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Kannan S, Gillespie SW, Picking WL, Picking WD, Lorson CL, Singh K. Inhibitors against DNA Polymerase I Family of Enzymes: Novel Targets and Opportunities. BIOLOGY 2024; 13:204. [PMID: 38666816 PMCID: PMC11048162 DOI: 10.3390/biology13040204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 03/18/2024] [Accepted: 03/20/2024] [Indexed: 04/28/2024]
Abstract
DNA polymerases replicate cellular genomes and/or participate in the maintenance of genome integrity. DNA polymerases sharing high sequence homology with E. coli DNA polymerase I (pol I) have been grouped in Family A. Pol I participates in Okazaki fragment maturation and in bacterial genome repair. Since its discovery in 1956, pol I has been extensively studied, primarily to gain deeper insights into the mechanism of DNA replication. As research on DNA polymerases advances, many novel functions of this group of polymerases are being uncovered. For example, human DNA polymerase θ (a Family A DNA pol) has been shown to synthesize DNA using RNA as a template, a function typically attributed to retroviral reverse transcriptase. Increased interest in drug discovery against pol θ has emerged due to its roles in cancer. Likewise, Pol I family enzymes also appear attractive as drug-development targets against microbial infections. Development of antimalarial compounds targeting apicoplast apPOL, an ortholog of Pol I, further extends the targeting of this family of enzymes. Here, we summarize reported drug-development efforts against Family A polymerases and future perspective regarding these enzymes as antibiotic targets. Recently developed techniques, such as artificial intelligence, can be used to facilitate the development of new drugs.
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Affiliation(s)
- Saathvik Kannan
- Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA; (S.K.); (S.W.G.); (W.L.P.); (W.D.P.); (C.L.L.)
| | - Samuel W. Gillespie
- Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA; (S.K.); (S.W.G.); (W.L.P.); (W.D.P.); (C.L.L.)
| | - Wendy L. Picking
- Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA; (S.K.); (S.W.G.); (W.L.P.); (W.D.P.); (C.L.L.)
- Department of Veterinary Pathobiology, University of Missouri, Columbia, MO 65211, USA
| | - William D. Picking
- Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA; (S.K.); (S.W.G.); (W.L.P.); (W.D.P.); (C.L.L.)
- Department of Veterinary Pathobiology, University of Missouri, Columbia, MO 65211, USA
| | - Christian L. Lorson
- Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA; (S.K.); (S.W.G.); (W.L.P.); (W.D.P.); (C.L.L.)
- Department of Veterinary Pathobiology, University of Missouri, Columbia, MO 65211, USA
| | - Kamal Singh
- Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA; (S.K.); (S.W.G.); (W.L.P.); (W.D.P.); (C.L.L.)
- Department of Veterinary Pathobiology, University of Missouri, Columbia, MO 65211, USA
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During Translesion Synthesis, Escherichia coli DinB89 (T120P) Alters Interactions of DinB (Pol IV) with Pol III Subunit Assemblies and SSB, but Not with the β Clamp. J Bacteriol 2022; 204:e0061121. [PMID: 35285726 DOI: 10.1128/jb.00611-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Translesion synthesis (TLS) by specialized DNA polymerases (Pols) is an evolutionarily conserved mechanism for tolerating replication-blocking DNA lesions. Using the Escherichia coli dinB-encoded Pol IV as a model to understand how TLS is coordinated with the actions of the high-fidelity Pol III replicase, we previously described a novel Pol IV mutant containing a threonine 120-to-proline mutation (Pol IV-T120P) that failed to exchange places with Pol III at the replication fork in vitro as part of a Pol III-Pol IV switch. This in vitro defect correlated with the inability of Pol IV-T120P to support TLS in vivo, suggesting Pol IV gains access to the DNA, at least in part, via a Pol III-Pol IV switch. Interaction of Pol IV with the β sliding clamp and the single-stranded DNA binding protein (SSB) significantly stimulates Pol IV replication and facilitates its access to the DNA. In this work, we demonstrate that Pol IV interacts physically with Pol III. We further show that Pol IV-T120P interacts normally with the β clamp, but is impaired in interactions with the α catalytic and εθ proofreading subunits of Pol III, as well as SSB. Taken together with published work, these results provide strong support for the model in which Pol IV-Pol III and Pol IV-SSB interactions help to regulate the access of Pol IV to the DNA. Finally, we describe several additional E. coli Pol-Pol interactions, suggesting Pol-Pol interactions play fundamental roles in coordinating bacterial DNA replication, DNA repair, and TLS. IMPORTANCE Specialized DNA polymerases (Pols) capable of catalyzing translesion synthesis (TLS) generate mutations that contribute to bacterial virulence, pathoadaptation, and antimicrobial resistance. One mechanism by which the bacterial TLS Pol IV gains access to the DNA to generate mutations is by exchanging places with the bacterial Pol III replicase via a Pol III-Pol IV switch. Here, we describe multiple Pol III-Pol IV interactions and discuss evidence that these interactions are required for the Pol III-Pol IV switch. Furthermore, we describe several additional E. coli Pol-Pol interactions that may play fundamental roles in managing the actions of the different bacterial Pols in DNA replication, DNA repair, and TLS.
