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Wang P, Ma Y, Li J, Su J, Chi J, Zhu X, Zhu X, Zhang C, Bi C, Zhang X. Exploring the De Novo NMN Biosynthesis as an Alternative Pathway to Enhance NMN Production. ACS Synth Biol 2024; 13:2425-2435. [PMID: 39023319 DOI: 10.1021/acssynbio.4c00115] [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] [Indexed: 07/20/2024]
Abstract
Nicotinamide mononucleotide (NMN) serves as a precursor for NAD+ synthesis and has been shown to have positive effects on the human body. Previous research has predominantly focused on the nicotinamide phosphoribosyltransferase-mediated route (NadV-mediated route) for NMN biosynthesis. In this study, we have explored the de novo NMN biosynthesis route as an alternative pathway to enhance NMN production. Initially, we systematically engineered Escherichia coli to enhance its capacity for NMN synthesis and accumulation, resulting in a remarkable over 100-fold increase in NMN yield. Subsequently, we progressively enhanced the de novo NMN biosynthesis route to further augment NMN production. We screened and identified the crucial role of MazG in catalyzing the enzymatic cleavage of NAD+ to NMN. And the de novo NMN biosynthesis route was optimized and integrated with the NadV-mediated NMN biosynthetic pathways, leading to an intracellular concentration of 844.10 ± 17.40 μM NMN. Furthermore, the introduction of two transporters enhanced the uptake of NAM and the excretion of NMN, resulting in NMN production of 1293.73 ± 61.38 μM. Finally, by engineering an E. coli strain with optimized PRPP synthetase, we achieved the highest NMN production, reaching 3067.98 ± 27.25 μM after 24 h of fermentation at the shake flask level. In addition to constructing an efficient E. coli cell factory for NMN production, our findings provide new insights into understanding the NAD+ salvage pathway and its role in energy metabolism within E. coli.
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Affiliation(s)
- Pengju Wang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Yidan Ma
- School of Biological Engineering, Dalian Polytechnic University, Dalian 116034, China
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Ju Li
- College of Life Science, Tianjin Normal University, Tianjin 300382, China
| | - Junchang Su
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Junxi Chi
- School of Biological Engineering, Dalian Polytechnic University, Dalian 116034, China
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Xingmiao Zhu
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Xinna Zhu
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Chunzhi Zhang
- School of Biological Engineering, Dalian Polytechnic University, Dalian 116034, China
| | - Changhao Bi
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
| | - Xueli Zhang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China
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2
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Łazowski K, Woodgate R, Fijalkowska IJ. Escherichia coli DNA replication: the old model organism still holds many surprises. FEMS Microbiol Rev 2024; 48:fuae018. [PMID: 38982189 PMCID: PMC11253446 DOI: 10.1093/femsre/fuae018] [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: 05/09/2024] [Revised: 06/26/2024] [Accepted: 07/08/2024] [Indexed: 07/11/2024] Open
Abstract
Research on Escherichia coli DNA replication paved the groundwork for many breakthrough discoveries with important implications for our understanding of human molecular biology, due to the high level of conservation of key molecular processes involved. To this day, it attracts a lot of attention, partially by virtue of being an important model organism, but also because the understanding of factors influencing replication fidelity might be important for studies on the emergence of antibiotic resistance. Importantly, the wide access to high-resolution single-molecule and live-cell imaging, whole genome sequencing, and cryo-electron microscopy techniques, which were greatly popularized in the last decade, allows us to revisit certain assumptions about the replisomes and offers very detailed insight into how they work. For many parts of the replisome, step-by-step mechanisms have been reconstituted, and some new players identified. This review summarizes the latest developments in the area, focusing on (a) the structure of the replisome and mechanisms of action of its components, (b) organization of replisome transactions and repair, (c) replisome dynamics, and (d) factors influencing the base and sugar fidelity of DNA synthesis.
