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Bhawsinghka N, Burkholder A, Schaaper RM. Detection of DNA replication errors and 8-oxo-dGTP-mediated mutations in E. coli by Duplex DNA Sequencing. DNA Repair (Amst) 2023; 123:103462. [PMID: 36738688 PMCID: PMC9992157 DOI: 10.1016/j.dnarep.2023.103462] [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: 10/27/2022] [Revised: 01/12/2023] [Accepted: 01/26/2023] [Indexed: 01/30/2023]
Abstract
Mutation is a phenomenon inescapable for all life-forms, including bacteria. While bacterial mutation rates are generally low due to the operation of error-avoidance systems, sometimes they are elevated by many orders of magnitude. Such a state, known as a hypermutable state, can result from exposure to stress or to harmful environments. Studies of bacterial mutation frequencies and analysis of the precise types of mutations can provide insights into the mechanisms by which mutations occur and the possible involvement of error-avoidance pathways. Several approaches have been used for this, like reporter assays involving non-essential genes or mutation accumulation over multiple generations. However, these approaches give an indirect estimation, and a more direct approach for determining mutations is desirable. With the recent development of a DNA sequencing technique known as Duplex Sequencing, it is possible to detect rare variants in a population at a frequency of 1 in 107 base pairs or less. Here, we have applied Duplex Sequencing to study spontaneous mutations in E. coli. We also investigated the production of replication errors by using a mismatch-repair defective (mutL) strain as well as oxidative-stress associated mutations using a mutT-defective strain. For DNA from a wild-type strain we obtained mutant frequencies in the range of 10-7 to 10-8 depending on the specific base-pair substitution, but we argue that these mutants merely represent a background of the system, rather than mutations that occurred in vivo. In contrast, bona-fide in vivo mutations were identified for DNA from both the mutL and mutT strains, as indicated by specific increases in base substitutions that are fully consistent with their established in vivo roles. Notably, the data reproduce the specific context effects of in vivo mutations as well as the leading vs. lagging strand bias among DNA replication errors.
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Affiliation(s)
- Niketa Bhawsinghka
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
| | - Adam Burkholder
- Office of Environmental Science Cyberinfrastructure, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
| | - Roel M Schaaper
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.
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2
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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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3
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Spontaneous Polyploids and Antimutators Compete During the Evolution of Saccharomyces cerevisiae Mutator Cells. Genetics 2020; 215:959-974. [PMID: 32513814 PMCID: PMC7404223 DOI: 10.1534/genetics.120.303333] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 05/22/2020] [Indexed: 02/02/2023] Open
Abstract
Mutations affecting DNA polymerase exonuclease domains or mismatch repair (MMR) generate "mutator" phenotypes capable of driving tumorigenesis. Cancers with both defects exhibit an explosive increase in mutation burden that appears to reach a threshold, consistent with selection acting against further mutation accumulation. In Saccharomyces cerevisiae haploid yeast, simultaneous defects in polymerase proofreading and MMR select for "antimutator" mutants that suppress the mutator phenotype. We report here that spontaneous polyploids also escape this "error-induced extinction" and routinely outcompete antimutators in evolved haploid cultures. We performed similar experiments to explore how diploid yeast adapt to the mutator phenotype. We first evolved cells with homozygous mutations affecting polymerase δ proofreading and MMR, which we anticipated would favor tetraploid emergence. While tetraploids arose with a low frequency, in most cultures, a single antimutator clone rose to prominence carrying biallelic mutations affecting the polymerase mutator alleles. Variation in mutation rate between subclones from the same culture suggests that there exists continued selection pressure for additional antimutator alleles. We then evolved diploid yeast modeling MMR-deficient cancers with the most common heterozygous exonuclease domain mutation (POLE-P286R). Although these cells grew robustly, within 120 generations, all subclones carried truncating or nonsynonymous mutations in the POLE-P286R homologous allele (pol2-P301R) that suppressed the mutator phenotype as much as 100-fold. Independent adaptive events in the same culture were common. Our findings suggest that analogous tumor cell populations may adapt to the threat of extinction by polyclonal mutations that neutralize the POLE mutator allele and preserve intratumoral genetic diversity for future adaptation.
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4
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Sidorova A, Levashova N, Garaeva A, Tverdislov V. A percolation model of natural selection. Biosystems 2020; 193-194:104120. [PMID: 32092352 DOI: 10.1016/j.biosystems.2020.104120] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 01/29/2020] [Accepted: 02/15/2020] [Indexed: 12/13/2022]
Abstract
A new approach has been proposed and developed: the selection of optimal variants in the evolutionary mutation flow is considered as an analogue of a percolation filter. Interaction of mutations in a series of generations and random processes of drift determine the collective behavior of nodes (individuals - carriers and converters of mutations) and bonds (mutations) in the space of percolation lattice. It is shown that the choice of the development trajectory at the population level depends on the spectrum of supporting and prohibiting mutations under the influence of conjugate deterministic and random factors. From the point of view of the fluctuation-bifurcation process, new concepts of the lower and upper thresholds of the percolation selection grid are defined in the hierarchical structure of speciation. The upper threshold determines the state of self-organized criticality, which, when overcome, leads to irreversible self-organization processes in the population caused by the accumulation of mutations.
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Affiliation(s)
- Alla Sidorova
- Department of Biophysics, Faculty of Physics, M.V.Lomonosov Moscow State University. Moscow, 119991, Russia.
| | - Natalia Levashova
- Department of Mathematics, Faculty of Physics, M.V.Lomonosov Moscow State University. Moscow, 119991, Russia.
| | - Anastasia Garaeva
- Department of Biophysics, Faculty of Physics, M.V.Lomonosov Moscow State University. Moscow, 119991, Russia.
| | - Vsevolod Tverdislov
- Department of Biophysics, Faculty of Physics, M.V.Lomonosov Moscow State University. Moscow, 119991, Russia.
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5
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Spohn R, Daruka L, Lázár V, Martins A, Vidovics F, Grézal G, Méhi O, Kintses B, Számel M, Jangir PK, Csörgő B, Györkei Á, Bódi Z, Faragó A, Bodai L, Földesi I, Kata D, Maróti G, Pap B, Wirth R, Papp B, Pál C. Integrated evolutionary analysis reveals antimicrobial peptides with limited resistance. Nat Commun 2019; 10:4538. [PMID: 31586049 PMCID: PMC6778101 DOI: 10.1038/s41467-019-12364-6] [Citation(s) in RCA: 191] [Impact Index Per Article: 38.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 08/27/2019] [Indexed: 12/24/2022] Open
Abstract
Antimicrobial peptides (AMPs) are promising antimicrobials, however, the potential of bacterial resistance is a major concern. Here we systematically study the evolution of resistance to 14 chemically diverse AMPs and 12 antibiotics in Escherichia coli. Our work indicates that evolution of resistance against certain AMPs, such as tachyplesin II and cecropin P1, is limited. Resistance level provided by point mutations and gene amplification is very low and antibiotic-resistant bacteria display no cross-resistance to these AMPs. Moreover, genomic fragments derived from a wide range of soil bacteria confer no detectable resistance against these AMPs when introduced into native host bacteria on plasmids. We have found that simple physicochemical features dictate bacterial propensity to evolve resistance against AMPs. Our work could serve as a promising source for the development of new AMP-based therapeutics less prone to resistance, a feature necessary to avoid any possible interference with our innate immune system.
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Affiliation(s)
- Réka Spohn
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
| | - Lejla Daruka
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- Doctoral School of Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Viktória Lázár
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa, Israel
| | - Ana Martins
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
| | - Fanni Vidovics
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
| | - Gábor Grézal
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- HCEMM-BRC Metabolic Systems Biology Lab, Szeged, Hungary
| | - Orsolya Méhi
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
| | - Bálint Kintses
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- Department of Biochemistry and Molecular Biology, University of Szeged, Szeged, Hungary
| | - Mónika Számel
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- Doctoral School of Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Pramod K Jangir
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- Doctoral School of Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Bálint Csörgő
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- University of California, San Francisco, Department of Microbiology and Immunology, San Francisco, CA, USA
| | - Ádám Györkei
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- HCEMM-BRC Metabolic Systems Biology Lab, Szeged, Hungary
| | - Zoltán Bódi
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
| | - Anikó Faragó
- Doctoral School of Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
- Department of Biochemistry and Molecular Biology, University of Szeged, Szeged, Hungary
| | - László Bodai
- Department of Biochemistry and Molecular Biology, University of Szeged, Szeged, Hungary
| | - Imre Földesi
- Department of Laboratory Medicine, University of Szeged, Szeged, Hungary
| | - Diána Kata
- Department of Laboratory Medicine, University of Szeged, Szeged, Hungary
| | - Gergely Maróti
- Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
| | - Bernadett Pap
- Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
| | - Roland Wirth
- Department of Biotechnology, University of Szeged, Szeged, Hungary
| | - Balázs Papp
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary
- HCEMM-BRC Metabolic Systems Biology Lab, Szeged, Hungary
| | - Csaba Pál
- Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre, Szeged, Hungary.