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Naveen V, Hsiao CD. NrdR Transcription Regulation: Global Proteome Analysis and Its Role in Escherichia coli Viability and Virulence. PLoS One 2016; 11:e0157165. [PMID: 27275780 PMCID: PMC4898720 DOI: 10.1371/journal.pone.0157165] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 05/25/2016] [Indexed: 12/16/2022] Open
Abstract
Bacterial ribonucleotide reductases (RNRs) play an important role in the synthesis of dNTPs and their expression is regulated by the transcription factors, NrdR and Fur. Recent transcriptomic studies using deletion mutants have indicated a role for NrdR in bacterial chemotaxis and in the maintenance of topoisomerase levels. However, NrdR deletion alone has no effect on bacterial growth or virulence in infected flies or in human blood cells. Furthermore, transcriptomic studies are limited to the deletion strain alone, and so are inadequate for drawing biological implications when the NrdR repressor is active or abundant. Therefore, further examination is warranted of changes in the cellular proteome in response to both NrdR overexpression, as well as deletion, to better understand its functional relevance as a bacterial transcription repressor. Here, we profile bacterial fate under conditions of overexpression and deletion of NrdR in E. coli. Biochemical assays show auxiliary zinc enhances the DNA binding activity of NrdR. We also demonstrate at the physiological level that increased nrdR expression causes a significant reduction in bacterial growth and fitness even at normal temperatures, and causes lethality at elevated temperatures. Corroborating these direct effects, global proteome analysis following NrdR overexpression showed a significant decrease in global protein expression. In parallel, studies on complementary expression of downregulated essential genes polA, eno and thiL showed partial rescue of the fitness defect caused by NrdR overexpression. Deletion of downregulated non-essential genes ygfK and trxA upon NrdR overexpression resulted in diminished bacterial growth and fitness suggesting an additional role for NrdR in regulating other genes. Moreover, in comparison with NrdR deletion, E. coli cells overexpressing NrdR showed significantly diminished adherence to human epithelial cells, reflecting decreased bacterial virulence. These results suggest that elevated expression of NrdR could be a suitable means to retard bacterial growth and virulence, as its elevated expression reduces bacterial fitness and impairs host cell adhesion.
