:
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19
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Hasan AMM, Azeroglu B, Leach DRF. Genomic Analysis of DNA Double-Strand Break Repair in Escherichia coli. Methods Enzymol 2018; 612:523-554. [PMID: 30502957 DOI: 10.1016/bs.mie.2018.09.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Counting DNA whole genome sequencing reads is providing new insight into DNA double-strand break repair (DSBR) in the model organism Escherichia coli. We describe the application of RecA chromatin immunoprecipitation coupled to genomic DNA sequencing (RecA-ChIP-seq) and marker frequency analysis (MFA) to analyze the genomic consequences of DSBR. We provide detailed procedures for the preparation of DNA and the analysis of data. We compare different ways of visualizing ChIP data and show that alternative protocols for the preparation of DNA for MFA differentially affect the recovery of branched DNA molecules containing Holliday junctions.
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Affiliation(s)
- A M Mahedi Hasan
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh, United Kingdom
| | - Benura Azeroglu
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh, United Kingdom
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh, United Kingdom.
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20
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Sivaramakrishnan P, Gordon AJE, Halliday JA, Herman C. How Acts of Infidelity Promote DNA Break Repair: Collision and Collusion Between DNA Repair and Transcription. Bioessays 2018; 40:e1800045. [PMID: 30091472 PMCID: PMC6334755 DOI: 10.1002/bies.201800045] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 07/07/2018] [Indexed: 12/20/2022]
Abstract
Transcription is a fundamental cellular process and the first step in gene regulation. Although RNA polymerase (RNAP) is highly processive, in growing cells the progression of transcription can be hindered by obstacles on the DNA template, such as damaged DNA. The authors recent findings highlight a trade-off between transcription fidelity and DNA break repair. While a lot of work has focused on the interaction between transcription and nucleotide excision repair, less is known about how transcription influences the repair of DNA breaks. The authors suggest that when the cell experiences stress from DNA breaks, the control of RNAP processivity affects the balance between preserving transcription integrity and DNA repair. Here, how the conflict between transcription and DNA double-strand break (DSB) repair threatens the integrity of both RNA and DNA are discussed. In reviewing this field, the authors speculate on cellular paradigms where this equilibrium is well sustained, and instances where the maintenance of transcription fidelity is favored over genome stability.
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Affiliation(s)
- Priya Sivaramakrishnan
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Alasdair J E Gordon
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jennifer A Halliday
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Christophe Herman
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Baylor College of Medicine, Dan L. Duncan Comprehensive Cancer Center, Houston, TX 77030, USA
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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21
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Topoisomerases I and III inhibit R-loop formation to prevent unregulated replication in the chromosomal Ter region of Escherichia coli. PLoS Genet 2018; 14:e1007668. [PMID: 30222737 PMCID: PMC6160223 DOI: 10.1371/journal.pgen.1007668] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 09/27/2018] [Accepted: 08/29/2018] [Indexed: 02/07/2023] Open
Abstract
Type 1A topoisomerases (topos) are the only ubiquitous topos. E. coli has two type 1A topos, topo I (topA) and topo III (topB). Topo I relaxes negative supercoiling in part to inhibit R-loop formation. To grow, topA mutants acquire compensatory mutations, base substitutions in gyrA or gyrB (gyrase) or amplifications of a DNA region including parC and parE (topo IV). topB mutants grow normally and topo III binds tightly to single-stranded DNA. What functions topo I and III share in vivo and how cells lacking these important enzymes can survive is unclear. Previously, a gyrB(Ts) compensatory mutation was used to construct topA topB null mutants. These mutants form very long filaments and accumulate diffuse DNA, phenotypes that appears to be related to replication from R-loops. Here, next generation sequencing and qPCR for marker frequency analysis were used to further define the functions of type 