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Affiliation(s)
- Krystian Łazowski
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
| | - Roger Woodgate
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, United States
| | - Iwona J Fijalkowska
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
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3
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Bugallo A, Sánchez M, Fernández-García M, Segurado M. S-phase checkpoint prevents leading strand degradation from strand-associated nicks at stalled replication forks. Nucleic Acids Res 2024; 52:5121-5137. [PMID: 38520409 PMCID: PMC11109941 DOI: 10.1093/nar/gkae192] [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: 11/06/2023] [Revised: 03/01/2024] [Accepted: 03/07/2024] [Indexed: 03/25/2024] Open
Abstract
The S-phase checkpoint is involved in coupling DNA unwinding with nascent strand synthesis and is critical to maintain replication fork stability in conditions of replicative stress. However, its role in the specific regulation of leading and lagging strands at stalled forks is unclear. By conditionally depleting RNaseH2 and analyzing polymerase usage genome-wide, we examine the enzymology of DNA replication during a single S-phase in the presence of replicative stress and show that there is a differential regulation of lagging and leading strands. In checkpoint proficient cells, lagging strand replication is down-regulated through an Elg1-dependent mechanism. Nevertheless, when checkpoint function is impaired we observe a defect specifically at the leading strand, which was partially dependent on Exo1 activity. Further, our genome-wide mapping of DNA single-strand breaks reveals that strand discontinuities highly accumulate at the leading strand in HU-treated cells, whose dynamics are affected by checkpoint function and Exo1 activity. Our data reveal an unexpected role of Exo1 at the leading strand and support a model of fork stabilization through prevention of unrestrained Exo1-dependent resection of leading strand-associated nicks after fork stalling.
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Affiliation(s)
- Alberto Bugallo
- Instituto de Biología Funcional y Genómica (CSIC/USAL), Campus Miguel de Unamuno, Salamanca 37007, Spain
| | - Mar Sánchez
- Instituto de Biología Funcional y Genómica (CSIC/USAL), Campus Miguel de Unamuno, Salamanca 37007, Spain
| | - María Fernández-García
- Instituto de Biología Funcional y Genómica (CSIC/USAL), Campus Miguel de Unamuno, Salamanca 37007, Spain
| | - Mónica Segurado
- Instituto de Biología Funcional y Genómica (CSIC/USAL), Campus Miguel de Unamuno, Salamanca 37007, Spain
- Departamento de Microbiología y Genética (USAL), Campus Miguel de Unamuno, Salamanca 37007, Spain
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4
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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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5
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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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6
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Cherry ME, Dubiel K, Henry C, Wood EA, Revitt-Mills SA, Keck JL, Cox MM, van Oijen AM, Ghodke H, Robinson A. Spatiotemporal Dynamics of Single-stranded DNA Intermediates in Escherichia coli. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.08.539320. [PMID: 37214928 PMCID: PMC10197600 DOI: 10.1101/2023.05.08.539320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Single-stranded DNA gaps form within the E. coli chromosome during replication, repair and recombination. However, information about the extent of ssDNA creation in the genome is limited. To complement a recent whole-genome sequencing study revealing ssDNA gap genomic distribution, size, and frequency, we used fluorescence microscopy to monitor the spatiotemporal dynamics of single-stranded DNA within live E. coli cells. The ssDNA was marked by a functional fluorescent protein fusion of the SSB protein that replaces the wild type SSB. During log-phase growth the SSB fusion produces a mixture of punctate foci and diffuse fluorescence spread throughout the cytosol. Many foci are clustered. Fluorescent markers of DNA polymerase III frequently co-localize with SSB foci, often localizing to the outer edge of the large SSB features. Novel SSB-enriched features form and resolve regularly during normal growth. UV irradiation induces a rapid increase in SSB foci intensity and produces large features composed of multiple partially overlapping foci. The results provide a critical baseline for further exploration of ssDNA generation during DNA metabolism. Alterations in the patterns seen in a mutant lacking RecB function tentatively suggest associations of particular SSB features with the repair of double strand breaks and post-replication gaps.
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Łazowski K, Faraz M, Vaisman A, Ashton NW, Jonczyk P, Fijalkowska IJ, Clausen AR, Woodgate R, Makiela-Dzbenska K. Strand specificity of ribonucleotide excision repair in Escherichia coli. Nucleic Acids Res 2023; 51:1766-1782. [PMID: 36762476 PMCID: PMC9976901 DOI: 10.1093/nar/gkad038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 01/03/2023] [Accepted: 01/12/2023] [Indexed: 02/11/2023] Open
Abstract
In Escherichia coli, replication of both strands of genomic DNA is carried out by a single replicase-DNA polymerase III holoenzyme (pol III HE). However, in certain genetic backgrounds, the low-fidelity TLS polymerase, DNA polymerase V (pol V) gains access to undamaged genomic DNA where it promotes elevated levels of spontaneous mutagenesis preferentially on the lagging strand. We employed active site mutants of pol III (pol IIIα_S759N) and pol V (pol V_Y11A) to analyze ribonucleotide incorporation and removal from the E. coli chromosome on a genome-wide scale under conditions of normal replication, as well as SOS induction. Using a variety of methods tuned to the specific properties of these polymerases (analysis of lacI mutational spectra, lacZ reversion assay, HydEn-seq, alkaline gel electrophoresis), we present evidence that repair of ribonucleotides from both DNA strands in E. coli is unequal. While RNase HII plays a primary role in leading-strand Ribonucleotide Excision Repair (RER), the lagging strand is subject to other repair systems (RNase HI and under conditions of SOS activation also Nucleotide Excision Repair). Importantly, we suggest that RNase HI activity can also influence the repair of single ribonucleotides incorporated by the replicase pol III HE into the lagging strand.