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Affiliation(s)
- Vankadari Naveen
- Molecular Cell Biology, Taiwan International Graduate Program, Graduate Institute of Life Sciences, National Defense Medical Center and Academia Sinica, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Taiwan
| | - Chwan-Deng Hsiao
- Molecular Cell Biology, Taiwan International Graduate Program, Graduate Institute of Life Sciences, National Defense Medical Center and Academia Sinica, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, Taipei, 115, Taiwan
- * E-mail:
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A Genetic Selection for dinB Mutants Reveals an Interaction between DNA Polymerase IV and the Replicative Polymerase That Is Required for Translesion Synthesis. PLoS Genet 2015; 11:e1005507. [PMID: 26352807 PMCID: PMC4564189 DOI: 10.1371/journal.pgen.1005507] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 08/14/2015] [Indexed: 11/19/2022] Open
Abstract
Translesion DNA synthesis (TLS) by specialized DNA polymerases (Pols) is a conserved mechanism for tolerating replication blocking DNA lesions. The actions of TLS Pols are managed in part by ring-shaped sliding clamp proteins. In addition to catalyzing TLS, altered expression of TLS Pols impedes cellular growth. The goal of this study was to define the relationship between the physiological function of Escherichia coli Pol IV in TLS and its ability to impede growth when overproduced. To this end, 13 novel Pol IV mutants were identified that failed to impede growth. Subsequent analysis of these mutants suggest that overproduced levels of Pol IV inhibit E. coli growth by gaining inappropriate access to the replication fork via a Pol III-Pol IV switch that is mechanistically similar to that used under physiological conditions to coordinate Pol IV-catalyzed TLS with Pol III-catalyzed replication. Detailed analysis of one mutant, Pol IV-T120P, and two previously described Pol IV mutants impaired for interaction with either the rim (Pol IVR) or the cleft (Pol IVC) of the β sliding clamp revealed novel insights into the mechanism of the Pol III-Pol IV switch. Specifically, Pol IV-T120P retained complete catalytic activity in vitro but, like Pol IVR and Pol IVC, failed to support Pol IV TLS function in vivo. Notably, the T120P mutation abrogated a biochemical interaction of Pol IV with Pol III that was required for Pol III-Pol IV switching. Taken together, these results support a model in which Pol III-Pol IV switching involves interaction of Pol IV with Pol III, as well as the β clamp rim and cleft. Moreover, they provide strong support for the view that Pol III-Pol IV switching represents a vitally important mechanism for regulating TLS in vivo by managing access of Pol IV to the DNA. Bacterial DNA polymerase IV (Pol IV) is capable of replicating damaged DNA via a process termed translesion DNA synthesis (TLS). Pol IV-mediated TLS can be accurate or error-prone, depending on the type of DNA damage. Errors made by Pol IV contribute to antibiotic resistance and adaptation of bacterial pathogens. In addition to catalyzing TLS, overproduction of Escherichia coli Pol IV impedes growth. In the current work, we demonstrate that both of these functions rely on the ability of Pol IV to bind the β sliding processivity clamp and switch places on DNA with the replicative Pol, Pol III. This switch requires that Pol IV contact both Pol III as well as two discrete sites on the β clamp protein. Taken together, these results provide a deeper understanding of how E. coli manages the actions of Pol III and Pol IV to coordinate high fidelity replication with potentially error-prone TLS.
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Hattangady DS, Singh AK, Muthaiyan A, Jayaswal RK, Gustafson JE, Ulanov AV, Li Z, Wilkinson BJ, Pfeltz RF. Genomic, Transcriptomic and Metabolomic Studies of Two Well-Characterized, Laboratory-Derived Vancomycin-Intermediate Staphylococcus aureus Strains Derived from the Same Parent Strain. Antibiotics (Basel) 2015; 4:76-112. [PMID: 27025616 PMCID: PMC4790321 DOI: 10.3390/antibiotics4010076] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 11/20/2014] [Accepted: 12/10/2014] [Indexed: 11/16/2022] Open
Abstract
Complete genome comparisons, transcriptomic and metabolomic studies were performed on two laboratory-selected, well-characterized vancomycin-intermediate Staphylococcus aureus (VISA) derived from the same parent MRSA that have changes in cell wall composition and decreased autolysis. A variety of mutations were found in the VISA, with more in strain 13136p(-)m⁺V20 (vancomycin MIC = 16 µg/mL) than strain 13136p(-)m⁺V5 (MIC = 8 µg/mL). Most of the mutations have not previously been associated with the VISA phenotype; some were associated with cell wall metabolism and many with stress responses, notably relating to DNA damage. The genomes and transcriptomes of the two VISA support the importance of gene expression regulation to the VISA phenotype. Similarities in overall transcriptomic and metabolomic data indicated that the VISA physiologic state includes elements of the stringent response, such as downregulation of protein and nucleotide synthesis, the pentose phosphate pathway and nutrient transport systems. Gene expression for secreted virulence determinants was generally downregulated, but was more variable for surface-associated virulence determinants, although capsule formation was clearly inhibited. The importance of activated stress response elements could be seen across all three analyses, as in the accumulation of osmoprotectant metabolites such as proline and glutamate. Concentrations of potential cell wall precursor amino acids and glucosamine were increased in the VISA strains. Polyamines were decreased in the VISA, which may facilitate the accrual of mutations. Overall, the studies confirm the wide variability in mutations and gene expression patterns that can lead to the VISA phenotype.