1A topos. The results reveal the presence of a RNase HI-sensitive origin of replication in the terminus (Ter) region of the chromosome that is more active in topA topB cells than in topA and rnhA (RNase HI) null cells. The S9.6 antibodies specific to DNA:RNA hybrids were used in dot-blot experiments to show the accumulation of R-loops in rnhA, topA and topA topB null cells. Moreover topA topB gyrB(Ts) strains, but not a topA gyrB(Ts) strain, were found to carry a parC parE amplification. When a topA gyrB(Ts) mutant carried a plasmid producing topo IV, topB null transductants did not have parC parE amplifications. Altogether, the data indicate that in E. coli type 1A topos are required to inhibit R-loop formation/accumulation mostly to prevent unregulated replication in Ter, and that they are essential to prevent excess negative supercoiling and its detrimental effects on cell growth and survival. DNA topoisomerases are nicking closing enzymes with strand passage activity that solves the topological problems inherent to the double-helical structure of DNA. Topos of the type 1A family are the only ubiquitous topos. They are classified in two subfamilies, topo I and topo III respectively found in bacteria only and in organisms from the three domains of life. The prototype enzymes of these two subfamilies are topo I and topo III from Escherichia coli. Recent data suggest that duplications leading to topo I and III subfamilies occurred in the Last Common Universal Ancestor of the three domains of life. In this context, our finding reported here that both E. coli topo I and III control R-loop formation/accumulation, mostly to inhibit unregulated replication, may suggest that R-loops have been a problem early in the evolution of life. Furthermore, our data show that E. coli cells can survive in the absence of type 1A topos, owing to the surproduction of topo IV that can relax excess negative supercoiling and prevent R-loop formation. Thus, our results strongly suggest that a major function of type 1A topos is to control R-loop formation to preserve the integrity of the genome.
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22
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Ghotaslou R, Bannazadeh Baghi H, Alizadeh N, Yekani M, Arbabi S, Memar MY. Mechanisms of Bacteroides fragilis resistance to metronidazole. INFECTION GENETICS AND EVOLUTION 2018; 64:156-163. [PMID: 29936037 DOI: 10.1016/j.meegid.2018.06.020] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Revised: 06/09/2018] [Accepted: 06/16/2018] [Indexed: 01/01/2023]
Abstract
Metronidazole-resistant Bacteroides fragilis (B. fragilis) have been reported worldwide. Several mechanisms contribute to B. fragilis resistance to metronidazole. In some cases, the mechanisms of metronidazole resistance are unknown. Understanding the mechanisms of resistance is important for therapy, the design of new alternative drugs, and control of resistant strains. In this study, a comprehensive review of the B. fragilis resistance mechanisms to metronidazole was prepared. The rate of metronidazole-resistant B. fragilis has been reported as ranging from 0.5% to 7.8% in many surveys. According to CLSI, isolates with MICs ≥32 μg/mL are considered to be metronidazole-resistant. In the majority of cases, metronidazole resistance in B. fragilis is coupled with the existence of nim genes. Metronidazole resistance could be induced in nim-negative strains by exposure to sub-MIC levels of metronidazole. There are multi-drug efflux pumps in B. fragilis which can pump out a variety of substrates such as metronidazole. The recA overexpression and deficiency of feoAB are other reported metronidazole resistance mechanisms in this bacterium.
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Affiliation(s)
- Reza Ghotaslou
- The Liver and Gastrointestinal Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Department of Microbiology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Hossein Bannazadeh Baghi
- Department of Microbiology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran; Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Naser Alizadeh
- Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Students' Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Mina Yekani
- Department of Microbiology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran; Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Shahram Arbabi
- The Liver and Gastrointestinal Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Department of Microbiology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Mohammad Yousef Memar
- Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Students' Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran.
