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McMillan SD, Keck JL. Biochemical characterization of Escherichia coli DnaC variants that alter DnaB helicase loading onto DNA. J Biol Chem 2024; 300:107275. [PMID: 38588814 PMCID: PMC11087952 DOI: 10.1016/j.jbc.2024.107275] [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: 02/02/2024] [Revised: 03/29/2024] [Accepted: 04/01/2024] [Indexed: 04/10/2024] Open
Abstract
DNA replication in Escherichia coli starts with loading of the replicative helicase, DnaB, onto DNA. This reaction requires the DnaC loader protein, which forms a 6:6 complex with DnaB and opens a channel in the DnaB hexamer through which single-stranded DNA is thought to pass. During replication, replisomes frequently encounter DNA damage and nucleoprotein complexes that can lead to replication fork collapse. Such events require DnaB re-loading onto DNA to allow replication to continue. Replication restart proteins mediate this process by recruiting DnaB6/DnaC6 to abandoned DNA replication forks. Several dnaC mutations that bypass the requirement for replication restart proteins or that block replication restart have been identified in E. coli. To better understand how these DnaC variants function, we have purified and characterized the protein products of several such alleles. Unlike wild-type DnaC, three of the variants (DnaC 809, DnaC 809,820, and DnaC 811) can load DnaB onto replication forks bound by single-stranded DNA-binding protein. DnaC 809 can also load DnaB onto double-stranded DNA. These results suggest that structural changes in the variant DnaB6/DnaC6 complexes expand the range of DNA substrates that can be used for DnaB loading, obviating the need for the existing replication restart pathways. The protein product of dnaC1331, which phenocopies deletion of the priB replication restart gene, blocks loading through the major restart pathway in vitro. Overall, the results of our study highlight the utility of bacterial DnaC variants as tools for probing the regulatory mechanisms that govern replicative helicase loading.
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Affiliation(s)
- Sarah D McMillan
- Department of Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin, USA
| | - James L Keck
- Department of Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin, USA.
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2
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Direct visualization of translesion DNA synthesis polymerase IV at the replisome. Proc Natl Acad Sci U S A 2022; 119:e2208390119. [PMID: 36122225 PMCID: PMC9522359 DOI: 10.1073/pnas.2208390119] [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: 02/05/2023] Open
Abstract
In bacterial cells, DNA damage tolerance is manifested by the action of translesion DNA polymerases that can synthesize DNA across template lesions that typically block the replicative DNA polymerase III. It has been suggested that one of these translesion DNA synthesis DNA polymerases, DNA polymerase IV, can either act in concert with the replisome, switching places on the β sliding clamp with DNA polymerase III to bypass the template damage, or act subsequent to the replisome skipping over the template lesion in the gap in nascent DNA left behind as the replisome continues downstream. Evidence exists in support of both mechanisms. Using single-molecule analyses, we show that DNA polymerase IV associates with the replisome in a concentration-dependent manner and remains associated over long stretches of replication fork progression under unstressed conditions. This association slows the replisome, requires DNA polymerase IV binding to the β clamp but not its catalytic activity, and is reinforced by the presence of the γ subunit of the β clamp-loading DnaX complex in the DNA polymerase III holoenzyme. Thus, DNA damage is not required for association of DNA polymerase IV with the replisome. We suggest that under stress conditions such as induction of the SOS response, the association of DNA polymerase IV with the replisome provides both a surveillance/bypass mechanism and a means to slow replication fork progression, thereby reducing the frequency of collisions with template damage and the overall mutagenic potential.
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3
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Puri N, Fernandez AJ, O'Shea Murray VL, McMillan S, Keck JL, Berger JM. The molecular coupling between substrate recognition and ATP turnover in a AAA+ hexameric helicase loader. eLife 2021; 10:64232. [PMID: 34036936 PMCID: PMC8213410 DOI: 10.7554/elife.64232] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 05/25/2021] [Indexed: 11/16/2022] Open
Abstract
In many bacteria and eukaryotes, replication fork establishment requires the controlled loading of hexameric, ring-shaped helicases around DNA by AAA+(ATPases Associated with various cellular Activities) ATPases. How loading factors use ATP to control helicase deposition is poorly understood. Here, we dissect how specific ATPase elements of Escherichia coli DnaC, an archetypal loader for the bacterial DnaB helicase, play distinct roles in helicase loading and the activation of DNA unwinding. We have identified a new element, the arginine-coupler, which regulates the switch-like behavior of DnaC to prevent futile ATPase cycling and maintains loader responsiveness to replication restart systems. Our data help explain how the ATPase cycle of a AAA+-family helicase loader is channeled into productive action on its target; comparative studies indicate that elements analogous to the Arg-coupler are present in related, switch-like AAA+ proteins that control replicative helicase loading in eukaryotes, as well as in polymerase clamp loading and certain classes of DNA transposases.