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Affiliation(s)
- Dipti S Hattangady
- School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
| | - Atul K Singh
- School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
| | - Arun Muthaiyan
- School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
| | | | - John E Gustafson
- Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, USA.
| | - Alexander V Ulanov
- Roy J. Carver Biotechnology Center, University of Illinois at Urbana-Champaign, Urbana, IL 61807, USA.
| | - Zhong Li
- Roy J. Carver Biotechnology Center, University of Illinois at Urbana-Champaign, Urbana, IL 61807, USA.
| | - Brian J Wilkinson
- School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
| | - Richard F Pfeltz
- BD Diagnostic Systems, Microbiology Research and Development, Sparks, MD 21152, USA.
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Escherichia coli DNA polymerase IV (Pol IV), but not Pol II, dynamically switches with a stalled Pol III* replicase. J Bacteriol 2012; 194:3589-600. [PMID: 22544274 DOI: 10.1128/jb.00520-12] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The dnaN159 allele encodes a temperature-sensitive mutant form of the β sliding clamp (β159). SOS-induced levels of DNA polymerase IV (Pol IV) confer UV sensitivity upon the dnaN159 strain, while levels of Pol IV ∼4-fold higher than those induced by the SOS response severely impede its growth. Here, we used mutations in Pol IV that disrupted specific interactions with the β clamp to test our hypothesis that these phenotypes were the result of Pol IV gaining inappropriate access to the replication fork via a Pol III*-Pol IV switch relying on both the rim and cleft of the clamp. Our results clearly demonstrate that Pol IV relied on both the clamp rim and cleft interactions for these phenotypes. In contrast to the case for Pol IV, elevated levels of the other Pols, including Pol II, which was expressed at levels ∼8-fold higher than the normal SOS-induced levels, failed to impede growth of the dnaN159 strain. These findings suggest that the mechanism used by Pol IV to switch with Pol III* is distinct from those used by the other Pols. Results of experiments utilizing purified components to reconstitute the Pol III*-Pol II switch in vitro indicated that Pol II switched equally well with both a stalled and an actively replicating Pol III* in a manner that was independent of the rim contact required by Pol IV. These results provide compelling support for the Pol III*-Pol IV two-step switch model and demonstrate important mechanistic differences in how Pol IV and Pol II switch with Pol III*.
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López de Saro FJ. Regulation of interactions with sliding clamps during DNA replication and repair. Curr Genomics 2011; 10:206-15. [PMID: 19881914 PMCID: PMC2705854 DOI: 10.2174/138920209788185234] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Revised: 03/09/2009] [Accepted: 03/16/2009] [Indexed: 01/12/2023] Open
Abstract
The molecular machines that replicate the genome consist of many interacting components. Essential to the organization of the replication machinery are ring-shaped proteins, like PCNA (Proliferating Cell Nuclear Antigen) or the β- clamp, collectively named sliding clamps. They encircle the DNA molecule and slide on it freely and bidirectionally. Sliding clamps are typically associated to DNA polymerases and provide these enzymes with the processivity required to synthesize large chromosomes. Additionally, they interact with a large array of proteins that perform enzymatic reactions on DNA, targeting and orchestrating their functions. In recent years there have been a large number of studies that have analyzed the structural details of how sliding clamps interact with their ligands. However, much remains to be learned in relation to how these interactions are regulated to occur coordinately and sequentially. Since sliding clamps participate in reactions in which many different enzymes bind and then release from the clamp in an orchestrated way, it is critical to analyze how these changes in affinity take place. In this review I focus the attention on the mechanisms by which various types of enzymes interact with sliding clamps and what is known about the regulation of this binding. Especially I describe emerging paradigms on how enzymes switch places on sliding clamps during DNA replication and repair of prokaryotic and eukaryotic genomes.