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6
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Walsh E, Henrikus SS, Vaisman A, Makiela-Dzbenska K, Armstrong TJ, Łazowski K, McDonald JP, Goodman MF, van Oijen AM, Jonczyk P, Fijalkowska IJ, Robinson A, Woodgate R. Role of RNase H enzymes in maintaining genome stability in Escherichia coli expressing a steric-gate mutant of pol V ICE391. DNA Repair (Amst) 2019; 84:102685. [PMID: 31543434 DOI: 10.1016/j.dnarep.2019.102685] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 07/31/2019] [Accepted: 08/03/2019] [Indexed: 11/18/2022]
Abstract
pol VICE391 (RumA'2B) is a low-fidelity polymerase that promotes considerably higher levels of spontaneous "SOS-induced" mutagenesis than the related E. coli pol V (UmuD'2C). The molecular basis for the enhanced mutagenesis was previously unknown. Using single molecule fluorescence microscopy to visualize pol V enzymes, we discovered that the elevated levels of mutagenesis are likely due, in part, to prolonged binding of RumB to genomic DNA leading to increased levels of DNA synthesis compared to UmuC. We have generated a steric gate pol VICE391 variant (pol VICE391_Y13A) that readily misincorporates ribonucleotides into the E. coli genome and have used the enzyme to investigate the molecular mechanisms of Ribonucleotide Excision Repair (RER) under conditions of increased ribonucleotide-induced stress. To do so, we compared the extent of spontaneous mutagenesis promoted by pol V and pol VICE391 to that of their respective steric gate variants. Levels of mutagenesis promoted by the steric gate variants that are lower than that of the wild-type enzyme are indicative of active RER that removes misincorporated ribonucleotides, but also misincorporated deoxyribonucleotides from the genome. Using such an approach, we confirmed that RNase HII plays a pivotal role in RER. In the absence of RNase HII, Nucleotide Excision Repair (NER) proteins help remove misincorporated ribonucleotides. However, significant RER occurs in the absence of RNase HII and NER. Most of the RNase HII and NER-independent RER occurs on the lagging strand during genome duplication. We suggest that this is most likely due to efficient RNase HI-dependent RER which recognizes the polyribonucleotide tracts generated by pol VICE391_Y13A. These activities are critical for the maintenance of genomic integrity when RNase HII is overwhelmed, or inactivated, as ΔrnhB or ΔrnhB ΔuvrA strains expressing pol VICE391_Y13A exhibit genome and plasmid instability in the absence of RNase HI.
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Affiliation(s)
- Erin Walsh
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA
| | - Sarah S Henrikus
- Molecular Horizons Institute and School of Chemistry and Biomolecular Science, University of Wollongong, Australia; Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Alexandra Vaisman
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA
| | | | - Thomas J Armstrong
- Molecular Horizons Institute and School of Chemistry and Biomolecular Science, University of Wollongong, Australia; Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Krystian Łazowski
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - John P McDonald
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA
| | - Myron F Goodman
- Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089-2910 USA
| | - Antoine M van Oijen
- Molecular Horizons Institute and School of Chemistry and Biomolecular Science, University of Wollongong, Australia; Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Piotr Jonczyk
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Iwona J Fijalkowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Andrew Robinson
- Molecular Horizons Institute and School of Chemistry and Biomolecular Science, University of Wollongong, Australia; Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Roger Woodgate
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, USA.
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7
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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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8
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The Spectrum of Replication Errors in the Absence of Error Correction Assayed Across the Whole Genome of Escherichia coli. Genetics 2018; 209:1043-1054. [PMID: 29907648 DOI: 10.1534/genetics.117.300515] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 06/14/2018] [Indexed: 11/18/2022] Open
Abstract
When the DNA polymerase that replicates the Escherichia coli chromosome, DNA polymerase III, makes an error, there are two primary defenses against mutation: proofreading by the ϵ subunit of the holoenzyme and mismatch repair. In proofreading-deficient strains, mismatch repair is partially saturated and the cell's response to DNA damage, the SOS response, may be partially induced. To investigate the nature of replication errors, we used mutation accumulation experiments and whole-genome sequencing to determine mutation rates and mutational spectra across the entire chromosome of strains deficient in proofreading, mismatch repair, and the SOS response. We report that a proofreading-deficient strain has a mutation rate 4000-fold greater than wild-type strains. While the SOS response may be induced in these cells, it does not contribute to the mutational load. Inactivating mismatch repair in a proofreading-deficient strain increases the mutation rate another 1.5-fold. DNA polymerase has a bias for converting G:C to A:T base pairs, but proofreading reduces the impact of these mutations, helping to maintain the genomic G:C content. These findings give an unprecedented view of how polymerase and error-correction pathways work together to maintain E. coli's low mutation rate of 1 per 1000 generations.
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9
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High-accuracy lagging-strand DNA replication mediated by DNA polymerase dissociation. Proc Natl Acad Sci U S A 2018; 115:4212-4217. [PMID: 29610333 DOI: 10.1073/pnas.1720353115] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The fidelity of DNA replication is a critical factor in the rate at which cells incur mutations. Due to the antiparallel orientation of the two chromosomal DNA strands, one strand (leading strand) is replicated in a mostly processive manner, while the other (lagging strand) is synthesized in short sections called Okazaki fragments. A fundamental question that remains to be answered is whether the two strands are copied with the same intrinsic fidelity. In most experimental systems, this question is difficult to answer, as the replication complex contains a different DNA polymerase for each strand, such as, for example, DNA polymerases δ and ε in eukaryotes. Here we have investigated this question in the bacterium Escherichia coli, in which the replicase (DNA polymerase III holoenzyme) contains two copies of the same polymerase (Pol III, the dnaE gene product), and hence the two strands are copied by the same polymerase. Our in vivo mutagenesis data indicate that the two DNA strands are not copied with the same accuracy, and that, remarkably, the lagging strand has the highest fidelity. We postulate that this effect results from the greater dissociative character of the lagging-strand polymerase, which provides additional options for error removal. Our conclusion is strongly supported by results with dnaE antimutator polymerases characterized by increased dissociation rates.
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10
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Normally lethal amino acid substitutions suppress an ultramutator DNA Polymerase δ variant. Sci Rep 2017; 7:46535. [PMID: 28417960 PMCID: PMC5394481 DOI: 10.1038/srep46535] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 03/22/2017] [Indexed: 02/06/2023] Open
Abstract
In yeast, the pol3-01,L612M double mutant allele, which causes defects in DNA polymerase delta (Pol δ) proofreading (pol3-01) and nucleotide selectivity (pol3-L612M), confers an “ultramutator” phenotype that rapidly drives extinction of haploid and diploid MMR-proficient cells. Here, we investigate antimutator mutations that encode amino acid substitutions in Pol δ that suppress this lethal phenotype. We find that most of the antimutator mutations individually suppress the pol3-01 and pol3-L612M mutator phenotypes. The locations of many of the amino acid substitutions in Pol δ resemble those of previously identified antimutator substitutions; however, two novel mutations encode substitutions (R674G and Q697R) of amino acids in the fingers domain that coordinate the incoming dNTP. These mutations are lethal without pol3-L612M and markedly change the mutation spectra produced by the pol3-01,L612M mutator allele, suggesting that they alter nucleotide selection to offset the pol3-L612M mutator phenotype. Consistent with this hypothesis, mutations and drug treatments that perturb dNTP pool levels disproportionately influence the viability of pol3-L612M,R674G and pol3-L612M,Q697R cells. Taken together, our findings suggest that mutation rate can evolve through genetic changes that alter the balance of dNTP binding and dissociation from DNA polymerases.
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11
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Hussain S. A new conceptual framework for investigating complex genetic disease. Front Genet 2015; 6:327. [PMID: 26583033 PMCID: PMC4631989 DOI: 10.3389/fgene.2015.00327] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 10/21/2015] [Indexed: 01/17/2023] Open
Abstract
Some common diseases are known to have an inherited component, however, their population- and familial-incidence patterns do not conform to any known monogenic Mendelian pattern of inheritance and instead they are currently much better explained if an underlying polygenic architecture is posited. Studies that have attempted to identify the causative genetic factors have been designed on this polygenic framework, but so far the yield has been largely unsatisfactory. Based on accumulating recent observations concerning the roles of somatic mosaicism in disease, in this article a second framework which posits a single gene-two hit model which can be modulated by a mutator/anti-mutator genetic background is suggested. I discuss whether such a model can be considered a viable alternative based on current knowledge, its advantages over the current polygenic framework, and describe practical routes via which the new framework can be investigated.
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Affiliation(s)
- Shobbir Hussain
- Department of Biology and Biochemistry, University of BathBath, UK
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12
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Mutations that Separate the Functions of the Proofreading Subunit of the Escherichia coli Replicase. G3-GENES GENOMES GENETICS 2015; 5:1301-11. [PMID: 25878065 PMCID: PMC4478557 DOI: 10.1534/g3.115.017285] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
The dnaQ gene of Escherichia coli encodes the ε subunit of DNA polymerase III, which provides the 3′ → 5′ exonuclease proofreading activity of the replicative polymerase. Prior studies have shown that loss of ε leads to high mutation frequency, partially constitutive SOS, and poor growth. In addition, a previous study from our laboratory identified dnaQ knockout mutants in a screen for mutants specifically defective in the SOS response after quinolone (nalidixic acid) treatment. To explain these results, we propose a model whereby, in addition to proofreading, ε plays a distinct role in replisome disassembly and/or processing of stalled replication forks. To explore this model, we generated a pentapeptide insertion mutant library of the dnaQ gene, along with site-directed mutants, and screened for separation of function mutants. We report the identification of separation of function mutants from this screen, showing that proofreading function can be uncoupled from SOS phenotypes (partially constitutive SOS and the nalidixic acid SOS defect). Surprisingly, the two SOS phenotypes also appear to be separable from each other. These findings support the hypothesis that ε has additional roles aside from proofreading. Identification of these mutants, especially those with normal proofreading but SOS phenotype(s), also facilitates the study of the role of ε in SOS processes without the confounding results of high mutator activity associated with dnaQ knockout mutants.