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Affiliation(s)
- Neha Puri
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States
| | - Amy J Fernandez
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States
| | - Valerie L O'Shea Murray
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States.,Saul Ewing Arnstein & Lehr, LLP, Centre Square West, Philadelphia, United States
| | - Sarah McMillan
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, United States
| | - James L Keck
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, United States
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States
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Bianco PR. DNA Helicase-SSB Interactions Critical to the Regression and Restart of Stalled DNA Replication forks in Escherichia coli. Genes (Basel) 2020; 11:E471. [PMID: 32357475 PMCID: PMC7290993 DOI: 10.3390/genes11050471] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 04/21/2020] [Accepted: 04/23/2020] [Indexed: 01/25/2023] Open
Abstract
In Escherichia coli, DNA replication forks stall on average once per cell cycle. When this occurs, replisome components disengage from the DNA, exposing an intact, or nearly intact fork. Consequently, the fork structure must be regressed away from the initial impediment so that repair can occur. Regression is catalyzed by the powerful, monomeric DNA helicase, RecG. During this reaction, the enzyme couples unwinding of fork arms to rewinding of duplex DNA resulting in the formation of a Holliday junction. RecG works against large opposing forces enabling it to clear the fork of bound proteins. Following subsequent processing of the extruded junction, the PriA helicase mediates reloading of the replicative helicase DnaB leading to the resumption of DNA replication. The single-strand binding protein (SSB) plays a key role in mediating PriA and RecG functions at forks. It binds to each enzyme via linker/OB-fold interactions and controls helicase-fork loading sites in a substrate-dependent manner that involves helicase remodeling. Finally, it is displaced by RecG during fork regression. The intimate and dynamic SSB-helicase interactions play key roles in ensuring fork regression and DNA replication restart.
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Affiliation(s)
- Piero R Bianco
- Center for Single Molecule Biophysics, University at Buffalo, SUNY, Buffalo, NY 14221, USA
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5
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Killelea T, Hawkins M, Howard JL, McGlynn P, Bolt EL. DNA replication roadblocks caused by Cascade interference complexes are alleviated by RecG DNA repair helicase. RNA Biol 2018; 16:543-548. [PMID: 30096986 PMCID: PMC6546356 DOI: 10.1080/15476286.2018.1496773] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Cascade complexes underpin E. coli CRISPR-Cas immunity systems by stimulating 'adaptation' reactions that update immunity and by initiating 'interference' reactions that destroy invader DNA. Recognition of invader DNA in Cascade catalysed R-loops provokes DNA capture and its subsequent integration into CRISPR loci by Cas1 and Cas2. DNA capture processes are unclear but may involve RecG helicase, which stimulates adaptation during its role responding to genome instability. We show that Cascade is a potential source of genome instability because it blocks DNA replication and that RecG helicase alleviates this by dissociating Cascade. This highlights how integrating in vitro CRISPR-Cas interference and adaptation reactions with DNA replication and repair reactions will help to determine precise mechanisms underpinning prokaryotic adaptive immunity.
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Affiliation(s)
- Tom Killelea
- a School of Life Sciences, Queen's Medical Centre , University of Nottingham , Nottingham , UK
| | | | | | - Peter McGlynn
- b Department of Biology , University of York , York , UK
| | - Edward L Bolt
- a School of Life Sciences, Queen's Medical Centre , University of Nottingham , Nottingham , UK
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6
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Abstract
It has been assumed that DNA synthesis by the leading- and lagging-strand polymerases in the replisome must be coordinated to avoid the formation of significant gaps in the nascent strands. Using real-time single-molecule analysis, we establish that leading- and lagging-strand DNA polymerases function independently within a single replisome. Although average rates of DNA synthesis on leading and lagging strands are similar, individual trajectories of both DNA polymerases display stochastically switchable rates of synthesis interspersed with distinct pauses. DNA unwinding by the replicative helicase may continue during such pauses, but a self-governing mechanism, where helicase speed is reduced by ∼80%, permits recoupling of polymerase to helicase. These features imply a more dynamic, kinetically discontinuous replication process, wherein contacts within the replisome are continually broken and reformed. We conclude that the stochastic behavior of replisome components ensures complete DNA duplication without requiring coordination of leading- and lagging-strand synthesis. PAPERCLIP.
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7
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Abstract
In bacteria, replication forks assembled at a replication origin travel to the terminus, often a few megabases away. They may encounter obstacles that trigger replisome disassembly, rendering replication restart from abandoned forks crucial for cell viability. During the past 25 years, the genes that encode replication restart proteins have been identified and genetically characterized. In parallel, the enzymes were purified and analyzed in vitro, where they can catalyze replication initiation in a sequence-independent manner from fork-like DNA structures. This work also revealed a close link between replication and homologous recombination, as replication restart from recombination intermediates is an essential step of DNA double-strand break repair in bacteria and, conversely, arrested replication forks can be acted upon by recombination proteins and converted into various recombination substrates. In this review, we summarize this intense period of research that led to the characterization of the ubiquitous replication restart protein PriA and its partners, to the definition of several replication restart pathways in vivo, and to the description of tight links between replication and homologous recombination, responsible for the importance of replication restart in the maintenance of genome stability.
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8
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Abstract
Recombination-dependent DNA replication, often called break-induced replication (BIR), was initially invoked to explain recombination events in bacteriophage but it has recently been recognized as a fundamentally important mechanism to repair double-strand chromosome breaks in eukaryotes. This mechanism appears to be critically important in the restarting of stalled and broken replication forks and in maintaining the integrity of eroded telomeres. Although BIR helps preserve genome integrity during replication, it also promotes genome instability by the production of loss of heterozygosity and the formation of nonreciprocal translocations, as well as in the generation of complex chromosomal rearrangements.