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23
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Amarh V, White MA, Leach DRF. Dynamics of RecA-mediated repair of replication-dependent DNA breaks. J Cell Biol 2018; 217:2299-2307. [PMID: 29789437 PMCID: PMC6028544 DOI: 10.1083/jcb.201803020] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 04/27/2018] [Accepted: 04/30/2018] [Indexed: 11/22/2022] Open
Abstract
Spontaneous DNA double-strand breaks form during DNA replication and are largely repaired by recombination with a sister chromosome. Using live-cell fluorescence imaging, Amarh et al. show that repair of a replication-dependent break is rapid, localized, and involves a transient RecA focus. Chromosomal replication is the major source of spontaneous DNA double-strand breaks (DSBs) in living cells. Repair of these DSBs is essential for cell viability, and accuracy of repair is critical to avoid chromosomal rearrangements. Repair of replication-dependent DSBs occurs primarily by homologous recombination with a sister chromosome. However, this reaction has never been visualized at a defined chromosomal locus, so little is known about its spatial or temporal dynamics. Repair of a replication-independent DSB generated in Escherichia coli by a rare-cutting endonuclease leads to the formation of a bundle of RecA filaments. In this study, we show that in contrast, repair of a replication-dependent DSB involves a transient RecA focus localized in the central region of the cell in which the DNA is replicated. The recombining loci remain centrally located with restricted movement before segregating with little extension to the period of postreplicative sister-chromosome cohesion. The spatial and temporal efficiency of this reaction is remarkable.
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Affiliation(s)
- Vincent Amarh
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, Scotland, UK
| | - Martin A White
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, Scotland, UK
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, Scotland, UK
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24
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The transcription fidelity factor GreA impedes DNA break repair. Nature 2017; 550:214-218. [PMID: 28976965 PMCID: PMC5654330 DOI: 10.1038/nature23907] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 08/07/2017] [Indexed: 01/07/2023]
Abstract
Homologous recombination repairs DNA double-strand breaks and must function even on actively transcribed DNA. Because break repair prevents chromosome loss, the completion of repair is expected to outweigh the transcription of broken templates. Yet, the interplay between DNA break repair and transcription processivity is unclear. Here we show that the transcription factor GreA inhibits break repair in Escherichia coli. GreA restarts backtracked RNA polymerase (RNAP) and hence promotes transcription fidelity. We report that removal of GreA results in dramatically enhanced break repair via the classical RecBCD-RecA pathway. Using a deep-sequencing method to measure chromosomal exonucleolytic degradation (XO-Seq), we demonstrate that the absence of GreA limits RecBCD-mediated resection. Our findings suggest that increased RNAP backtracking promotes break repair by instigating RecA loading by RecBCD, without the influence of canonical Chi signals. The idea that backtracked RNAP can stimulate recombination presents a DNA transaction conundrum: a transcription fidelity factor compromises genomic integrity.
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25
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Division-induced DNA double strand breaks in the chromosome terminus region of Escherichia coli lacking RecBCD DNA repair enzyme. PLoS Genet 2017; 13:e1006895. [PMID: 28968392 PMCID: PMC5638614 DOI: 10.1371/journal.pgen.1006895] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 10/12/2017] [Accepted: 06/23/2017] [Indexed: 12/27/2022] Open
Abstract
Marker frequency analysis of the Escherichia coli recB mutant chromosome has revealed a deficit of DNA in a specific zone of the terminus, centred on the dif/TerC region. Using fluorescence microscopy of a marked chromosomal site, we show that the dif region is lost after replication completion, at the time of cell division, in one daughter cell only, and that the phenomenon is transmitted to progeny. Analysis by marker frequency and microscopy shows that the position of DNA loss is not defined by the replication fork merging point since it still occurs in the dif/TerC region when the replication fork trap is displaced in strains harbouring ectopic Ter sites. Terminus DNA loss in the recB mutant is also independent of dimer resolution by XerCD at dif and of Topo IV action close to dif. It occurs in the terminus region, at the point of inversion of the GC skew, which is also the point of convergence of specific sequence motifs like KOPS and Chi sites, regardless of whether the convergence of GC skew is at dif (wild-type) or a newly created sequence. In the absence of FtsK-driven DNA translocation, terminus DNA loss is less precisely targeted to the KOPS convergence sequence, but occurs at a similar frequency and follows the same pattern as in FtsK+ cells. Importantly, using ftsIts, ftsAts division mutants and cephalexin treated cells, we show that DNA loss of the dif region in the recB mutant is decreased by the inactivation of cell division. We propose that it results from septum-induced chromosome breakage, and largely contributes to the low viability of the recB mutant. RecBCD protein complex is an important player of DSB repair in bacteria and bacteria that cannot repair DNA double-stranded breaks (DSB) have a low viability. Whole genome sequencing analyses showed a deficit in specific sequences of the chromosome terminus region in recB mutant cells, suggesting terminus DNA degradation during growth. We studied here the phenomenon of terminus DNA loss by whole genome sequencing and microscopy analyses of exponentially growing bacteria. We tested all processes known to take place in the chromosome terminus region for a putative role in DNA loss: replication fork termination, dimer resolution, resolution of catenated chromosomes, and translocation of the chromosome arms in daughter cells during septum formation. None of the mutations that affect these processes prevents the phenomenon. However, we observed that terminus DNA loss is abolished in cells that cannot divide. We propose that in cells defective for RecBCD-mediated DSB repair the terminus region of the chromosome remains in the way of the growing septum during cell division, then septum closure triggers chromosome breakage and, in turn, DNA degradation.