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Abstract
Genetic defects in DNA polymerase accuracy, proofreading, or mismatch repair (MMR) induce mutator phenotypes that accelerate adaptation of microbes and tumor cells. Certain combinations of mutator alleles synergistically increase mutation rates to levels that drive extinction of haploid cells. The maximum tolerated mutation rate of diploid cells is unknown. Here, we define the threshold for replication error-induced extinction (EEX) of diploid Saccharomyces cerevisiae. Double-mutant pol3 alleles that carry mutations for defective DNA polymerase-δ proofreading (pol3-01) and accuracy (pol3-L612M or pol3-L612G) induce strong mutator phenotypes in heterozygous diploids (POL3/pol3-01,L612M or POL3/pol3-01,L612G). Both pol3-01,L612M and pol3-01,L612G alleles are lethal in the homozygous state; cells with pol3-01,L612M divide up to 10 times before arresting at random stages in the cell cycle. Antimutator eex mutations in the pol3 alleles suppress this lethality (pol3-01,L612M,eex or pol3-01,L612G,eex). MMR defects synergize with pol3-01,L612M,eex and pol3-01,L612G,eex alleles, increasing mutation rates and impairing growth. Conversely, inactivation of the Dun1 S-phase checkpoint kinase suppresses strong pol3-01,L612M,eex and pol3-01,L612G,eex mutator phenotypes as well as the lethal pol3-01,L612M phenotype. Our results reveal that the lethal error threshold in diploids is 10 times higher than in haploids and likely determined by homozygous inactivation of essential genes. Pronounced loss of fitness occurs at mutation rates well below the lethal threshold, suggesting that mutator-driven cancers may be susceptible to drugs that exacerbate replication errors.
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Gawel D, Fijalkowska IJ, Jonczyk P, Schaaper RM. Effect of dNTP pool alterations on fidelity of leading and lagging strand DNA replication in E. coli. Mutat Res 2013; 759:22-8. [PMID: 24269257 DOI: 10.1016/j.mrfmmm.2013.11.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 11/02/2013] [Accepted: 11/09/2013] [Indexed: 11/17/2022]
Abstract
The fidelity with which organisms replicate their chromosomal DNA is of considerable interest. Detailed studies in the bacterium Escherichia coli have indicated that the fidelity of leading- and lagging-strand DNA replication is not the same, based on experiments in which the orientation of certain mutational targets on the chromosome was inverted relative to the movement of the replication fork: different mutation rates for several base-pair substitutions were observed depending on this orientation. While these experiments are indicative of differential replication fidelity in the two strands, a conclusion whether leading or lagging strand is the more accurate depends on knowledge of the primary mispairing error responsible for the base substitutions in question. A broad analysis of in vitro base-pairing preferences of DNA polymerases led us to propose that lagging-strand is the more accurate strand. In the present work, we present more direct in vivo evidence in support of this proposal. We determine the orientation dependence of mutant frequencies in ndk and dcd strains, which carry defined dNTP pool alterations. As these pool alterations lead to predictable effects on the array of possible mispairing errors, they mark the strands in which the observed errors occur. The combined results support the proposed higher accuracy of lagging-strand replication in E. coli.
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Affiliation(s)
- Damian Gawel
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland; Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, United States.
| | - Iwona J Fijalkowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Piotr Jonczyk
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Roel M Schaaper
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, United States
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15
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Hypermutability and error catastrophe due to defects in ribonucleotide reductase. Proc Natl Acad Sci U S A 2013; 110:18596-601. [PMID: 24167285 DOI: 10.1073/pnas.1310849110] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The enzyme ribonucleotide reductase (RNR) plays a critical role in the production of deoxynucleoside-5'-triphosphates (dNTPs), the building blocks for DNA synthesis and replication. The levels of the cellular dNTPs are tightly controlled, in large part through allosteric control of RNR. One important reason for controlling the dNTPs relates to their ability to affect the fidelity of DNA replication and, hence, the cellular mutation rate. We have previously isolated a set of mutants of Escherichia coli RNR that are characterized by altered dNTP pools and increased mutation rates (mutator mutants). Here, we show that one particular set of RNR mutants, carrying alterations at the enzyme's allosteric specificity site, is characterized by relatively modest dNTP pool deviations but exceptionally strong mutator phenotypes, when measured in a mutational forward assay (>1,000-fold increases). We provide evidence indicating that this high mutability is due to a saturation of the DNA mismatch repair system, leading to hypermutability and error catastrophe. The results indicate that, surprisingly, even modest deviations of the cellular dNTP pools, particularly when the pool deviations promote particular types of replication errors, can have dramatic consequences for mutation rates.
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16
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Reduction of dNTP levels enhances DNA replication fidelity in vivo. DNA Repair (Amst) 2013; 12:300-5. [PMID: 23433812 DOI: 10.1016/j.dnarep.2013.01.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Revised: 01/25/2013] [Accepted: 01/31/2013] [Indexed: 11/23/2022]
Abstract
ATP is the most important energy source for the maintenance and growth of living cells. Here we report that the impairment of the aerobic respiratory chain by inactivation of the ndh gene, or the inhibition of glycolysis with arsenate, both of which reduce intracellular ATP, result in a significant decrease in spontaneous mutagenesis in Escherichia coli. The genetic analyses and mutation spectra in the ndh strain revealed that the decrease in spontaneous mutagenesis resulted from an enhanced accuracy of the replicative DNA polymerase. Quantification of the dNTP content in the ndh mutant cells and in the arsenate-treated cells showed reduction of the dNTP pool, which could explain the observed broad antimutator effects. In conclusion, our work indicates that the cellular energy supply could affect spontaneous mutation rates and that a reduction of the dNTP levels can be antimutagenic.
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17
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Emergence of DNA polymerase ε antimutators that escape error-induced extinction in yeast. Genetics 2013; 193:751-70. [PMID: 23307893 DOI: 10.1534/genetics.112.146910] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
DNA polymerases (Pols) ε and δ perform the bulk of yeast leading- and lagging-strand DNA synthesis. Both Pols possess intrinsic proofreading exonucleases that edit errors during polymerization. Rare errors that elude proofreading are extended into duplex DNA and excised by the mismatch repair (MMR) system. Strains that lack Pol proofreading or MMR exhibit a 10- to 100-fold increase in spontaneous mutation rate (mutator phenotype), and inactivation of both Pol δ proofreading (pol3-01) and MMR is lethal due to replication error-induced extinction (EEX). It is unclear whether a similar synthetic lethal relationship exists between defects in Pol ε proofreading (pol2-4) and MMR. Using a plasmid-shuffling strategy in haploid Saccharomyces cerevisiae, we observed synthetic lethality of pol2-4 with alleles that completely abrogate MMR (msh2Δ, mlh1Δ, msh3Δ msh6Δ, or pms1Δ mlh3Δ) but not with partial MMR loss (msh3Δ, msh6Δ, pms1Δ, or mlh3Δ), indicating that high levels of unrepaired Pol ε errors drive extinction. However, variants that escape this error-induced extinction (eex mutants) frequently emerged. Five percent of pol2-4 msh2Δ eex mutants encoded second-site changes in Pol ε that reduced the pol2-4 mutator phenotype between 3- and 23-fold. The remaining eex alleles were extragenic to pol2-4. The locations of antimutator amino-acid changes in Pol ε and their effects on mutation spectra suggest multiple mechanisms of mutator suppression. Our data indicate that unrepaired leading- and lagging-strand polymerase errors drive extinction within a few cell divisions and suggest that there are polymerase-specific pathways of mutator suppression. The prevalence of suppressors extragenic to the Pol ε gene suggests that factors in addition to proofreading and MMR influence leading-strand DNA replication fidelity.