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Affiliation(s)
- Ranjith P Anand
- Rosenstiel Basic Medical Sciences Research Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02254-9110
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9
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López-Madrigal S, Latorre A, Porcar M, Moya A, Gil R. Mealybugs nested endosymbiosis: going into the 'matryoshka' system in Planococcus citri in depth. BMC Microbiol 2013; 13:74. [PMID: 23548081 PMCID: PMC3620526 DOI: 10.1186/1471-2180-13-74] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Accepted: 03/25/2013] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND In all branches of life there are plenty of symbiotic associations. Insects are particularly well suited to establishing intracellular symbiosis with bacteria, providing them with metabolic capabilities they lack. Essential primary endosymbionts can coexist with facultative secondary symbionts which can, eventually, establish metabolic complementation with the primary endosymbiont, becoming a co-primary. Usually, both endosymbionts maintain their cellular identity. An exception is the endosymbiosis found in mealybugs of the subfamily Pseudoccinae, such as Planococcus citri, with Moranella endobia located inside Tremblaya princeps. RESULTS We report the genome sequencing of M. endobia str. PCVAL and the comparative genomic analyses of the genomes of strains PCVAL and PCIT of both consortium partners. A comprehensive analysis of their functional capabilities and interactions reveals their functional coupling, with many cases of metabolic and informational complementation. Using comparative genomics, we confirm that both genomes have undergone a reductive evolution, although with some unusual genomic features as a consequence of coevolving in an exceptional compartmentalized organization. CONCLUSIONS M. endobia seems to be responsible for the biosynthesis of most cellular components and energy provision, and controls most informational processes for the consortium, while T. princeps appears to be a mere factory for amino acid synthesis, and translating proteins, using the precursors provided by M. endobia. In this scenario, we propose that both entities should be considered part of a composite organism whose compartmentalized scheme (somehow) resembles a eukaryotic cell.
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Affiliation(s)
- Sergio López-Madrigal
- Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Apartado Postal 22085, València, 46071, Spain
| | - Amparo Latorre
- Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Apartado Postal 22085, València, 46071, Spain
- Área de Genómica y Salud, Centro Superior de Investigación en Salud Pública (CSISP), Avenida de Cataluña 21, Valencia, 46020, Spain
| | - Manuel Porcar
- Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Apartado Postal 22085, València, 46071, Spain
- Fundació General de la Universitat de València, Apartado Postal 22085, València, 46071, Spain
| | - Andrés Moya
- Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Apartado Postal 22085, València, 46071, Spain
- Área de Genómica y Salud, Centro Superior de Investigación en Salud Pública (CSISP), Avenida de Cataluña 21, Valencia, 46020, Spain
| | - Rosario Gil
- Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Apartado Postal 22085, València, 46071, Spain
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10
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Marceau AH, Bahng S, Massoni SC, George NP, Sandler SJ, Marians KJ, Keck JL. Structure of the SSB-DNA polymerase III interface and its role in DNA replication. EMBO J 2011; 30:4236-47. [PMID: 21857649 PMCID: PMC3199393 DOI: 10.1038/emboj.2011.305] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2011] [Accepted: 07/29/2011] [Indexed: 11/09/2022] Open
Abstract
Interactions between single-stranded DNA-binding proteins (SSBs) and the DNA replication machinery are found in all organisms, but the roles of these contacts remain poorly defined. In Escherichia coli, SSB's association with the χ subunit of the DNA polymerase III holoenzyme has been proposed to confer stability to the replisome and to aid delivery of primers to the lagging-strand DNA polymerase. Here, the SSB-binding site on χ is identified crystallographically and biochemical and cellular studies delineate the consequences of destabilizing the χ/SSB interface. An essential role for the χ/SSB interaction in lagging-strand primer utilization is not supported. However, sequence changes in χ that block complex formation with SSB lead to salt-dependent uncoupling of leading- and lagging-strand DNA synthesis and to a surprising obstruction of the leading-strand DNA polymerase in vitro, pointing to roles for the χ/SSB complex in replisome establishment and maintenance. Destabilization of the χ/SSB complex in vivo produces cells with temperature-dependent cell cycle defects that appear to arise from replisome instability.
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Affiliation(s)
- Aimee H Marceau
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706-1532, USA
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11
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Gabbai CB, Marians KJ. Recruitment to stalled replication forks of the PriA DNA helicase and replisome-loading activities is essential for survival. DNA Repair (Amst) 2010; 9:202-9. [PMID: 20097140 DOI: 10.1016/j.dnarep.2009.12.009] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
PriA, a 3'-->5' superfamily 2 DNA helicase, acts to remodel stalled replication forks and as a specificity factor for origin-independent assembly of a new replisome at the stalled fork. The ability of PriA to initiate replication at stalled forked structures ensures complete genome replication and helps to protect the cell from illegitimate recombination events. This review focuses on the activities of PriA and its role in replication fork assembly and maintaining genomic integrity.
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Affiliation(s)
- Carolina B Gabbai
- Molecular Biology Program, Weill-Cornell Graduate School of Medical Sciences, New York, NY, USA.