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Abstract
In this review, we discuss how two evolutionarily conserved pathways at the interface of DNA replication and repair, template switching and break-induced replication, lead to the deleterious large-scale expansion of trinucleotide DNA repeats that cause numerous hereditary diseases. We highlight that these pathways, which originated in prokaryotes, may be subsequently hijacked to maintain long DNA microsatellites in eukaryotes. We suggest that the negative mutagenic outcomes of these pathways, exemplified by repeat expansion diseases, are likely outweighed by their positive role in maintaining functional repetitive regions of the genome such as telomeres and centromeres.
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Affiliation(s)
| | - Jane C Kim
- Department of Biological Sciences, California State University San Marcos, San Marcos, CA, USA
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Badrinarayanan A, Le TBK, Spille JH, Cisse II, Laub MT. Global analysis of double-strand break processing reveals in vivo properties of the helicase-nuclease complex AddAB. PLoS Genet 2017; 13:e1006783. [PMID: 28489851 PMCID: PMC5443536 DOI: 10.1371/journal.pgen.1006783] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 05/24/2017] [Accepted: 04/26/2017] [Indexed: 12/03/2022] Open
Abstract
In bacteria, double-strand break (DSB) repair via homologous recombination is thought to be initiated through the bi-directional degradation and resection of DNA ends by a helicase-nuclease complex such as AddAB. The activity of AddAB has been well-studied in vitro, with translocation speeds between 400–2000 bp/s on linear DNA suggesting that a large section of DNA around a break site is processed for repair. However, the translocation rate and activity of AddAB in vivo is not known, and how AddAB is regulated to prevent excessive DNA degradation around a break site is unclear. To examine the functions and mechanistic regulation of AddAB inside bacterial cells, we developed a next-generation sequencing-based approach to assay DNA processing after a site-specific DSB was introduced on the chromosome of Caulobacter crescentus. Using this assay we determined the in vivo rates of DSB processing by AddAB and found that putative chi sites attenuate processing in a RecA-dependent manner. This RecA-mediated regulation of AddAB prevents the excessive loss of DNA around a break site, limiting the effects of DSB processing on transcription. In sum, our results, taken together with prior studies, support a mechanism for regulating AddAB that couples two key events of DSB repair–the attenuation of DNA-end processing and the initiation of homology search by RecA–thereby helping to ensure that genomic integrity is maintained during DSB repair. Double-strand breaks (DSBs) are a threat to genome integrity and are faithfully repaired via homologous recombination. The initial processing of DSB ends that prepares them for recombination has been well-studied in vitro, but is less well characterized in vivo. We describe a deep sequencing-based assay for assessing the early steps of DSB processing in bacterial cells by the helicase-nuclease complex AddAB. We find that a combination of chi site recognition and RecA loading is required to attenuate AddAB activity. In the absence of RecA, the chromosome is excessively degraded with a concomitant loss in transcription. Our results, along with prior studies, support a model for how chi recognition and RecA together regulate AddAB to maintain genome integrity and facilitate recombination.