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Affiliation(s)
- Krystian Łazowski
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Mahmood Faraz
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg 40530, Sweden
| | - Alexandra Vaisman
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA
| | - Nicholas W Ashton
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA
| | - Piotr Jonczyk
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Iwona J Fijalkowska
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Anders R Clausen
- Department of Medical Biochemistry and Cell Biology, University of Gothenburg, Gothenburg 40530, Sweden
| | - Roger Woodgate
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA
| | - Karolina Makiela-Dzbenska
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
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Fujita H, Osaku A, Sakane Y, Yoshida K, Yamada K, Nara S, Mukai T, Su’etsugu M. Enzymatic Supercoiling of Bacterial Chromosomes Facilitates Genome Manipulation. ACS Synth Biol 2022; 11:3088-3099. [PMID: 35998348 PMCID: PMC9486964 DOI: 10.1021/acssynbio.2c00353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The physical stability of bacterial chromosomes is important for their in vitro manipulation, while genetic stability is important in vivo. However, extracted naked chromosomes in the open circular form are fragile due to nicks and gaps. Using a nick/gap repair and negative supercoiling reaction (named SCR), we first achieved the negative supercoiling of the whole genomes extracted from Escherichia coli and Vibrio natriegens cells. Supercoiled chromosomes of 0.2-4.6 megabase (Mb) were separated by size using a conventional agarose gel electrophoresis and served as DNA size markers. We also achieved the enzymatic replication of 1-2 Mb chromosomes using the reconstituted E. coli replication-cycle reaction (RCR). Electroporation-ready 1 Mb chromosomes were prepared by a modified SCR performed at a low salt concentration (L-SCR) and directly introduced into commercial electrocompetent E. coli cells. Since successful electroporation relies on the genetic stability of a chromosome in cells, genetically stable 1 Mb chromosomes were developed according to a portable chromosome format (PCF). Using physically and genetically stabilized chromosomes, the democratization of genome synthetic biology will be greatly accelerated.
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9
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McLean EK, Nye TM, Lowder FC, Simmons LA. The Impact of RNA-DNA Hybrids on Genome Integrity in Bacteria. Annu Rev Microbiol 2022; 76:461-480. [PMID: 35655343 PMCID: PMC9527769 DOI: 10.1146/annurev-micro-102521-014450] [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] [Indexed: 09/10/2023]
Abstract
During the essential processes of DNA replication and transcription, RNA-DNA hybrid intermediates are formed that pose significant risks to genome integrity when left unresolved. To manage RNA-DNA hybrids, all cells rely on RNase H family enzymes that specifically cleave the RNA portion of the many different types of hybrids that form in vivo. Recent experimental advances have provided new insight into how RNA-DNA hybrids form and the consequences to genome integrity that ensue when persistent hybrids remain unresolved. Here we review the types of RNA-DNA hybrids, including R-loops, RNA primers, and ribonucleotide misincorporations, that form during DNA replication and transcription and discuss how each type of hybrid can contribute to genome instability in bacteria. Further, we discuss how bacterial RNase HI, HII, and HIII and bacterial FEN enzymes contribute to genome maintenance through the resolution of hybrids.