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Affiliation(s)
- Francisco J López de Saro
- Laboratorio de Ecología Molecular, Centro de Astrobiología (CSIC-INTA), 28850 Torrejón de Ardoz, Madrid, Spain
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Allen JM, Simcha DM, Ericson NG, Alexander DL, Marquette JT, Van Biber BP, Troll CJ, Karchin R, Bielas JH, Loeb LA, Camps M. Roles of DNA polymerase I in leading and lagging-strand replication defined by a high-resolution mutation footprint of ColE1 plasmid replication. Nucleic Acids Res 2011; 39:7020-33. [PMID: 21622658 PMCID: PMC3167613 DOI: 10.1093/nar/gkr157] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
DNA polymerase I (pol I) processes RNA primers during lagging-strand synthesis and fills small gaps during DNA repair reactions. However, it is unclear how pol I and pol III work together during replication and repair or how extensive pol I processing of Okazaki fragments is in vivo. Here, we address these questions by analyzing pol I mutations generated through error-prone replication of ColE1 plasmids. The data were obtained by direct sequencing, allowing an accurate determination of the mutation spectrum and distribution. Pol I’s mutational footprint suggests: (i) during leading-strand replication pol I is gradually replaced by pol III over at least 1.3 kb; (ii) pol I processing of Okazaki fragments is limited to ∼20 nt and (iii) the size of Okazaki fragments is short (∼250 nt). While based on ColE1 plasmid replication, our findings are likely relevant to other pol I replicative processes such as chromosomal replication and DNA repair, which differ from ColE1 replication mostly at the recruitment steps. This mutation footprinting approach should help establish the role of other prokaryotic or eukaryotic polymerases in vivo, and provides a tool to investigate how sequence topology, DNA damage, or interactions with protein partners may affect the function of individual DNA polymerases.
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Affiliation(s)
- Jennifer M Allen
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, 1156 High Street Santa Cruz, CA 95060, USA
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Sutton MD, Duzen JM, Scouten Ponticelli SK. A single hydrophobic cleft in the Escherichia coli processivity clamp is sufficient to support cell viability and DNA damage-induced mutagenesis in vivo. BMC Mol Biol 2010; 11:102. [PMID: 21190558 PMCID: PMC3022782 DOI: 10.1186/1471-2199-11-102] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Accepted: 12/29/2010] [Indexed: 11/24/2022] Open
Abstract
Background The ubiquitous family of DnaN sliding processivity clamp proteins plays essential roles in DNA replication, DNA repair, and cell cycle progression, in part by managing the actions of the different proteins involved in these processes. Interactions of the homodimeric Escherichia coli β clamp with its known partners involves multiple surfaces, including a hydrophobic cleft located near the C-terminus of each clamp protomer. Results A mutant E. coli β clamp protein lacking a functional hydrophobic cleft (βC) complemented the temperature sensitive growth phenotype of a strain bearing the dnaN159 allele, which encodes a thermolabile mutant clamp protein (β159). Complementation was conferred by a βC/β159 heterodimer, and was observed only in the absence of the dinB gene, which encodes DNA polymerase IV (Pol IV). Furthermore, the complemented strain was proficient for umuDC (Pol V) -dependent ultraviolet light (UV) -induced mutagenesis. Conclusions Our results suggest that a single cleft in the homodimeric E. coli β sliding clamp protein is sufficient to support both cell viability, as well as Pol III, Pol IV, and Pol V function in vivo. These findings provide further support for a model in which different Pols switch places with each other on DNA using a single cleft in the clamp.
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Affiliation(s)
- Mark D Sutton
- Department of Biochemistry, and Witebsky Center for Microbial Pathogenesis and Immunology, School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, 3435 Main Street, 140 Farber Hall, Buffalo, NY 14214, USA.
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dnaX36 Mutator of Escherichia coli: effects of the {tau} subunit of the DNA polymerase III holoenzyme on chromosomal DNA replication fidelity. J Bacteriol 2010; 193:296-300. [PMID: 21036999 DOI: 10.1128/jb.01191-10] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Escherichia coli dnaX36 mutant displays a mutator effect, reflecting a fidelity function of the dnaX-encoded τ subunit of the DNA polymerase III (Pol III) holoenzyme. We have shown that this fidelity function (i) applies to both leading- and lagging-strand synthesis, (ii) is independent of Pol IV, and (iii) is limited by Pol II.