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Affiliation(s)
- Anjana Badrinarayanan
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States of America
- National Centre for Biological Sciences (NCBS), Tata Institute of Fundamental Research, Bangalore, India
| | - Tung B. K. Le
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States of America
- Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom
| | - Jan-Hendrik Spille
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, United States of America
| | - Ibrahim I. Cisse
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, United States of America
| | - Michael T. Laub
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States of America
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, United States of America
- * E-mail:
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28
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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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Taylor AF, Amundsen SK, Smith GR. Unexpected DNA context-dependence identifies a new determinant of Chi recombination hotspots. Nucleic Acids Res 2016; 44:8216-28. [PMID: 27330137 PMCID: PMC5041463 DOI: 10.1093/nar/gkw541] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 06/03/2016] [Indexed: 11/23/2022] Open
Abstract
Homologous recombination occurs especially frequently near special chromosomal sites called hotspots. In Escherichia coli, Chi hotspots control RecBCD enzyme, a protein machine essential for the major pathway of DNA break-repair and recombination. RecBCD generates recombinogenic single-stranded DNA ends by unwinding DNA and cutting it a few nucleotides to the 3′ side of 5′ GCTGGTGG 3′, the sequence historically equated with Chi. To test if sequence context affects Chi activity, we deep-sequenced the products of a DNA library containing 10 random base-pairs on each side of the Chi sequence and cut by purified RecBCD. We found strongly enhanced cutting at Chi with certain preferred sequences, such as A or G at nucleotides 4–7, on the 3′ flank of the Chi octamer. These sequences also strongly increased Chi hotspot activity in E. coli cells. Our combined enzymatic and genetic results redefine the Chi hotspot sequence, implicate the nuclease domain in Chi recognition, indicate that nicking of one strand at Chi is RecBCD's biologically important reaction in living cells, and enable more precise analysis of Chi's role in recombination and genome evolution.
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Affiliation(s)
- Andrew F Taylor
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA
| | - Susan K Amundsen
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA
| | - Gerald R Smith
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA
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30
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Bell JC, Kowalczykowski SC. RecA: Regulation and Mechanism of a Molecular Search Engine. Trends Biochem Sci 2016; 41:491-507. [PMID: 27156117 PMCID: PMC4892382 DOI: 10.1016/j.tibs.2016.04.002] [Citation(s) in RCA: 143] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Revised: 04/04/2016] [Accepted: 04/05/2016] [Indexed: 11/19/2022]
Abstract
Homologous recombination maintains genomic integrity by repairing broken chromosomes. The broken chromosome is partially resected to produce single-stranded DNA (ssDNA) that is used to search for homologous double-stranded DNA (dsDNA). This homology driven 'search and rescue' is catalyzed by a class of DNA strand exchange proteins that are defined in relation to Escherichia coli RecA, which forms a filament on ssDNA. Here, we review the regulation of RecA filament assembly and the mechanism by which RecA quickly and efficiently searches for and identifies a unique homologous sequence among a vast excess of heterologous DNA. Given that RecA is the prototypic DNA strand exchange protein, its behavior affords insight into the actions of eukaryotic RAD51 orthologs and their regulators, BRCA2 and other tumor suppressors.
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Affiliation(s)
- Jason C Bell
- Department of Microbiology and Molecular Genetics and Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Stephen C Kowalczykowski
- Department of Microbiology and Molecular Genetics and Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
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31
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Pagès V. Single-strand gap repair involves both RecF and RecBCD pathways. Curr Genet 2016; 62:519-21. [PMID: 26874520 DOI: 10.1007/s00294-016-0575-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 02/01/2016] [Accepted: 02/03/2016] [Indexed: 10/22/2022]
Abstract
Homologous recombination repairs discontinuities in DNA including single-strand gaps (SSGs) and double-strand breaks (DSBs). This commentary describes how the RecBCD and RecF pathways might be exchangeable for the repair of their respective DSB and SSG canonical substrates. In particular, I will discuss how the RecBCD pathway could engage in the repair of an SSG even when the latter is not associated with a DSB.
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Affiliation(s)
- Vincent Pagès
- Cancer Research Center of Marseille, Team DNA Damage Tolerance, CNRS, UMR7258, 13009, Marseille, France. .,Inserm, U1068, 13009, Marseille, France. .,Institut Paoli-Calmettes, 13009, Marseille, France. .,Aix-Marseille University, UM 105, 13284, Marseille, France.
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32
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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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