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Affiliation(s)
- Emma K McLean
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA;
| | - Taylor M Nye
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA;
- Current affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Frances C Lowder
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA;
| | - Lyle A Simmons
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA;
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Pham P, Shao Y, Cox MM, Goodman MF. Genomic landscape of single-stranded DNA gapped intermediates in Escherichia coli. Nucleic Acids Res 2021; 50:937-951. [PMID: 34951472 PMCID: PMC8789085 DOI: 10.1093/nar/gkab1269] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 12/08/2021] [Accepted: 12/13/2021] [Indexed: 12/22/2022] Open
Abstract
Single-stranded (ss) gapped regions in bacterial genomes (gDNA) are formed on W- and C-strands during replication, repair, and recombination. Using non-denaturing bisulfite treatment to convert C to U on ssDNA, combined with deep sequencing, we have mapped gDNA gap locations, sizes, and distributions in Escherichia coli for cells grown in mid-log phase in the presence and absence of UV irradiation, and in stationary phase cells. The fraction of ssDNA on gDNA is similar for W- and C-strands, ∼1.3% for log phase cells, ∼4.8% for irradiated log phase cells, and ∼8.5% for stationary phase cells. After UV irradiation, gaps increased in numbers and average lengths. A monotonic reduction in ssDNA occurred symmetrically between the DNA replication origin of (OriC) and terminus (Ter) for log phase cells with and without UV, a hallmark feature of DNA replication. Stationary phase cells showed no OriC → Ter ssDNA gradient. We have identified a spatially diverse gapped DNA landscape containing thousands of highly enriched ‘hot’ ssDNA regions along with smaller numbers of ‘cold’ regions. This analysis can be used for a wide variety of conditions to map ssDNA gaps generated when DNA metabolic pathways have been altered, and to identify proteins bound in the gaps.
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Affiliation(s)
- Phuong Pham
- Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089-2910, USA
| | - Yijun Shao
- Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089-2910, 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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11
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Leroux M, Soubry N, Reyes-Lamothe R. Dynamics of Proteins and Macromolecular Machines in Escherichia coli. EcoSal Plus 2021; 9:eESP00112020. [PMID: 34060908 PMCID: PMC11163846 DOI: 10.1128/ecosalplus.esp-0011-2020] [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: 01/25/2021] [Accepted: 03/16/2021] [Indexed: 11/20/2022]
Abstract
Proteins are major contributors to the composition and the functions in the cell. They often assemble into larger structures, macromolecular machines, to carry out intricate essential functions. Although huge progress in understanding how macromolecular machines function has been made by reconstituting them in vitro, the role of the intracellular environment is still emerging. The development of fluorescence microscopy techniques in the last 2 decades has allowed us to obtain an increased understanding of proteins and macromolecular machines in cells. Here, we describe how proteins move by diffusion, how they search for their targets, and how they are affected by the intracellular environment. We also describe how proteins assemble into macromolecular machines and provide examples of how frequent subunit turnover is used for them to function and to respond to changes in the intracellular conditions. This review emphasizes the constant movement of molecules in cells, the stochastic nature of reactions, and the dynamic nature of macromolecular machines.
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Affiliation(s)
- Maxime Leroux
- Department of Biology, McGill University, Montreal, QC, Canada
| | - Nicolas Soubry
- Department of Biology, McGill University, Montreal, QC, Canada
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12
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Campion C, Charbon G, Thomsen TT, Nielsen PE, Løbner-Olesen A. Antisense inhibition of the Escherichia coli NrdAB aerobic ribonucleotide reductase is bactericidal due to induction of DNA strand breaks. J Antimicrob Chemother 2021; 76:2802-2814. [PMID: 34450639 PMCID: PMC8521395 DOI: 10.1093/jac/dkab305] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 07/16/2021] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Antisense peptide nucleic acids (PNAs) constitute an alternative to traditional antibiotics, by their ability to silence essential genes. OBJECTIVES To evaluate the antibacterial effects of antisense PNA-peptide conjugates that target the gene encoding the alpha subunit (NrdA) of the Escherichia coli ribonucleotide reductase (RNR). METHODS Bacterial susceptibility of a series of NrdA-targeting PNAs was studied by MIC determination and time-kill analysis. Western-blot analysis, gene complementation and synergy with hydroxyurea were employed to determine the efficiency of NrdA-PNA antisense treatment. The effect on chromosome replication was addressed by determining the DNA synthesis rate, by flow cytometry analysis, by quantitative PCR and by fluorescence microscopy. The use of DNA repair mutants provided insight into the bactericidal action of NrdA-PNA. RESULTS Treatment with NrdA-PNA specifically inhibited growth of E. coli, as well as NrdA protein translation at 4 μM. Also, the DNA synthesis rate was reduced, preventing completion of chromosome replication and resulting in formation of double-stranded DNA breaks and cell death. CONCLUSIONS These data present subunits of the NrdAB RNR as a target for future antisense microbial agents and provide insight into the bacterial physiological response to RNR-targeting antimicrobials.