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12
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Wu L, Hickson ID. DNA helicases required for homologous recombination and repair of damaged replication forks. Annu Rev Genet 2007; 40:279-306. [PMID: 16856806 DOI: 10.1146/annurev.genet.40.110405.090636] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
DNA helicases are found in all kingdoms of life and function in all DNA metabolic processes where the two strands of duplex DNA require to be separated. Here, we review recent developments in our understanding of the roles that helicases play in the intimately linked processes of replication fork repair and homologous recombination, and highlight how the cell has evolved many distinct, and sometimes antagonistic, uses for these enzymes.
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Affiliation(s)
- Leonard Wu
- Cancer Research UK, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, OX3 9DS, United Kingdom
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13
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Boonsombat R, Yeh SP, Milne A, Sandler SJ. A novel dnaC mutation that suppresses priB rep mutant phenotypes in Escherichia coli K-12. Mol Microbiol 2006; 60:973-83. [PMID: 16677308 DOI: 10.1111/j.1365-2958.2006.05147.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The loading of a replisome in prokaryotic and eukaryotic cells at an origin of DNA replication and during replication restart is a highly ordered and regulated process. During replication restart in Escherichia coli, the PriA, PriB, PriC, DnaT and Rep proteins form multiple pathways that bind to repaired replication forks. These complexes are then recognized by DnaC as sites to load DnaB, the replicative helicase. Several dnaC mutations have been isolated that suppress phenotypes of some replication restart mutants. A new dnaC mutation (dnaC824) is reported here that efficiently suppresses priB rep mutant phenotypes. Furthermore, it is shown that dnaC824 will suppress phenotypes of priB priA300, rep priA300 and priB priC strains. Unlike other dnaC suppressors, it can only weakly suppress the absence of priA. Others have reported a different type of dnaC mutation, dnaC1331, is able to mimic priB mutant phenotypes. This is supported herein by showing that like dnaC1331, a priB mutation is synthetically lethal with a dam mutation and this can be rescued by a mutH mutation. Furthermore, priB dam lethality can also be suppressed by dnaC824. Like a priB mutation, a dnaC1331 mutation causes a priA2::kan-like phenotype when combined with priA300. Lastly, we show that dnaC824 is dominant to wild type and that dnaC1331 is recessive to wild type. Several models are discussed for the action of these mutant dnaC proteins in replication restart.
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Affiliation(s)
- Ruethairat Boonsombat
- Department of Microbiology, Morrill Science Center IV N203, University of Massachusetts at Amherst, Amherst, MA 01003, USA
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14
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Heller RC, Marians KJ. Replication fork reactivation downstream of a blocked nascent leading strand. Nature 2006; 439:557-62. [PMID: 16452972 DOI: 10.1038/nature04329] [Citation(s) in RCA: 253] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 10/17/2005] [Indexed: 11/08/2022]
Abstract
Unrepaired lesions in the DNA template pose a threat to accurate replication. Several pathways exist in Escherichia coli to reactivate a blocked replication fork. The process of recombination-dependent restart of broken forks is well understood, but the consequence of replication through strand-specific lesions is less well known. Here we show that replication can be restarted and leading-strand synthesis re-initiated downstream of an unrepaired block to leading-strand progression, even when the 3'-OH of the nascent leading strand is unavailable. We demonstrate that the loading by a replication restart system of a single hexamer of the replication fork helicase, DnaB, on the lagging-strand template is sufficient to coordinate priming by the DnaG primase of both the leading and lagging strands. These observations provide a mechanism for damage bypass during fork reactivation, demonstrate how daughter-strand gaps are generated opposite leading-strand lesions during the replication of ultraviolet-light-irradiated DNA, and help to explain the remarkable speed at which even a heavily damaged DNA template is replicated.
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Affiliation(s)
- Ryan C Heller
- Molecular Biology Program, Weill Graduate School of Medical Sciences of Cornell University, New York, New York 10021, USA
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15
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North SH, Nakai H. Host factors that promote transpososome disassembly and the PriA-PriC pathway for restart primosome assembly. Mol Microbiol 2005; 56:1601-16. [PMID: 15916609 DOI: 10.1111/j.1365-2958.2005.04639.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Initiation of bacteriophage Mu DNA replication by transposition requires the disassembly of the transpososome that catalyses strand exchange and the assembly of a replisome promoted by PriA, PriB, PriC and DnaT proteins, which function in the host to restart stalled replication forks. Once the molecular chaperone ClpX weakens the very tight binding of the transpososome to the Mu ends, host disassembly factors (MRFalpha-DF) promote the dissociation of the transpososome from the DNA template and the assembly of a new nucleoprotein complex. Prereplisome factors (MRFalpha-PR) further alter the complex, allowing PriA binding and loading of major replicative helicase DnaB onto the template promoted by the restart proteins. MRFalpha-PR is essential for DnaB loading by restart proteins even on the deproteinized Mu fork whereas MRFalpha-DF is not required on the deproteinized template. When the transition from transpososome to replisome was reconstituted using MRFalpha-DF and MRFalpha-PR, initiation of Mu DNA replication was strictly dependent upon added PriC and PriA helicase. In contrast, initiation on the deproteinized template was predominantly dependent upon PriB and did not require PriA's helicase activity. The results indicate that transition mechanisms beginning with the transpososome disassembly can determine the pathway of replisome assembly by restart proteins.