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Mutations in the Bacillus subtilis beta clamp that separate its roles in DNA replication from mismatch repair. J Bacteriol 2010; 192:3452-63. [PMID: 20453097 DOI: 10.1128/jb.01435-09] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The beta clamp is an essential replication sliding clamp required for processive DNA synthesis. The beta clamp is also critical for several additional aspects of DNA metabolism, including DNA mismatch repair (MMR). The dnaN5 allele of Bacillus subtilis encodes a mutant form of beta clamp containing the G73R substitution. Cells with the dnaN5 allele are temperature sensitive for growth due to a defect in DNA replication at 49 degrees C, and they show an increase in mutation frequency caused by a partial defect in MMR at permissive temperatures. We selected for intragenic suppressors of dnaN5 that rescued viability at 49 degrees C to determine if the DNA replication defect could be separated from the MMR defect. We isolated three intragenic suppressors of dnaN5 that restored growth at the nonpermissive temperature while maintaining an increase in mutation frequency. All three dnaN alleles encoded the G73R substitution along with one of three novel missense mutations. The missense mutations isolated were S22P, S181G, and E346K. Of these, S181G and E346K are located near the hydrophobic cleft of the beta clamp, a common site occupied by proteins that bind the beta clamp. Using several methods, we show that the increase in mutation frequency resulting from each dnaN allele is linked to a defect in MMR. Moreover, we found that S181G and E346K allowed growth at elevated temperatures and did not have an appreciable effect on mutation frequency when separated from G73R. Thus, we found that specific residue changes in the B. subtilis beta clamp separate the role of the beta clamp in DNA replication from its role in MMR.
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A model for DNA polymerase switching involving a single cleft and the rim of the sliding clamp. Proc Natl Acad Sci U S A 2009; 106:12664-9. [PMID: 19617571 DOI: 10.1073/pnas.0903460106] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The actions of Escherichia coli DNA Polymerase IV (Pol IV) in mutagenesis are managed by its interaction with the beta sliding clamp. In the structure reported by Bunting et al. [EMBO J (2003) 22:5883-5892], the C-tail of Pol IV contacts a hydrophobic cleft on the clamp, while residues V303-P305 reach over the dimer interface to contact the rim of the adjacent clamp protomer. Using mutant forms of these proteins impaired for either the rim or the cleft contacts, we determined that the rim contact was dispensable for Pol IV replication in vitro, while the cleft contact was absolutely required. Using an in vitro assay to monitor Pol III*-Pol IV switching, we determined that a single cleft on the clamp was sufficient to support the switch, and that both the rim and cleft contacts were required. Results from genetic experiments support a role for the cleft and rim contacts in Pol IV function in vivo. Taken together, our findings challenge the toolbelt model and suggest instead that Pol IV contacts the rim of the clamp adjacent to the cleft that is bound by Pol III* before gaining control of the same cleft that is bound by Pol III*.
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Coordinating DNA polymerase traffic during high and low fidelity synthesis. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1804:1167-79. [PMID: 19540941 DOI: 10.1016/j.bbapap.2009.06.010] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2009] [Revised: 06/02/2009] [Accepted: 06/02/2009] [Indexed: 02/08/2023]
Abstract
With the discovery that organisms possess multiple DNA polymerases (Pols) displaying different fidelities, processivities, and activities came the realization that mechanisms must exist to manage the actions of these diverse enzymes to prevent gratuitous mutations. Although many of the Pols encoded by most organisms are largely accurate, and participate in DNA replication and DNA repair, a sizeable fraction display a reduced fidelity, and act to catalyze potentially error-prone translesion DNA synthesis (TLS) past lesions that persist in the DNA. Striking the proper balance between use of these different enzymes during DNA replication, DNA repair, and TLS is essential for ensuring accurate duplication of the cell's genome. This review highlights mechanisms that organisms utilize to manage the actions of their different Pols. A particular emphasis is placed on discussion of current models for how different Pols switch places with each other at the replication fork during high fidelity replication and potentially error-pone TLS.
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