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Affiliation(s)
- Christopher Campion
- Department of Cellular and Molecular Medicine, Faculty of Health Sciences, Center for Peptide-Based Antibiotics, The Panum Institute, University of Copenhagen, Blegdamsvej 3c, 2200 Copenhagen N, Denmark.,Department of Biology, Faculty of Science, Section for Functional Genomics, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen N, Denmark
| | - Godefroid Charbon
- Department of Biology, Faculty of Science, Section for Functional Genomics, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen N, Denmark
| | - Thomas T Thomsen
- Department of Biology, Faculty of Science, Section for Functional Genomics, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen N, Denmark.,Department of Clinical Microbiology, Rigshospitalet, Henrik Harpestreng Vej 4A, 2100 Copenhagen, Denmark
| | - Peter E Nielsen
- Department of Cellular and Molecular Medicine, Faculty of Health Sciences, Center for Peptide-Based Antibiotics, The Panum Institute, University of Copenhagen, Blegdamsvej 3c, 2200 Copenhagen N, Denmark
| | - Anders Løbner-Olesen
- Department of Biology, Faculty of Science, Section for Functional Genomics, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen N, Denmark
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13
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Bainbridge LJ, Teague R, Doherty AJ. Repriming DNA synthesis: an intrinsic restart pathway that maintains efficient genome replication. Nucleic Acids Res 2021; 49:4831-4847. [PMID: 33744934 PMCID: PMC8136793 DOI: 10.1093/nar/gkab176] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 03/01/2021] [Accepted: 03/05/2021] [Indexed: 12/25/2022] Open
Abstract
To bypass a diverse range of fork stalling impediments encountered during genome replication, cells possess a variety of DNA damage tolerance (DDT) mechanisms including translesion synthesis, template switching, and fork reversal. These pathways function to bypass obstacles and allow efficient DNA synthesis to be maintained. In addition, lagging strand obstacles can also be circumvented by downstream priming during Okazaki fragment generation, leaving gaps to be filled post-replication. Whether repriming occurs on the leading strand has been intensely debated over the past half-century. Early studies indicated that both DNA strands were synthesised discontinuously. Although later studies suggested that leading strand synthesis was continuous, leading to the preferred semi-discontinuous replication model. However, more recently it has been established that replicative primases can perform leading strand repriming in prokaryotes. An analogous fork restart mechanism has also been identified in most eukaryotes, which possess a specialist primase called PrimPol that conducts repriming downstream of stalling lesions and structures. PrimPol also plays a more general role in maintaining efficient fork progression. Here, we review and discuss the historical evidence and recent discoveries that substantiate repriming as an intrinsic replication restart pathway for maintaining efficient genome duplication across all domains of life.
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Affiliation(s)
- Lewis J Bainbridge
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, BN1 9RQ, UK
| | - Rebecca Teague
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, BN1 9RQ, UK
| | - Aidan J Doherty
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, BN1 9RQ, UK
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14
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Vaisman A, Łazowski K, Reijns MAM, Walsh E, McDonald JP, Moreno KC, Quiros DR, Schmidt M, Kranz H, Yang W, Makiela-Dzbenska K, Woodgate R. Novel Escherichia coli active site dnaE alleles with altered base and sugar selectivity. Mol Microbiol 2021; 116:909-925. [PMID: 34181784 PMCID: PMC8485763 DOI: 10.1111/mmi.14779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 06/25/2021] [Accepted: 06/26/2021] [Indexed: 11/26/2022]
Abstract
The Escherichia coli dnaE gene encodes the α‐catalytic subunit (pol IIIα) of DNA polymerase III, the cell’s main replicase. Like all high‐fidelity DNA polymerases, pol III possesses stringent base and sugar discrimination. The latter is mediated by a so‐called “steric gate” residue in the active site of the polymerase that physically clashes with the 2′‐OH of an incoming ribonucleotide. Our structural modeling data suggest that H760 is the steric gate residue in E.coli pol IIIα. To understand how H760 and the adjacent S759 residue help maintain genome stability, we generated DNA fragments in which the codons for H760 or S759 were systematically changed to the other nineteen naturally occurring amino acids and attempted to clone them into a plasmid expressing pol III core (α‐θ‐ε subunits). Of the possible 38 mutants, only nine were successfully sub‐cloned: three with substitutions at H760 and 6 with substitutions at S759. Three of the plasmid‐encoded alleles, S759C, S759N, and S759T, exhibited mild to moderate mutator activity and were moved onto the chromosome for further characterization. These studies revealed altered phenotypes regarding deoxyribonucleotide base selectivity and ribonucleotide discrimination. We believe that these are the first dnaE mutants with such phenotypes to be reported in the literature.