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18
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Schaaper RM, Mathews CK. Mutational consequences of dNTP pool imbalances in E. coli. DNA Repair (Amst) 2012; 12:73-9. [PMID: 23218950 DOI: 10.1016/j.dnarep.2012.10.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2012] [Revised: 10/30/2012] [Accepted: 10/31/2012] [Indexed: 10/27/2022]
Abstract
The accuracy of DNA synthesis depends on the accuracy of the polymerase as well as the quality and concentration(s) of the available 5'-deoxynucleoside-triphosphate DNA precursors (dNTPs). The relationships between dNTPs and error rates have been studied in vitro, but only limited insights exist into these correlations during in vivo replication. We have investigated this issue in the bacterium Escherichia coli by analyzing the mutational properties of dcd and ndk strains. These strains, defective in dCTP deaminase and nucleoside diphosphate kinase, respectively, are characterized by both disturbances of dNTP pools and a mutator phenotype. ndk strains have been studied before, but were included in this study, as controversies exist regarding the source of its mutator phenotype. We show that dcd strains suffer from increased intracellular levels of dCTP (4-fold) and reduced levels of dGTP (2-fold), while displaying, as measured using a set of lacZ reversion markers in a mismatch-repair defective (mutL) background, a strong mutator effect for G·C→T·A and A·T→T·A transversions (27- and 42-fold enhancement, respectively). In contrast, ndk strains possess a lowered dATP level (4-fold) and modestly enhanced dCTP level (2-fold), while its mutator effect is specific for just the A·T→T·A transversions. The two strains also display differential mutability for rifampicin-resistant mutants. Overall, our analysis reveals for both strains a satisfactory correlation between dNTP pool alterations and the replication error rates, and also suggests that a minimal explanation for the ndk mutator does not require assumptions beyond the predicted effect of the dNTP pools.
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Affiliation(s)
- Roel M Schaaper
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, 111 TW Alexander Drive, Research Triangle Park, NC 27709, USA.
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19
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The Evolution of Low Mutation Rates in Experimental Mutator Populations of Saccharomyces cerevisiae. Curr Biol 2012; 22:1235-40. [DOI: 10.1016/j.cub.2012.04.056] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2011] [Revised: 02/01/2012] [Accepted: 04/26/2012] [Indexed: 01/05/2023]
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20
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Fijalkowska IJ, Schaaper RM, Jonczyk P. DNA replication fidelity in Escherichia coli: a multi-DNA polymerase affair. FEMS Microbiol Rev 2012; 36:1105-21. [PMID: 22404288 DOI: 10.1111/j.1574-6976.2012.00338.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Revised: 02/29/2012] [Accepted: 03/01/2012] [Indexed: 12/21/2022] Open
Abstract
High accuracy (fidelity) of DNA replication is important for cells to preserve the genetic identity and to prevent the accumulation of deleterious mutations. The error rate during DNA replication is as low as 10(-9) to 10(-11) errors per base pair. How this low level is achieved is an issue of major interest. This review is concerned with the mechanisms underlying the fidelity of the chromosomal replication in the model system Escherichia coli by DNA polymerase III holoenzyme, with further emphasis on participation of the other, accessory DNA polymerases, of which E. coli contains four (Pols I, II, IV, and V). Detailed genetic analysis of mutation rates revealed that (1) Pol II has an important role as a back-up proofreader for Pol III, (2) Pols IV and V do not normally contribute significantly to replication fidelity, but can readily do so under conditions of elevated expression, (3) participation of Pols IV and V, in contrast to that of Pol II, is specific to the lagging strand, and (4) Pol I also makes a lagging-strand-specific fidelity contribution, limited, however, to the faithful filling of the Okazaki fragment gaps. The fidelity role of the Pol III τ subunit is also reviewed.
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Affiliation(s)
- Iwona J Fijalkowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
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21
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Ahluwalia D, Bienstock RJ, Schaaper RM. Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates. DNA Repair (Amst) 2012; 11:480-7. [PMID: 22417940 DOI: 10.1016/j.dnarep.2012.02.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2011] [Revised: 01/30/2012] [Accepted: 02/10/2012] [Indexed: 10/28/2022]
Abstract
Ribonucleotide reductase (RNR) is the enzyme critically responsible for the production of the 5'-deoxynucleoside-triphosphates (dNTPs), the direct precursors for DNA synthesis. The dNTP levels are tightly controlled to permit high efficiency and fidelity of DNA synthesis. Much of this control occurs at the level of the RNR by feedback processes, but a detailed understanding of these mechanisms is still lacking. Using a genetic approach in the bacterium Escherichia coli, a paradigm for the class Ia RNRs, we isolated 23 novel RNR mutants displaying elevated mutation rates along with altered dNTP levels. The responsible amino-acid substitutions in RNR reside in three different regions: (i) the (d)ATP-binding activity domain, (ii) a novel region in the small subunit adjacent to the activity domain, and (iii) the dNTP-binding specificity site, several of which are associated with different dNTP pool alterations and different mutational outcomes. These mutants provide new insight into the precise mechanisms by which RNR is regulated and how dNTP pool disturbances resulting from defects in RNR can lead to increased mutation.
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Affiliation(s)
- Deepti Ahluwalia
- Laboratory of Molecular Genetics, National Institute of Environmental and Health Sciences, 111 TW Alexander Drive, Research Triangle Park, NC 27709, USA
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22
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Abstract
Evolution balances DNA replication speed and accuracy to optimize replicative fitness and genetic stability. There is no selective pressure to improve DNA replication fidelity beyond the background mutation rate from other sources, such as DNA damage. However, DNA polymerases remain amenable to amino acid substitutions that lower intrinsic error rates. Here, we review these 'antimutagenic' changes in DNA polymerases and discuss what they reveal about mechanisms of replication fidelity. Pioneering studies with bacteriophage T4 DNA polymerase (T4 Pol) established the paradigm that antimutator amino acid substitutions reduce replication errors by increasing proofreading efficiency at the expense of polymerase processivity. The discoveries of antimutator substitutions in proofreading-deficient 'mutator' derivatives of bacterial Pols I and III and yeast Pol δ suggest there must be additional antimutagenic mechanisms. Remarkably, many of the affected amino acid positions from Pol I, Pol III, and Pol δ are similar to the original T4 Pol substitutions. The locations of antimutator substitutions within DNA polymerase structures suggest that they may increase nucleotide selectivity and/or promote dissociation of primer termini from polymerases poised for misincorporation, leading to expulsion of incorrect nucleotides. If misincorporation occurs, enhanced primer dissociation from polymerase domains may improve proofreading in cis by an intrinsic exonuclease or in trans by alternate cellular proofreading activities. Together, these studies reveal that natural selection can readily restore replication error rates to sustainable levels following an adaptive mutator phenotype.
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Affiliation(s)
- Alan J Herr
- Department of Pathology, University of Washington, Seattle, USA
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23
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Herr AJ, Ogawa M, Lawrence NA, Williams LN, Eggington JM, Singh M, Smith RA, Preston BD. Mutator suppression and escape from replication error-induced extinction in yeast. PLoS Genet 2011; 7:e1002282. [PMID: 22022273 PMCID: PMC3188538 DOI: 10.1371/journal.pgen.1002282] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Accepted: 07/21/2011] [Indexed: 11/23/2022] Open
Abstract
Cells rely on a network of conserved pathways to govern DNA replication fidelity. Loss of polymerase proofreading or mismatch repair elevates spontaneous mutation and facilitates cellular adaptation. However, double mutants are inviable, suggesting that extreme mutation rates exceed an error threshold. Here we combine alleles that affect DNA polymerase δ (Pol δ) proofreading and mismatch repair to define the maximal error rate in haploid yeast and to characterize genetic suppressors of mutator phenotypes. We show that populations tolerate mutation rates 1,000-fold above wild-type levels but collapse when the rate exceeds 10−3 inactivating mutations per gene per cell division. Variants that escape this error-induced extinction (eex) rapidly emerge from mutator clones. One-third of the escape mutants result from second-site changes in Pol δ that suppress the proofreading-deficient phenotype, while two-thirds are extragenic. The structural locations of the Pol δ changes suggest multiple antimutator mechanisms. Our studies reveal the transient nature of eukaryotic mutators and show that mutator phenotypes are readily suppressed by genetic adaptation. This has implications for the role of mutator phenotypes in cancer. Organisms strike a balance between genetic continuity and change. Most cells are well adapted to their niches and therefore invest heavily in mechanisms that maintain accurate DNA replication. When cell populations are confronted with changing environmental conditions, “mutator” clones with high mutation rates emerge and readily adapt to the new conditions by rapidly acquiring beneficial mutations. However, deleterious mutations also accumulate, raising the question: what level of mutational burden can cell populations sustain before collapsing? Here we experimentally determine the maximal mutation rate in haploid yeast. We observe that yeast can withstand a 1,000-fold increase in mutation rate without losing colony forming capacity. Yet no strains survive a 10,000-fold increase in mutation rate. Escape mutants with an “anti-mutator” phenotype frequently emerge from cell populations undergoing this error-induced extinction. The diversity of antimutator changes suggests that strong mutator phenotypes in nature may be inherently transient, ensuring that rapid adaptation is followed by genetic attenuation which preserves the beneficial, adaptive mutations. These observations are relevant to microbial populations during infection as well as the somatic evolution of cancer cells.