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Affiliation(s)
- Stella H North
- Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, Room 331 Basic Science Bldg., 3900 Reservoir Road NW, Washington, DC 20057-1455, USA
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Sperandio B, Polard P, Ehrlich DS, Renault P, Guédon E. Sulfur amino acid metabolism and its control in Lactococcus lactis IL1403. J Bacteriol 2005; 187:3762-78. [PMID: 15901700 PMCID: PMC1112055 DOI: 10.1128/jb.187.11.3762-3778.2005] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cysteine and methionine availability influences many processes in the cell. In bacteria, transcription of the specific genes involved in the synthesis of these two amino acids is usually regulated by different mechanisms or regulators. Pathways for the synthesis of cysteine and methionine and their interconversion were experimentally determined for Lactococcus lactis, a lactic acid bacterium commonly found in food. A new gene, yhcE, was shown to be involved in methionine recycling to cysteine. Surprisingly, 18 genes, representing almost all genes of these pathways, are under the control of a LysR-type activator, FhuR, also named CmbR. DNA microarray experiments showed that FhuR targets are restricted to this set of 18 genes clustered in seven transcriptional units, while cysteine starvation modifies the transcription level of several other genes potentially involved in oxidoreduction processes. Purified FhuR binds a 13-bp box centered 46 to 53 bp upstream of the transcriptional starts from the seven regulated promoters, while a second box with the same consensus is present upstream of the first binding box, separated by 8 to 10 bp. O-Acetyl serine increases FhuR binding affinity to its binding boxes. The overall view of sulfur amino acid metabolism and its regulation in L. lactis indicates that CysE could be a master enzyme controlling the activity of FhuR by providing its effector, while other controls at the enzymatic level appear to be necessary to compensate the absence of differential regulation of the genes involved in the interconversion of methionine and cysteine and other biosynthesis genes.
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Affiliation(s)
- Brice Sperandio
- Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas cedex, France
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17
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Bruand C, Velten M, McGovern S, Marsin S, Sérèna C, Ehrlich SD, Polard P. Functional interplay between the Bacillus subtilis DnaD and DnaB proteins essential for initiation and re-initiation of DNA replication. Mol Microbiol 2005; 55:1138-50. [PMID: 15686560 DOI: 10.1111/j.1365-2958.2004.04451.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Initiation and re-initiation of chromosomal DNA replication in bacteria rely on divergent multiprotein assemblies, which direct the functional delivery of the replicative helicase on single-stranded DNA (ssDNA) at specific sites. These two processes are triggered either at the single chromosomal origin oriC or at arrested forks by the conserved DnaA and PriA proteins respectively. In Bacillus subtilis, these two pathways further require the three essential proteins DnaB, DnaD and DnaI, restrictively encoded in Gram positive bacteria of low GC content. We have recently shown that DnaI and DnaB act as a pair of loaders of the DnaC replicative helicase. The role of DnaD appeared more enigmatic. It was previously shown to interact with DnaA and to display weak ssDNA binding activity. Here, we report that purified DnaD can interact physically with PriA and with DnaB. We show that the lethality of the temperature-sensitive dnaD23 mutant can be suppressed by different DnaB point mutants, which were found to be identical to the suppressors of priA null mutants. The DnaD23 protein displays lower ssDNA binding activity than DnaD. Conversely, the DnaB75 protein, the main dnaD23 suppressor, has gained affinity for ssDNA. Finally, we observed that this interplay between DnaD and DnaB is crucial for their concerted interaction with SSB-coated ssDNA, which is the expected substrate for the loading of the replicative helicase in vivo. Altogether, these results highlight the need for both DnaD and DnaB to interact individually and together with ssDNA during the early stages of initiation and re-initiation of chromosomal DNA replication. They also point at a main structural role of DnaD in the multiprotein assemblies built during these two essential processes.
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Affiliation(s)
- Claude Bruand
- Laboratoire de Génétique Microbienne, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas, France
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Heller RC, Marians KJ. The Disposition of Nascent Strands at Stalled Replication Forks Dictates the Pathway of Replisome Loading during Restart. Mol Cell 2005; 17:733-43. [PMID: 15749022 DOI: 10.1016/j.molcel.2005.01.019] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Revised: 12/31/2004] [Accepted: 01/25/2005] [Indexed: 11/26/2022]
Abstract
Rescue of arrested and collapsed replication forks is essential for maintenance of genomic integrity. One system for origin of replication-independent loading of the DnaB replicative helicase and subsequent replisome reassembly requires the structure-specific recognition factor PriA and the assembly factors PriB and DnaT. Here, we provide biochemical evidence for an alternate system for DnaB loading that requires only PriC. Furthermore, the choice of which system is utilized during restart is dictated by the nature of the structure of the stalled replication fork. PriA-dependent reactions are most robust on fork structures with no gaps in the leading strand, such as is found at the junction of a D loop, while the PriC-dependent system preferentially utilizes fork structures with large gaps in the leading strand. These observations suggest that the type of initial damage on the DNA template and how the inactivated fork is processed ultimately influence the choice of enzymatic restart pathway.