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Affiliation(s)
- Alexandra Vaisman
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Krystian Łazowski
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Martin A M Reijns
- MRC Human Genetics Unit, Institute of Genetics and Cancer, The University of Edinburgh, Western General Hospital, Edinburgh, UK
| | - Erin Walsh
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - John P McDonald
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Kristiniana C Moreno
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Dominic R Quiros
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Marlen Schmidt
- Gen-H Genetic Engineering Heidelberg GmbH, Heidelberg, Germany
| | - Harald Kranz
- Gen-H Genetic Engineering Heidelberg GmbH, Heidelberg, Germany
| | - Wei Yang
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Karolina Makiela-Dzbenska
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Roger Woodgate
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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15
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Yang Y, Wang T, Yu Q, Liu H, Xun L, Xia Y. The pathway of recombining short homologous ends in Escherichia coli revealed by the genetic study. Mol Microbiol 2021; 115:1309-1322. [PMID: 33372330 DOI: 10.1111/mmi.14677] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 12/17/2020] [Accepted: 12/23/2020] [Indexed: 11/30/2022]
Abstract
The recombination of short homologous ends in Escherichia coli has been known for 30 years, and it is often used for both site-directed mutagenesis and in vivo cloning. For cloning, a plasmid and target DNA fragments were converted into linear DNA fragments with short homologous ends, which are joined via recombination inside E. coli after transformation. Here this mechanism of joining homologous ends in E. coli was determined by a linearized plasmid with short homologous ends. Two 3'-5' exonucleases ExoIII and ExoX with nonprocessive activity digested linear dsDNA to generate 5' single-strand overhangs, which annealed with each other. The polymerase activity of DNA polymerase I (Pol I) was exclusively employed to fill in the gaps. The strand displacement activity and the 5'-3' exonuclease activity of Pol I were also required, likely to generate 5' phosphate termini for subsequent ligation. Ligase A (LigA) joined the nicks to finish the process. The model involving 5' single-stranded overhangs is different from established recombination pathways that all generate 3' single-stranded overhangs. This recombination is likely common in bacteria since the involved enzymes are ubiquitous.
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Affiliation(s)
- Yuqing Yang
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China.,Institute of Marine Science and Technology, Shandong University, Qingdao, People's Republic of China
| | - Tianqi Wang
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China
| | - Qiaoli Yu
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China
| | - Huaiwei Liu
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China
| | - Luying Xun
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China.,School of Molecular Biosciences, Washington State University, Pullman, WA, USA
| | - Yongzhen Xia
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, People's Republic of China
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16
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Pavlov YI, Zhuk AS, Stepchenkova EI. DNA Polymerases at the Eukaryotic Replication Fork Thirty Years after: Connection to Cancer. Cancers (Basel) 2020; 12:E3489. [PMID: 33255191 PMCID: PMC7760166 DOI: 10.3390/cancers12123489] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 11/13/2020] [Accepted: 11/13/2020] [Indexed: 12/13/2022] Open
Abstract
Recent studies on tumor genomes revealed that mutations in genes of replicative DNA polymerases cause a predisposition for cancer by increasing genome instability. The past 10 years have uncovered exciting details about the structure and function of replicative DNA polymerases and the replication fork organization. The principal idea of participation of different polymerases in specific transactions at the fork proposed by Morrison and coauthors 30 years ago and later named "division of labor," remains standing, with an amendment of the broader role of polymerase δ in the replication of both the lagging and leading DNA strands. However, cancer-associated mutations predominantly affect the catalytic subunit of polymerase ε that participates in leading strand DNA synthesis. We analyze how new findings in the DNA replication field help elucidate the polymerase variants' effects on cancer.