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Affiliation(s)
- Alan J. Herr
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Masanori Ogawa
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Nicole A. Lawrence
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Lindsey N. Williams
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Julie M. Eggington
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Mallika Singh
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Robert A. Smith
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Bradley D. Preston
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
- * E-mail: E-mail:
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24
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Proofreading deficiency of Pol I increases the levels of spontaneous rpoB mutations in E. coli. Mutat Res 2011; 712:28-32. [PMID: 21459099 DOI: 10.1016/j.mrfmmm.2011.03.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 03/07/2011] [Accepted: 03/24/2011] [Indexed: 11/23/2022]
Abstract
The fidelity role of DNA polymerase I in chromosomal DNA replication in E. coli was investigated using the rpoB forward target. These experiments indicated that in a strain carrying a proofreading-exonuclease-defective form of Pol I (polAexo mutant) the frequency of rpoB mutations increased by about 2-fold, consistent with a model that the fidelity of DNA polymerase I is important in controlling the overall fidelity of chromosomal DNA replication. DNA sequencing of rpoB mutants revealed that the Pol I exonuclease deficiency lead to an increase in a variety of base-substitution mutations. A polAexo mutator effect was also observed in strains defective in DNA mismatch repair and carrying the dnaE915 antimutator allele. Overall, the data are consistent with a proposed role of Pol I in the faithful completion of Okazaki fragment gaps at the replication fork.
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25
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Reha-Krantz LJ. DNA polymerase proofreading: Multiple roles maintain genome stability. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1049-63. [DOI: 10.1016/j.bbapap.2009.06.012] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2009] [Revised: 06/10/2009] [Accepted: 06/12/2009] [Indexed: 11/16/2022]
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26
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Affiliation(s)
- R Jayaraman
- R. H. 35, Palaami Enclave, New Natham Road, Madurai 625 014, India.
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27
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Makiela-Dzbenska K, Jaszczur M, Banach-Orlowska M, Jonczyk P, Schaaper RM, Fijalkowska IJ. Role of Escherichia coli DNA polymerase I in chromosomal DNA replication fidelity. Mol Microbiol 2009; 74:1114-27. [PMID: 19843230 DOI: 10.1111/j.1365-2958.2009.06921.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have investigated the possible role of Escherichia coli DNA polymerase (Pol) I in chromosomal replication fidelity. This was done by substituting the chromosomal polA gene by the polAexo variant containing an inactivated 3'-->5' exonuclease, which serves as a proofreader for this enzyme's misinsertion errors. Using this strain, activities of Pol I during DNA replication might be detectable as increases in the bacterial mutation rate. Using a series of defined lacZ reversion alleles in two orientations on the chromosome as markers for mutagenesis, 1.5- to 4-fold increases in mutant frequencies were observed. In general, these increases were largest for lac orientations favouring events during lagging strand DNA replication. Further analysis of these effects in strains affected in other E. coli DNA replication functions indicated that this polAexo mutator effect is best explained by an effect that is additive compared with other error-producing events at the replication fork. No evidence was found that Pol I participates in the polymerase switching between Pol II, III and IV at the fork. Instead, our data suggest that the additional errors produced by polAexo are created during the maturation of Okazaki fragments in the lagging strand.
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Affiliation(s)
- Karolina Makiela-Dzbenska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, Warsaw, Poland
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28
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Janowska B, Komisarski M, Prorok P, Sokołowska B, Kuśmierek J, Janion C, Tudek B. Nucleotide excision repair and recombination are engaged in repair of trans-4-hydroxy-2-nonenal adducts to DNA bases in Escherichia coli. Int J Biol Sci 2009; 5:611-20. [PMID: 19834545 PMCID: PMC2757579 DOI: 10.7150/ijbs.5.611] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Accepted: 09/15/2009] [Indexed: 01/15/2023] Open
Abstract
One of the major products of lipid peroxidation is trans-4-hydroxy-2-nonenal (HNE). HNE forms highly mutagenic and genotoxic adducts to all DNA bases. Using M13 phage lacZ system, we studied the mutagenesis and repair of HNE treated phage DNA in E. coli wild-type or uvrA, recA, and mutL mutants. These studies revealed that: (i) nucleotide excision and recombination, but not mismatch repair, are engaged in repair of HNE adducts when present in phage DNA replicating in E. coli strains; (ii) in the single uvrA mutant, phage survival was drastically decreased while mutation frequency increased, and recombination events constituted 48 % of all mutations; (iii) in the single recA mutant, the survival and mutation frequency of HNE-modified M13 phage was slightly elevated in comparison to that in the wild-type bacteria. The majority of mutations in recA- strain were G:C → T:A transversions, occurring within the sequence which in recA+ strains underwent RecA-mediated recombination, and the entire sequence was deleted; (iv) in the double uvrA recA mutant, phage survival was the same as in the wild-type although the mutation frequency was higher than in the wild-type and recA single mutant, but lower than in the single uvrA mutant. The majority of mutations found in the latter strain were base substitutions, with G:C → A:T transitions prevailing. These transitions could have resulted from high reactivity of HNE with G and C, and induction of SOS-independent mutations.
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Affiliation(s)
- Beata Janowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland
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A novel mutator of Escherichia coli carrying a defect in the dgt gene, encoding a dGTP triphosphohydrolase. J Bacteriol 2008; 190:6931-9. [PMID: 18776019 DOI: 10.1128/jb.00935-08] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A novel mutator locus in Escherichia coli was identified from a collection of random transposon insertion mutants. Several mutators in this collection were found to have an insertion in the dgt gene, encoding a previously characterized dGTP triphosphohydrolase. The mutator activity of the dgt mutants displays an unusual specificity. Among the six possible base pair substitutions in a lacZ reversion system, the G.C-->C.G transversion and A.T-->G.C transition are strongly enhanced (10- to 50-fold), while a modest effect (two- to threefold) is also observed for the G.C-->A.T transition. Interestingly, a two- to threefold reduction in mutant frequency (antimutator effect) is observed for the G.C-->T.A transversion. In the absence of DNA mismatch repair (mutL) some of these effects are reduced or abolished, while other effects remain unchanged. Analysis of these effects, combined with the DNA sequence contexts in which the reversions take place, suggests that alterations of the dGTP pools as well as alterations in the level of some modified dNTP derivatives could affect the fidelity of in vivo DNA replication and, hence, account for the overall mutator effects.
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30
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Role of accessory DNA polymerases in DNA replication in Escherichia coli: analysis of the dnaX36 mutator mutant. J Bacteriol 2007; 190:1730-42. [PMID: 18156258 DOI: 10.1128/jb.01463-07] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The dnaX36(TS) mutant of Escherichia coli confers a distinct mutator phenotype characterized by enhancement of transversion base substitutions and certain (-1) frameshift mutations. Here, we have further investigated the possible mechanism(s) underlying this mutator effect, focusing in particular on the role of the various E. coli DNA polymerases. The dnaX gene encodes the tau subunit of DNA polymerase III (Pol III) holoenzyme, the enzyme responsible for replication of the bacterial chromosome. The dnaX36 defect resides in the C-terminal domain V of tau, essential for interaction of tau with the alpha (polymerase) subunit, suggesting that the mutator phenotype is caused by an impaired or altered alpha-tau interaction. We previously proposed that the mutator activity results from aberrant processing of terminal mismatches created by Pol III insertion errors. The present results, including lack of interaction of dnaX36 with mutM, mutY, and recA defects, support our assumption that dnaX36-mediated mutations originate as errors of replication rather than DNA damage-related events. Second, an important role is described for DNA Pol II and Pol IV in preventing and producing, respectively, the mutations. In the system used, a high fraction of the mutations is dependent on the action of Pol IV in a (dinB) gene dosage-dependent manner. However, an even larger but opposing role is deduced for Pol II, revealing Pol II to be a major editor of Pol III mediated replication errors. Overall, the results provide insight into the interplay of the various DNA polymerases, and of tau subunit, in securing a high fidelity of replication.
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Hardin A, Villalta CF, Doan M, Jabri M, Chockalingham V, White SJ, Fowler RG. A molecular characterization of spontaneous frameshift mutagenesis within the trpA gene of Escherichia coli. DNA Repair (Amst) 2007; 6:177-89. [PMID: 17084112 PMCID: PMC1804121 DOI: 10.1016/j.dnarep.2006.09.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 09/05/2006] [Accepted: 09/25/2006] [Indexed: 10/24/2022]
Abstract
Spontaneous frameshift mutations are an important source of genetic variation in all species and cause a large number of genetic disorders in humans. To enhance our understanding of the molecular mechanisms of frameshift mutagenesis, 583 spontaneous Trp+ revertants of two trpA frameshift alleles in Escherichia coli were isolated and DNA sequenced. In order to measure the contribution of methyl-directed mismatch repair to frameshift production, mutational spectra were constructed for both mismatch repair-proficient and repair-defective strains. The molecular origins of practically all of the frameshifts analyzed could be explained by one of six simple models based upon misalignment of the template or nascent DNA strands with or without misincorporation of primer nucleotides during DNA replication. Most frameshifts occurred within mononucleotide runs as has been shown often in previous studies but the location of the 76 frameshift sites was usually outside of runs. Mismatch repair generally was most effective in preventing the occurrence of frameshifts within runs but there was much variation from site to site. Most frameshift sites outside of runs appear to be refractory to mismatch repair although the small number of occurrences at most of these sites make firm conclusions impossible. There was a dense pattern of reversion sites within the trpA DNA region where reversion events could occur, suggesting that, in general, most DNA sequences are capable of undergoing spontaneous mutational events during replication that can lead to small deletions and insertions. Many of these errors are likely to occur at low frequencies and be tolerated as events too costly to prevent or repair. These studies also revealed an unpredicted flexibility in the primary amino acid sequence of the trpA product, the alpha subunit of tryptophan synthase.