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Affiliation(s)
- Ryan C Heller
- Program in Molecular Biology, Weill Graduate School of Medical Sciences, Cornell University, New York, New York 10021, USA
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19
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Sandler SJ. Requirements for replication restart proteins during constitutive stable DNA replication in Escherichia coli K-12. Genetics 2005; 169:1799-806. [PMID: 15716497 PMCID: PMC1449598 DOI: 10.1534/genetics.104.036962] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Constitutive stable DNA replication (cSDR) is a mechanism for replisome loading in Escherichia coli K-12. This occurs in a dnaA-independent fashion in an rnhA mutant. cSDR is dependent on recA, priA, and transcription. In this report, it is shown that dnaA rnhA mutants using cSDR for initiation of their DNA replication additionally require priB, but not priC, for viability. Two subtle priA missense mutations either eliminated the ability to grow using cSDR (priA301 C479Y) or resulted in very small colonies (priA300 K230R). DnaC809, a priA suppressor, failed to allow priA or priB mutants to grow using cSDR to initiate DNA replication. Furthermore, unlike dnaC(+) strains, dnaC809 strains require priC for cSDR. DnaC809,820, a priC-independent suppressor of priA2::kan phenotypes, allowed priA and priC (but not priB) mutants to grow using cSDR to initiate DNA replication. It is also shown that rep and rnhA mutations are synthetically lethal. DnaC809 and dnaC809,820 mutations suppress this lethality. Rep is further shown to be required for cSDR in a dnaC809 strain. A model whereby these different sets of replication restart proteins interact preferentially with substrates associated with either RecA or SSB during replication restart and cSDR, respectively, is proposed.
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Affiliation(s)
- Steven J Sandler
- Department of Microbiology, University of Massachusetts, Amherst, 01003, USA.
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20
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Rokop ME, Auchtung JM, Grossman AD. Control of DNA replication initiation by recruitment of an essential initiation protein to the membrane of Bacillus subtilis. Mol Microbiol 2005; 52:1757-67. [PMID: 15186423 DOI: 10.1111/j.1365-2958.2004.04091.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Bacillus subtilis proteins DnaD and DnaB are essential for replication initiation and are conserved in low G+C content Gram-positive bacteria. Previous work indicated that DnaD and DnaB are involved in helicase loading during the process of restarting stalled replication forks. We have investigated the roles of DnaD and DnaB in replication initiation at oriC in vivo. Using chromatin immunoprecipitation (ChIP), we found that DnaD and DnaB functions are needed to load the replicative helicase at oriC. To investigate further the functions of DnaD and DnaB in replication initiation, we isolated and characterized suppressors of the temperature sensitivity of dnaD and dnaB mutant cells. In both cases, we isolated the identical missense mutation in dnaB, dnaBS371P. Using yeast two-hybrid analysis, we found that dnaBS371P uncovers a previously undetected physical interaction between DnaD and DnaB. We also found that DnaBS371P constitutively recruits DnaD to the membrane fraction of cells, where DnaB and oriC are enriched. Phenotypes of cells expressing DnaBS371P are consistent with aberrant replication control. We hypothesize that B. subtilis regulates replication initiation by regulating a physical interaction between two proteins essential for helicase loading at chromosomal origins.
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Affiliation(s)
- Megan E Rokop
- Department of Biology, Building 68-530, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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21
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Grompone G, Sanchez N, Dusko Ehrlich S, Michel B. Requirement for RecFOR-mediated recombination in priA mutant. Mol Microbiol 2004; 52:551-62. [PMID: 15066040 DOI: 10.1111/j.1365-2958.2004.03997.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Restart of arrested replication forks is an important process and PriA, the main Escherichia coli replication restart protein, is essential for viability under any condition that increases the frequency of fork arrest. In priA mutant, replication forks are arrested by spontaneously occurring roadblocks and blocked replication forks persist as a result of the defect in replication restart. In the present work, we analysed how recombination proteins contribute to the viability of the priA mutant. RecFOR-mediated homologous recombination occurs in a large fraction of priA mutant cells, indicating a frequent formation of DNA single strand gaps and their recombinational repair. This high level of homologous recombination renders the proteins that resolve Holliday junctions recombination intermediates essential for viability. When homologous recombination is blocked at early steps by recFOR or recA inactivation, exonuclease V-mediated DNA degradation is required for full viability of priA mutants, indicating that unrepaired gaps are broken and that DNA degradation of the broken DNA allows the formation of viable cells. Models for the formation of single strand DNA gaps consequently to a replication restart defect and for gap processing are proposed.
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Affiliation(s)
- Gianfranco Grompone
- Génétique Microbienne, Institut National de la Recherche Agronomique, Domaine de Vilvert 78350 Jouy en Josas, France
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22
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Grompone G, Bidnenko V, Ehrlich SD, Michel B. PriA is essential for viability of the Escherichia coli topoisomerase IV parE10(Ts) mutant. J Bacteriol 2004; 186:1197-9. [PMID: 14762016 PMCID: PMC344234 DOI: 10.1128/jb.186.4.1197-1199.2004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The parE10(Ts) mutation, which renders Escherichia coli thermosensitive for growth by inactivation of the essential E. coli topoisomerase topo IV, is lethal at all temperatures when PriA, the main replication restart protein, is absent. This lethality is suppressed by the activation of a PriA-independent replication restart pathway (dnaC809 mutation). This result suggests that topo IV acts prior to full-chromosome replication completion.