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Affiliation(s)
- Youri I. Pavlov
- Eppley Institute for Research in Cancer and Allied Diseases and Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Department of Genetics and Biotechnology, Saint-Petersburg State University, 199034 Saint Petersburg, Russia;
| | - Anna S. Zhuk
- International Laboratory of Computer Technologies, ITMO University, 197101 Saint Petersburg, Russia;
| | - Elena I. Stepchenkova
- Department of Genetics and Biotechnology, Saint-Petersburg State University, 199034 Saint Petersburg, Russia;
- Laboratory of Mutagenesis and Genetic Toxicology, Vavilov Institute of General Genetics, Saint-Petersburg Branch, Russian Academy of Sciences, 199034 Saint Petersburg, Russia
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17
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A Comprehensive View of Translesion Synthesis in Escherichia coli. Microbiol Mol Biol Rev 2020; 84:84/3/e00002-20. [PMID: 32554755 DOI: 10.1128/mmbr.00002-20] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The lesion bypass pathway, translesion synthesis (TLS), exists in essentially all organisms and is considered a pathway for postreplicative gap repair and, at the same time, for lesion tolerance. As with the saying "a trip is not over until you get back home," studying TLS only at the site of the lesion is not enough to understand the whole process of TLS. Recently, a genetic study uncovered that polymerase V (Pol V), a poorly expressed Escherichia coli TLS polymerase, is not only involved in the TLS step per se but also participates in the gap-filling reaction over several hundred nucleotides. The same study revealed that in contrast, Pol IV, another highly expressed TLS polymerase, essentially stays away from the gap-filling reaction. These observations imply fundamentally different ways these polymerases are recruited to DNA in cells. While access of Pol IV appears to be governed by mass action, efficient recruitment of Pol V involves a chaperone-like action of the RecA filament. We present a model of Pol V activation: the 3' tip of the RecA filament initially stabilizes Pol V to allow stable complex formation with a sliding β-clamp, followed by the capture of the terminal RecA monomer by Pol V, thus forming a functional Pol V complex. This activation process likely determines higher accessibility of Pol V than of Pol IV to normal DNA. Finally, we discuss the biological significance of TLS polymerases during gap-filling reactions: error-prone gap-filling synthesis may contribute as a driving force for genetic diversity, adaptive mutation, and evolution.
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18
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Ghodke PP, Guengerich FP. Impact of 1, N 6-ethenoadenosine, a damaged ribonucleotide in DNA, on translesion synthesis and repair. J Biol Chem 2020; 295:6092-6107. [PMID: 32213600 DOI: 10.1074/jbc.ra120.012829] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 03/23/2020] [Indexed: 01/02/2023] Open
Abstract
Incorporation of ribonucleotides into DNA can severely diminish genome integrity. However, how ribonucleotides instigate DNA damage is poorly understood. In DNA, they can promote replication stress and genomic instability and have been implicated in several diseases. We report here the impact of the ribonucleotide rATP and of its naturally occurring damaged analog 1,N 6-ethenoadenosine (1,N 6-ϵrA) on translesion synthesis (TLS), mediated by human DNA polymerase η (hpol η), and on RNase H2-mediated incision. Mass spectral analysis revealed that 1,N 6-ϵrA in DNA generates extensive frameshifts during TLS, which can lead to genomic instability. Moreover, steady-state kinetic analysis of the TLS process indicated that deoxypurines (i.e. dATP and dGTP) are inserted predominantly opposite 1,N 6-ϵrA. We also show that hpol η acts as a reverse transcriptase in the presence of damaged ribonucleotide 1,N 6-ϵrA but has poor RNA primer extension activities. Steady-state kinetic analysis of reverse transcription and RNA primer extension showed that hpol η favors the addition of dATP and dGTP opposite 1,N 6-ϵrA. We also found that RNase H2 recognizes 1,N 6-ϵrA but has limited incision activity across from this lesion, which can lead to the persistence of this detrimental DNA adduct. We conclude that the damaged and unrepaired ribonucleotide 1,N 6-ϵrA in DNA exhibits mutagenic potential and can also alter the reading frame in an mRNA transcript because 1,N 6-ϵrA is incompletely incised by RNase H2.
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Affiliation(s)
- Pratibha P Ghodke
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37323-0146
| | - F Peter Guengerich
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37323-0146.