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Affiliation(s)
- Aaron Hardin
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | | | - Michael Doan
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | - Mouna Jabri
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | | | - Steven J. White
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | - Robert G. Fowler
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
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Huen MSY, Li XT, Lu LY, Watt RM, Liu DP, Huang JD. The involvement of replication in single stranded oligonucleotide-mediated gene repair. Nucleic Acids Res 2006; 34:6183-94. [PMID: 17088285 PMCID: PMC1693898 DOI: 10.1093/nar/gkl852] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Targeted gene repair mediated by single-stranded oligonucleotides (SSOs) has great potential for use in functional genomic studies and gene therapy. Genetic changes have been created using this approach in a number of prokaryotic and eukaryotic systems, including mouse embryonic stem cells. However, the underlying mechanisms remain to be fully established. In one of the current models, the ‘annealing-integration’ model, the SSO anneals to its target locus at the replication fork, serving as a primer for subsequent DNA synthesis mediated by the host replication machinery. Using a λ-Red recombination-based system in the bacterium Escherichia coli, we systematically examined several fundamental premises that form the mechanistic basis of this model. Our results provide direct evidence strongly suggesting that SSO-mediated gene repair is mechanistically linked to the process of DNA replication, and most likely involves a replication intermediate. These findings will help guide future experiments involving SSO-mediated gene repair in mammalian and prokaryotic cells, and suggest several mechanisms by which the efficiencies may be reliably and substantially increased.
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Affiliation(s)
- Michael S. Y. Huen
- Department of Biochemistry, The University of Hong Kong3/F Laboratory Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong SAR, China
| | - Xin-tian Li
- Department of Biochemistry, The University of Hong Kong3/F Laboratory Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong SAR, China
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC)Beijing 100005, P.R. China
| | - Lin-Yu Lu
- Department of Biochemistry, The University of Hong Kong3/F Laboratory Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong SAR, China
| | - Rory M. Watt
- Open Laboratory of Chemical Biology, The Institute of Molecular Technology for Drug Discovery and Synthesis, Department of Chemistry, The University of Hong Kong Pokfulam RoadHong Kong SAR, China
| | - De-Pei Liu
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC)Beijing 100005, P.R. China
| | - Jian-Dong Huang
- Department of Biochemistry, The University of Hong Kong3/F Laboratory Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong SAR, China
- To whom correspondence should be addressed. Tel: +852 2819 2810; Fax: +852 2855 1254;
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Pham PT, Zhao W, Schaaper RM. Mutator mutants of Escherichia coli carrying a defect in the DNA polymerase III tau subunit. Mol Microbiol 2006; 59:1149-61. [PMID: 16430690 DOI: 10.1111/j.1365-2958.2005.05011.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To investigate the possible role of accessory subunits of Escherichia coli DNA polymerase III holoenzyme (HE) in determining chromosomal replication fidelity, we have investigated the role of the dnaX gene. This gene encodes both the tau and gamma subunits of HE, which play a central role in the organization and functioning of HE at the replication fork. We find that a classical, temperature-sensitive dnaX allele, dnaX36, displays a pronounced mutator effect, characterized by an unusual specificity: preferential enhancement of transversions and -1 frameshifts. The latter occur predominantly at non-run sequences. The dnaX36 defect does not affect the gamma subunit, but produces a tau subunit carrying a missense substitution (E601K) in its C-terminal domain (domain V) that is involved in interaction with the Pol III alpha subunit. A search for new mutators in the dnaX region of the chromosome yielded six additional dnaX mutators, all carrying a specific tau subunit defect. The new mutators displayed phenotypes similar to dnaX36: strong enhancement of transversions and frameshifts and only weak enhancement for transitions. The combined findings suggest that the tau subunit of HE plays an important role in determining the fidelity of the chromosomal replication, specifically in the avoidance of transversions and frameshift mutations.
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Affiliation(s)
- Phuong T Pham
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
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Pavlov YI, Shcherbakova PV, Rogozin IB. Roles of DNA Polymerases in Replication, Repair, and Recombination in Eukaryotes. INTERNATIONAL REVIEW OF CYTOLOGY 2006; 255:41-132. [PMID: 17178465 DOI: 10.1016/s0074-7696(06)55002-8] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The functioning of the eukaryotic genome depends on efficient and accurate DNA replication and repair. The process of replication is complicated by the ongoing decomposition of DNA and damage of the genome by endogenous and exogenous factors. DNA damage can alter base coding potential resulting in mutations, or block DNA replication, which can lead to double-strand breaks (DSB) and to subsequent chromosome loss. Replication is coordinated with DNA repair systems that operate in cells to remove or tolerate DNA lesions. DNA polymerases can serve as sensors in the cell cycle checkpoint pathways that delay cell division until damaged DNA is repaired and replication is completed. Eukaryotic DNA template-dependent DNA polymerases have different properties adapted to perform an amazingly wide spectrum of DNA transactions. In this review, we discuss the structure, the mechanism, and the evolutionary relationships of DNA polymerases and their possible functions in the replication of intact and damaged chromosomes, DNA damage repair, and recombination.
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Affiliation(s)
- Youri I Pavlov
- Eppley Institute for Research in Cancer and Allied Diseases, Departments of Biochemistry and Molecular Biology, and Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805, USA
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Kuban W, Banach-Orlowska M, Bialoskorska M, Lipowska A, Schaaper RM, Jonczyk P, Fijalkowska IJ. Mutator phenotype resulting from DNA polymerase IV overproduction in Escherichia coli: preferential mutagenesis on the lagging strand. J Bacteriol 2005; 187:6862-6. [PMID: 16166552 PMCID: PMC1251572 DOI: 10.1128/jb.187.19.6862-6866.2005] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We investigated the mutator effect resulting from overproduction of Escherichia coli DNA polymerase IV. Using lac mutational targets in the two possible orientations on the chromosome, we observed preferential mutagenesis during lagging strand synthesis. The mutator activity likely results from extension of mismatches produced by polymerase III holoenzyme.
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Affiliation(s)
- Wojciech Kuban
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, 02106 Warsaw, Poland
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Banach-Orlowska M, Fijalkowska IJ, Schaaper RM, Jonczyk P. DNA polymerase II as a fidelity factor in chromosomal DNA synthesis in Escherichia coli. Mol Microbiol 2005; 58:61-70. [PMID: 16164549 DOI: 10.1111/j.1365-2958.2005.04805.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Escherichia coli DNA polymerase III holoenzyme (HE) is the main replicase responsible for replication of the bacterial chromosome. E. coli contains four additional polymerases, and it is a relevant question whether these might also contribute to chromosomal replication and its fidelity. Here, we have investigated the role of DNA polymerase II (Pol II) (polB gene product). Mismatch repair-defective strains containing the polBex1 allele--encoding a polymerase-proficient but exonucleolytically defective Pol II--displayed a mutator activity for four different chromosomal lac mutational markers. The mutator effect was dependent on the chromosomal orientation of the lacZ gene. The results indicate that Pol II plays a role in chromosomal replication and that its role is not equal in leading- versus lagging-strand replication. In particular, the role of Pol II appeared larger in the lagging strand. When combined with dnaQ or dnaE mutator alleles, polBex1 showed strong, near multiplicative effects. The results fit a model in which Pol II acts as proofreader for HE-produced misinsertion errors. A second role of Pol II is to protect mismatched 3' termini against the mutagenic action of polymerase IV (dinB product). Overall, Pol II may be considered a main player in the polymerase trafficking at the replication fork.
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Affiliation(s)
- Magdalena Banach-Orlowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, Warsaw, Poland
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Pavlov YI, Maki S, Maki H, Kunkel TA. Evidence for interplay among yeast replicative DNA polymerases alpha, delta and epsilon from studies of exonuclease and polymerase active site mutations. BMC Biol 2004; 2:11. [PMID: 15163346 PMCID: PMC434536 DOI: 10.1186/1741-7007-2-11] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2004] [Accepted: 05/26/2004] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND DNA polymerase epsilon (Pol epsilon) is essential for S-phase replication, DNA damage repair and checkpoint control in yeast. A pol2-Y831A mutation leading to a tyrosine to alanine change in the Pol epsilon active site does not cause growth defects and confers a mutator phenotype that is normally subtle but strong in a mismatch repair-deficient strain. Here we investigate the mechanism responsible for the mutator effect. RESULTS Purified four-subunit Y831A Pol epsilon turns over more deoxynucleoside triphosphates to deoxynucleoside monophosphates than does wild-type Pol epsilon, suggesting altered coordination between the polymerase and exonuclease active sites. The pol2-Y831A mutation suppresses the mutator effect of the pol2-4 mutation in the exonuclease active site that abolishes proofreading by Pol epsilon, as measured in haploid strain with the pol2-Y831A,4 double mutation. Analysis of mutation rates in diploid strains reveals that the pol2-Y831A allele is recessive to pol2-4. In addition, the mutation rates of strains with the pol2-4 mutation in combination with active site mutator mutations in Pol delta and Pol alpha suggest that Pol epsilon may proofread certain errors made by Pol alpha and Pol delta during replication in vivo. CONCLUSIONS Our data suggest that Y831A replacement in Pol epsilon reduces replication fidelity and its participation in chromosomal replication, but without eliminating an additional function that is essential for viability. This suggests that other polymerases can substitute for certain functions of polymerase epsilon.