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Affiliation(s)
- Gianfranco Grompone
- Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas, France
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23
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Abstract
Gyrase is an essential topoisomerase in bacteria that introduces negative supercoils in DNA and relaxes the positive supercoils that form downstream of proteins tracking on DNA, such as DNA or RNA polymerases. Two gyrase mutants that suffer partial loss of function were used here to study the need for replication restart in conditions in which gyrase activity is affected. We show that the preprimosomal protein PriA is essential for the viability of these gyrB mutants. The helicase function of PriA is not essential. The lethality of the gyrB priA double mutants is suppressed by a dnaC809 mutation, indicating a requirement for primosome assembly in gyrB strains. The lethality of gyrB priA combination of mutations is independent of the level of DNA supercoiling, as gyrB and priA were also co-lethal in the presence of a DeltatopA mutation. Inactivation of homologous recombination did not affect the viability of gyrB mutants, indicating that replication restart does not require the formation of a recombination intermediate. We propose that the replisome is disassembled from replication forks when replication progression is blocked by the accumulation of positive supercoils in gyrase mutants, and that replication restarts via PriA-dependent primosome assembly, directly on the in-activated replication forks, without the formation of a recombination intermediate.
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Affiliation(s)
- Gianfranco Grompone
- Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas, France
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24
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Velten M, McGovern S, Marsin S, Ehrlich SD, Noirot P, Polard P. A two-protein strategy for the functional loading of a cellular replicative DNA helicase. Mol Cell 2003; 11:1009-20. [PMID: 12718886 DOI: 10.1016/s1097-2765(03)00130-8] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The delivery of a ring-shaped hexameric helicase onto DNA is a fundamental step of DNA replication, conserved in all cellular organisms. We report the biochemical characterization of the bacterial hexameric replicative helicase DnaC of Bacillus subtilis with that of the two replication initiation proteins DnaI and DnaB. We show that DnaI and DnaB interact physically and functionally with the DnaC helicase and mediate its functional delivery onto DNA. Thus, DnaB and DnaI form a pair of helicase loaders, revealing a two-protein strategy for the loading of a replicative helicase. We also present evidence that the DnaC helicase loading mechanism appears to be of the ring-assembly type, proceeding through the recruitment of DnaC monomers and their hexamerization around single-stranded DNA by the coordinated action of DnaI and DnaB.
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Affiliation(s)
- Marion Velten
- Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, Domaine de Vilvert, 78352 Jouy en Josas, France
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25
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Moore T, McGlynn P, Ngo HP, Sharples GJ, Lloyd RG. The RdgC protein of Escherichia coli binds DNA and counters a toxic effect of RecFOR in strains lacking the replication restart protein PriA. EMBO J 2003; 22:735-45. [PMID: 12554673 PMCID: PMC140733 DOI: 10.1093/emboj/cdg048] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
PriA protein provides a means to load the DnaB replicative helicase at DNA replication fork and D loop structures, and is therefore a key factor in the rescue of stalled or broken forks and subsequent replication restart. We show that the nucleoid-associated RdgC protein binds non-specifically to single-stranded (ss) DNA and double-stranded DNA. It is also essential for growth of a strain lacking PriA, indicating that it might affect replication fork progression or fork rescue. dnaC suppressors of priA overcome this inviability, especially when RecF, RecO or RecR is inactivated, indicating that RdgC avoids or counters a toxic effect of these proteins. Mutations modifying ssDNA-binding (SSB) protein also negate this toxic effect, suggesting that the toxicity reflects inappropriate loading of RecA on SSB-coated ssDNA, leading to excessive or untimely RecA activity. We suggest that binding of RdgC to DNA limits RecA loading, avoiding problems at replication forks that would otherwise require PriA to promote replication restart. Mutations in RNA polymerase also reduce the toxic effect of RecFOR, providing a further link between DNA replication, transcription and repair.
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Affiliation(s)
| | | | | | - Gary J. Sharples
- Institute of Genetics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK
Present address: Centre for Infectious Diseases, University of Durham, Wolfson Research Institute, Queen’s Campus, Stockton-on-Tees TS17 6BH, UK Corresponding author e-mail:
| | - Robert G. Lloyd
- Institute of Genetics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK
Present address: Centre for Infectious Diseases, University of Durham, Wolfson Research Institute, Queen’s Campus, Stockton-on-Tees TS17 6BH, UK Corresponding author e-mail:
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26
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Flores MJ, Ehrlich SD, Michel B. Primosome assembly requirement for replication restart in the Escherichia coli holDG10 replication mutant. Mol Microbiol 2002; 44:783-92. [PMID: 11994158 DOI: 10.1046/j.1365-2958.2002.02913.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In this report, we study the role of pre-primosome proteins in a strain in which the frequency of replication arrest is increased because of a mutation in a replication protein. The holDG10 mutant was used, in which replication restart involves replication fork reversal. As expected, PriA primosome assembly function is essential for growth of the holDG10 mutant. The priA300 mutation, which inactivates only the helicase function of PriA in vitro, and priB inactivation strongly impair viability. In contrast, priC inactivation has no effect. Therefore, PriB is more important than PriC for PriA-dependent replication fork restart in vivo. The gain of function mutation dnaC809 restores the viability of holDG10 priA and holDG10 priB mutants only to some extent. The dnaC809 820 double mutation restores full viability to the holDG10 mutant lacking either PriA or PriB. Similarly to the holDG10 single mutant, the holDG10 priA dnaC809 820 strain is depend-ent on RecBC for viability, indicating that facilitating primosome assembly using the dnaC809 820 mutation does not allow bypass of replication fork reversal.