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19
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Makiela-Dzbenska K, Maslowska KH, Kuban W, Gawel D, Jonczyk P, Schaaper RM, Fijalkowska IJ. Replication fidelity in E. coli: Differential leading and lagging strand effects for dnaE antimutator alleles. DNA Repair (Amst) 2019; 83:102643. [PMID: 31324532 DOI: 10.1016/j.dnarep.2019.102643] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Revised: 07/01/2019] [Accepted: 07/03/2019] [Indexed: 12/29/2022]
Abstract
DNA Pol III holoenzyme (HE) is the major DNA replicase of Escherichia coli. It is a highly accurate enzyme responsible for simultaneously replicating the leading- and lagging DNA strands. Interestingly, the fidelity of replication for the two DNA strands is unequal, with a higher accuracy for lagging-strand replication. We have previously proposed this higher lagging-strand fidelity results from the more dissociative character of the lagging-strand polymerase. In support of this hypothesis, an E. coli mutant carrying a catalytic DNA polymerase subunit (DnaE915) characterized by decreased processivity yielded an antimutator phenotype (higher fidelity). The present work was undertaken to gain deeper insight into the factors that influence the fidelity of chromosomal DNA replication in E. coli. We used three different dnaE alleles (dnaE915, dnaE911, and dnaE941) that had previously been isolated as antimutators. We confirmed that each of the three dnaE alleles produced significant antimutator effects, but in addition showed that these antimutator effects proved largest for the normally less accurate leading strand. Additionally, in the presence of error-prone DNA polymerases, each of the three dnaE antimutator strains turned into mutators. The combined observations are fully supportive of our model in which the dissociative character of the DNA polymerase is an important determinant of in vivo replication fidelity. In this model, increased dissociation from terminal mismatches (i.e., potential mutations) leads to removal of the mismatches (antimutator effect), but in the presence of error-prone (or translesion) DNA polymerases the abandoned terminal mismatches become targets for error-prone extension (mutator effect). We also propose that these dnaE alleles are promising tools for studying polymerase exchanges at the replication fork.
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Affiliation(s)
- Karolina Makiela-Dzbenska
- Laboratory of Mutagenesis and DNA Repair, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Katarzyna H Maslowska
- Laboratory of Mutagenesis and DNA Repair, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Wojciech Kuban
- Laboratory of Mutagenesis and DNA Repair, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Damian Gawel
- Laboratory of Mutagenesis and DNA Repair, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Piotr Jonczyk
- Laboratory of Mutagenesis and DNA Repair, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Roel M Schaaper
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
| | - Iwona J Fijalkowska
- Laboratory of Mutagenesis and DNA Repair, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland.
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20
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Su Y, Ghodke PP, Egli M, Li L, Wang Y, Guengerich FP. Human DNA polymerase η has reverse transcriptase activity in cellular environments. J Biol Chem 2019; 294:6073-6081. [PMID: 30842261 DOI: 10.1074/jbc.ra119.007925] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/04/2019] [Indexed: 12/24/2022] Open
Abstract
Classical DNA and RNA polymerase (pol) enzymes have defined roles with their respective substrates, but several pols have been found to have multiple functions. We reported previously that purified human DNA pol η (hpol η) can incorporate both deoxyribonucleoside triphosphates (dNTPs) and ribonucleoside triphosphates (rNTPs) and can use both DNA and RNA as substrates. X-ray crystal structures revealed that two pol η residues, Phe-18 and Tyr-92, behave as steric gates to influence sugar selectivity. However, the physiological relevance of these phenomena has not been established. Here, we show that purified hpol η adds rNTPs to DNA primers at physiological rNTP concentrations and in the presence of competing dNTPs. When two rATPs were inserted opposite a cyclobutane pyrimidine dimer, the substrate was less efficiently cleaved by human RNase H2. Human XP-V fibroblast extracts, devoid of hpol η, could not add rNTPs to a DNA primer, but the expression of transfected hpol η in the cells restored this ability. XP-V cell extracts did not add dNTPs to DNA primers hybridized to RNA, but could when hpol η was expressed in the cells. HEK293T cell extracts could add dNTPs to DNA primers hybridized to RNA, but lost this ability if hpol η was deleted. Interestingly, a similar phenomenon was not observed when other translesion synthesis (TLS) DNA polymerases-hpol ι, κ, or ζ-were individually deleted. These results suggest that hpol η is one of the major reverse transcriptases involved in physiological processes in human cells.
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Affiliation(s)
- Yan Su
- From the Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
| | - Pratibha P Ghodke
- From the Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
| | - Martin Egli
- From the Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
| | - Lin Li
- Department of Chemistry, University of California, Riverside, Riverside, California 92521
| | - Yinsheng Wang
- Department of Chemistry, University of California, Riverside, Riverside, California 92521
| | - F Peter Guengerich
- From the Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146.
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21
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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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22
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Solution to the 50-year-old Okazaki-fragment problem. Proc Natl Acad Sci U S A 2019; 116:3358-3360. [PMID: 30770440 DOI: 10.1073/pnas.1900372116] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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