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Affiliation(s)
- Youri I Pavlov
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institute of Health, DHHS, Research Triangle Park, NC 27709, USA
- Eppley Institute for Research in Cancer and Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - Satoko Maki
- Laboratory of Microbial Molecular Genetics, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Nara 630-01, Japan
| | - Hisaji Maki
- Laboratory of Microbial Molecular Genetics, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Nara 630-01, Japan
| | - Thomas A Kunkel
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institute of Health, DHHS, Research Triangle Park, NC 27709, USA
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences National Institute of Health, DHHS, Research Triangle Park, NC 27709, USA
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Abstract
Many mutator genes have been characterized in E. coli, but the realization that mutA, the most recent mutator pathway described, encodes for a missense suppressor glycine tRNA caused a real surprise. The connection between expression of mutA and a 10 times increase in the spontaneous mutation rate is not readily explainable. The first attempt to describe the mechanism of action suggested a direct mistranslation of one subunit of polymerase III (PolIII) and the ideal candidate was the epsilon subunit carrying the 3'-->5' exonuclease activity. This subunit increases PolIII accuracy about 100 times. However, such direct mistranslation of epsilon was later ruled out when it became clear that all mutA cells express an error-prone form of PolIII. This result could not be reconciled with the very low level of mistranslation (1%) caused by mutA. But there is no need to invoke amino acid misincorporation in epsilon to destroy its activity. On the contrary, I suggest a new way to regulate epsilon amount, based on the reinterpretation of the mutA pathway through the new and puzzling observation that several tRNAs (including mutA which encodes for a glycine missense suppressor tRNA) are complementary to the 5' end of dnaQ mRNA. Accordingly, I propose that uncharged tRNAs can act as antisense RNAs, decreasing translation of dnaQ and possibly other genes. This could represent a new regulatory function for tRNAs and of course gives a direct and unrecognized link between starvation and mutation rate.
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Deb DK, Dahiya P, Srivastava KK, Srivastava R, Srivastava BS. Selective identification of new therapeutic targets of Mycobacterium tuberculosis by IVIAT approach. Tuberculosis (Edinb) 2003; 82:175-82. [PMID: 12464489 DOI: 10.1054/tube.2002.0337] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The in vivo induced antigen technology (IVIAT)(1) has been used for the identification of open reading frames (ORFs) which could be possible therapeutic targets. A recombinant lambdagt11:: Mycobacterium tuberculosis H37Rv expression library was screened with pooled TB patient sera preabsorbed with in vitro grown M. tuberculosis H37Rv. Preabsorption of pooled TB patient sera allowed identification of antigens specifically expressed or upregulated during infection and growth in vivo. Six ORFs were identified, of which four (rv0287, rv2402, rv3878 and rv1045) were of hypothetical functions. Rv0287 is a probable regulatory protein. Rv3878 is present uniquely in M. tuberculosis H37Rv and is a part of RDI deletion region of M. bovis BCG, which includes esat 6 region. This could be exploited as a tool for diagnosis. Two ORFs were assigned function solely on the basis of homology, dnaQ (rv3711c) and lpdA (rv3303c). dnaQ codes for the epsilon subunit of DNA polymerase III, which is responsible for the proofreading activity of the complex. lpdA codes for dihydrolipoamide dehydrogenase, which is a part of many multienzyme complexes such as pyruvate dehydrogenase, keto-acid dehydrogenase and alpha-ketoglutarate dehydrogenase. These two enzymes appear to be potential targets for drug development.
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MESH Headings
- Antigens, Bacterial/genetics
- Antigens, Bacterial/immunology
- Blotting, Western
- DNA, Bacterial/genetics
- DNA, Bacterial/immunology
- DNA, Recombinant/genetics
- DNA, Recombinant/immunology
- Electrophoresis, Polyacrylamide Gel
- Gene Expression Regulation, Bacterial/genetics
- Gene Expression Regulation, Bacterial/immunology
- Genomic Library
- Humans
- Mycobacteriophages/genetics
- Mycobacteriophages/immunology
- Mycobacterium bovis/genetics
- Mycobacterium bovis/immunology
- Mycobacterium tuberculosis/genetics
- Mycobacterium tuberculosis/immunology
- Open Reading Frames/genetics
- Open Reading Frames/immunology
- Tuberculosis, Pulmonary/drug therapy
- Tuberculosis, Pulmonary/immunology
- beta-Galactosidase/genetics
- beta-Galactosidase/immunology
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Affiliation(s)
- D K Deb
- Microbiology Division, Central Drug Research Institute, Lucknow 226 001, India
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Gawel D, Maliszewska-Tkaczyk M, Jonczyk P, Schaaper RM, Fijalkowska IJ. Lack of strand bias in UV-induced mutagenesis in Escherichia coli. J Bacteriol 2002; 184:4449-54. [PMID: 12142415 PMCID: PMC135265 DOI: 10.1128/jb.184.16.4449-4454.2002] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
We have investigated whether UV-induced mutations are created with equal efficiency on the leading and lagging strands of DNA replication. We employed an assay system that permits measurement of mutagenesis in the lacZ gene in pairs of near-identical strains. Within each pair, the strains differ only in the orientation of the lacZ gene with respect to the origin of DNA replication. Depending on this orientation, any lacZ target sequence will be replicated in one orientation as a leading strand and as a lagging strand in the other orientation. In contrast to previous results obtained for mutations resulting from spontaneous replication errors or mutations resulting from the spontaneous SOS mutator effect, measurements of UV-induced mutagenesis in uvrA strains fail to show significant differences between the two target orientations. These data suggest that SOS-mediated mutagenic translesion synthesis on the Escherichia coli chromosome may occur with equal or similar probability on leading and lagging strands.
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Affiliation(s)
- Damian Gawel
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02 106 Warsaw, Poland
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Gawel D, Jonczyk P, Bialoskorska M, Schaaper RM, Fijalkowska IJ. Asymmetry of frameshift mutagenesis during leading and lagging-strand replication in Escherichia coli. Mutat Res 2002; 501:129-36. [PMID: 11934444 DOI: 10.1016/s0027-5107(02)00020-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Mutations in DNA, including frameshifts, may arise during DNA replication as a result of mistakes made by the DNA polymerase in copying the DNA template strands. In our efforts to better understand the factors that contribute to the accuracy of DNA replication, we have investigated whether frameshift mutations on the Escherichia coli chromosome occur differentially within the leading and lagging-strands of replication. The experimental system involves measurement of the reversion frequency for several defined lac frameshift alleles in pairs of strains in which the lac target is oriented in the two possible directions relative to the origin of chromosomal replication. Within these pairs any defined lac sequence will be subject to leading-strand replication in one orientation and to lagging-strand replication in the other. Fidelity differences between the two modes of replication can be observed as a differential lac reversion between the two strains. Our results, obtained with a series of lac alleles in a mismatch-repair-defective background, indicate that for at least some of the alleles there is indeed a difference in the fidelity of replication between the two modes of replication.
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Affiliation(s)
- Damian Gawel
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, Warsaw, Poland
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42
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Vandewiele D, Fernández de Henestrosa AR, Timms AR, Bridges BA, Woodgate R. Sequence analysis and phenotypes of five temperature sensitive mutator alleles of dnaE, encoding modified alpha-catalytic subunits of Escherichia coli DNA polymerase III holoenzyme. Mutat Res 2002; 499:85-95. [PMID: 11804607 DOI: 10.1016/s0027-5107(01)00268-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In the 1970s, several thermosensitive alleles of dnaE (encoding the alpha-catalytic subunit of pol III) were isolated. Genetic characterization of these dnaE mutants revealed that some are mutator alleles at permissive temperature. We have determined the nucleotide changes of five such temperature sensitive mutator alleles (dnaE9, dnaE74, dnaE486, dnaE511, and dnaE1026) and find that most are single missense mutations. The exception is dnaE1026 which is a compound allele consisting of multiple missense mutations. When the previously characterized mutator alleles were moved into a lexA51(Def) recA730 strain, dnaE486, dnaE1026 and dnaE74 conferred a modest approximately two-six-fold increase in spontaneous mutagenesis when grown at the permissive temperature of 28 degrees C, while dnaE9 and dnaE511 actually resulted in a slight decrease in spontaneous mutagenesis. In isogenic DeltaumuDC derivatives, the level of spontaneous mutagenesis dropped significantly, although in each case, the overall mutator effect conferred by the dnaE allele was relatively larger, with all five dnaE alleles conferring an increased spontaneous mutation rate approximately 5-22-fold over the isogenic dnaE+ DeltaumuDC strain. Interestingly, the temperature sensitivity conferred by each allele varied considerably in the lexA51(Def) recA730 background and in many cases, this phenotype was dependent upon the presence of functional pol V (UmuD'2C). Our data suggest that pol V can compete effectively with the impaired alpha-subunit for a 3' primer terminus and as a result, a large proportion of the phenotypic effects observed with strains carrying missense temperature sensitive mutations in dnaE can, in fact, be attributed to the actions of pol V rather than pol III.