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Affiliation(s)
- Maria Jose Flores
- Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, Jouy en Josas, France
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27
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Rangarajan S, Woodgate R, Goodman MF. Replication restart in UV-irradiated Escherichia coli involving pols II, III, V, PriA, RecA and RecFOR proteins. Mol Microbiol 2002; 43:617-28. [PMID: 11929519 DOI: 10.1046/j.1365-2958.2002.02747.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Escherichia coli, UV-irradiated cells resume DNA synthesis after a transient inhibition by a process called replication restart. To elucidate the role of several key proteins involved in this process, we have analysed the time dependence of replication restart in strains carrying a combination of mutations in lexA, recA, polB (pol II), umuDC (pol V), priA, dnaC, recF, recO or recR. We find that both pol II and the origin-independent primosome-assembling function of PriA are essential for the immediate recovery of DNA synthesis after UV irradiation. In their absence, translesion replication or 'replication readthrough' occurs approximately 50 min after UV and is pol V-dependent. In a wild-type, lexA+ background, mutations in recF, recO or recR block both pathways. Similar results were obtained with a lexA(Def) recF strain. However, lexA(Def) recO or lexA(Def) recR strains, although unable to facilitate PriA-pol II-dependent restart, were able to perform pol V-dependent readthrough. The defects in restart attributed to mutations in recF, recO or recR were suppressed in a recA730 lexA(Def) strain expressing constitutively activated RecA (RecA*). Our data suggest that in a wild-type background, RecF, O and R are important for the induction of the SOS response and the formation of RecA*-dependent recombination intermediates necessary for PriA/Pol II-dependent replication restart. In con-trast, only RecF is required for the activation of RecA that leads to the formation of pol V (UmuD'2C) and facilitates replication readthrough.
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Affiliation(s)
- Savithri Rangarajan
- Department of Biological Sciences and Chemistry, Hedco Molecular Biology Laboratories, University of Southern California, Los Angeles, CA 90089-1340, USA
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28
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Gregg AV, McGlynn P, Jaktaji RP, Lloyd RG. Direct rescue of stalled DNA replication forks via the combined action of PriA and RecG helicase activities. Mol Cell 2002; 9:241-51. [PMID: 11864599 DOI: 10.1016/s1097-2765(02)00455-0] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The PriA protein of Escherichia coli plays a key role in the rescue of replication forks stalled on the template DNA. One attractive model of rescue relies on homologous recombination to establish a new fork via PriA-mediated loading of the DnaB replicative helicase at D loop intermediates. We provide genetic and biochemical evidence that PriA helicase activity can also rescue a stalled fork by an alternative mechanism that requires manipulation of the fork before loading of DnaB on the lagging strand template. This direct rescue depends on RecG, which unwinds forks and Holliday junctions and interconverts these structures. The combined action of PriA and RecG helicase activities may thus avoid the potential dangers of rescue pathways involving fork breakage and recombination.
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Affiliation(s)
- Amanda V Gregg
- Institute of Genetics, Queen's Medical Centre, University of Nottingham, United Kingdom
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29
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Bruand C, Farache M, McGovern S, Ehrlich SD, Polard P. DnaB, DnaD and DnaI proteins are components of the Bacillus subtilis replication restart primosome. Mol Microbiol 2001; 42:245-55. [PMID: 11679082 DOI: 10.1046/j.1365-2958.2001.02631.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Phenotypes of Bacillus subtilis priA mutants suggest that they are deficient in the restart of stalled chromosomal replication forks. The presumed activity of PriA in the restart process is to promote the assembly of a multiprotein complex, the primosome, which functions to recruit the replication fork helicase onto the DNA. We have proposed previously that three proteins involved in the initiation of replication at oriC in B. subtilis, DnaB, DnaD and DnaI, are components of the PriA primosome in this bacterium. However, the involvement of these proteins in replication restart has not yet been studied. Here, we describe dnaB mutations that suppress the phenotypes of B. subtilis priA mutants. In a representative mutant, the DnaC helicase is loaded onto single-stranded DNA in a PriA-independent, DnaD- and DnaI-dependent manner. These observations confirm that DnaB, DnaD and DnaI are primosomal proteins in B. subtilis. Moreover, their involvement in the suppression of priA phenotypes shows that they participate in replication fork restart in B. subtilis.
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Affiliation(s)
- C Bruand
- Laboratoire de Génétique Microbienne, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas cedex, France.
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30
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Abstract
The encounter of a replication fork with either a damaged DNA template, a nick in the template strand or a 'frozen' protein-DNA complex can stall the replisome and cause it to fall apart. Such an event generates a requirement for replication fork restart if the cell is going to survive. Recent evidence shows that replication fork restart is effected by the action of the recombination proteins generating a substrate for PriA-directed replication fork assembly.
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Affiliation(s)
- K J Marians
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
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