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Affiliation(s)
- Dominique Vandewiele
- Section on DNA Replication, Repair and Mutagenesis, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2725, USA
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Lochowska A, Iwanicka-Nowicka R, Plochocka D, Hryniewicz MM. Functional dissection of the LysR-type CysB transcriptional regulator. Regions important for DNA binding, inducer response, oligomerization, and positive control. J Biol Chem 2001; 276:2098-107. [PMID: 11038360 DOI: 10.1074/jbc.m007192200] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CysB is a tetrameric LysR-type transcriptional regulator that acts as an activator of cys regulon genes and as an autorepressor. Positive control of cys genes requires the presence of the inducer N-acetylserine. Following random and site-directed mutagenesis of the cysB gene, 20 CysB variants were isolated. Six single amino acid substitutions within the N terminus of CysB abolished the DNA-binding ability of the protein. Seven mutations in the central region of CysB affected its response to the inducer. Four of these CysB mutants retained repressing activity, but lost their activating function in vivo. Their DNA binding characteristics were consistent with an inability to respond to acetylserine by a qualitative change in the DNA-protein interaction. Three of the single residue substitutions resulted in constitutive activity of CysB. The electrophoretic mobility of the complex formed by one of the CysBc variants with the cysP promoter suggested a dimeric state of this protein. Characteristics of six truncated CysB variants lacking 5-30 C-terminal residues indicated the involvement of the C terminus in the DNA binding, oligomerization, and stability of CysB. The single substitution Y27G resulted in the CysBpc variant, able to bind DNA and to respond to the inducer by a qualitative change in the DNA-protein complex, but defective in the positive control of the cysP promoter.
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Affiliation(s)
- A Lochowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02-106 Warsaw, Poland
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44
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Strauss BS, Roberts R, Francis L, Pouryazdanparast P. Role of the dinB gene product in spontaneous mutation in Escherichia coli with an impaired replicative polymerase. J Bacteriol 2000; 182:6742-50. [PMID: 11073920 PMCID: PMC111418 DOI: 10.1128/jb.182.23.6742-6750.2000] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2000] [Accepted: 09/13/2000] [Indexed: 11/20/2022] Open
Abstract
We isolated several new mutator mutations of the Escherichia coli replicative polymerase dnaE subunit alpha and used them and a previously reported dnaE mutation to study spontaneous frameshift and base substitution mutations. Two of these dnaE strains produce many more mutants when grown on rich (Luria-Bertani) than on minimal medium. A differential effect of the medium was not observed when these dnaE mutations were combined with a mismatch repair mutation. The selection scheme for the dnaE mutations required that they be able to complement a temperature-sensitive strain. However, the ability to complement is not related to the mutator effect for at least one of the mutants. Comparison of the mutation rates for frameshift and base substitution mutations in mutS and dnaE mutS strains suggests that the mismatch repair proteins respond differently to the two types of change. Deletion of dinB from both chromosome and plasmid resulted in a four- to fivefold decrease in the rate of frameshift and base substitution mutations in a dnaE mutS double mutant background. This reduction indicates that most mistakes in replication occur as a result of the action of the auxiliary rather than the replicative polymerase in this dnaE mutant. Deletion of dinB from strains carrying a wild-type dnaE had a measurable effect, suggesting that a fraction of spontaneous mutations occur as a result of dinB polymerase action even in cells with a normal replicative polymerase.
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Affiliation(s)
- B S Strauss
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA.
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Maliszewska-Tkaczyk M, Jonczyk P, Bialoskorska M, Schaaper RM, Fijalkowska IJ. SOS mutator activity: unequal mutagenesis on leading and lagging strands. Proc Natl Acad Sci U S A 2000; 97:12678-83. [PMID: 11050167 PMCID: PMC18823 DOI: 10.1073/pnas.220424697] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A major pathway of mutagenesis in Escherichia coli is mediated by the inducible SOS response. Current models of SOS mutagenesis invoke the interaction of RecA and UmuD'(2)C proteins with a stalled DNA replication complex at sites of DNA lesions or poorly extendable terminal mismatches, resulting in an (error-prone) continuation of DNA synthesis. The precise mechanisms of SOS-mediated lesion bypass or mismatch extension are not known. Here, we have studied mutagenesis on the E. coli chromosome in recA730 strains. In recA730 strains, the SOS system is expressed constitutively, resulting in a spontaneous mutator effect (SOS mutator) because of reduced replication fidelity. We investigated whether during SOS mutator activity replication fidelity might be altered differentially in the leading and lagging strand of replication. Pairs of recA730 strains were constructed differing in the orientation of the lac operon relative to the origin of replication. The strains were also mismatch-repair defective (mutL) to facilitate scoring of replication errors. Within each pair, a given lac sequence is replicated by the leading-strand machinery in one orientation and by the lagging-strand machinery in the other orientation. Measurements of defined lac mutant frequencies in such pairs revealed large differences between the two orientations. Furthermore, in all cases, the frequency bias was the opposite of that seen in normal cells. We suggest that, for the lacZ target used in this study, SOS mutator activity operates with very different efficiency in the two strands. Specifically, the lagging strand of replication appears most susceptible to the SOS mutator effect.
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Affiliation(s)
- M Maliszewska-Tkaczyk
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, 02-106 Warsaw, Poland
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Reddy M, Gowrishankar J. Characterization of the uup locus and its role in transposon excisions and tandem repeat deletions in Escherichia coli. J Bacteriol 2000; 182:1978-86. [PMID: 10715006 PMCID: PMC101901 DOI: 10.1128/jb.182.7.1978-1986.2000] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Null mutations in the Escherichia coli uup locus (at 21.8 min) serve to increase the frequency of RecA-independent precise excision of transposable elements such as Tn10 and to reduce the plaque size of bacteriophage Mu (Uup(-) phenotype). By the combined approaches of physical mapping of the mutations, complementation analyses, and protein overexpression from cloned gene fragments, we have demonstrated in this study that the Uup(-) phenotype is the consequence of the absence of expression of the downstream gene (uup) of a two-gene operon, caused either directly by insertions in uup or indirectly by the polar effect of insertions in the upstream gene (ycbY). The promoter for uup was mapped upstream of ycbY by primer extension analysis on cellular RNA, and assays of reporter gene expression indicated that it is a moderately active, constitutive promoter. The uup mutations were also shown to increase, in a RecA-independent manner, the frequencies of nearly precise excision of Tn10 derivatives and of the deletion of one copy of a chromosomal tandem repeat, suggesting the existence of a shared step or intermediate in the pathways of these latter events and that of precise excision. Finally, we found that mutations that increase the frequency of precise excision of Tn10 are divisible into two categories, depending upon whether they did (uup, ssb, polA, and topA) or did not (mutHLS, dam, and uvrD) also increase precise excision frequency of the mini-Tn10 derivatives. It is suggested that the differential response of mini-Tn10 and Tn10 to the second category of mutations is related to the presence, respectively, of perfect and of imperfect terminal inverted repeats in them.
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Affiliation(s)
- M Reddy
- Centre for Cellular and Molecular Biology, Hyderabad 500 007, India
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Tran HT, Degtyareva NP, Gordenin DA, Resnick MA. Genetic factors affecting the impact of DNA polymerase delta proofreading activity on mutation avoidance in yeast. Genetics 1999; 152:47-59. [PMID: 10224242 PMCID: PMC1460598 DOI: 10.1093/genetics/152.1.47] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Base selectivity, proofreading, and postreplication mismatch repair are important for replication fidelity. Because proofreading plays an important role in error correction, we have investigated factors that influence its impact in the yeast Saccharomyces cerevisiae. We have utilized a sensitive mutation detection system based on homonucleotide runs of 4 to 14 bases to examine the impact of DNA polymerase delta proofreading on mutation avoidance. The contribution of DNA polymerase delta proofreading on error avoidance was found to be similar to that of DNA polymerase epsilon proofreading in short homonucleotide runs (A4 and A5) but much greater than the contribution of DNA polymerase epsilon proofreading in longer runs. We have identified an intraprotein interaction affecting mutation prevention that results from mutations in the replication and the proofreading regions, resulting in an antimutator phenotype relative to a proofreading defect. Finally, a diploid strain with a defect in DNA polymerase delta proofreading exhibits a higher mutation rate than a haploid strain. We suggest that in the diploid population of proofreading defective cells there exists a transiently hypermutable fraction that would be inviable if cells were haploids.
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Affiliation(s)
- H T Tran
- Chromosome Stability Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
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Vandewiele D, Borden A, O'Grady PI, Woodgate R, Lawrence CW. Efficient translesion replication in the absence of Escherichia coli Umu proteins and 3'-5' exonuclease proofreading function. Proc Natl Acad Sci U S A 1998; 95:15519-24. [PMID: 9861001 PMCID: PMC28075 DOI: 10.1073/pnas.95.26.15519] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Translesion replication (TR) past a cyclobutane pyrimidine dimer in Escherichia coli normally requires the UmuD'2C complex, RecA protein, and DNA polymerase III holoenzyme (pol III). However, we find that efficient TR can occur in the absence of the Umu proteins if the 3'-5' exonuclease proofreading activity of the pol III epsilon-subunit also is disabled. TR was measured in isogenic uvrA6 DeltaumuDC strains carrying the dominant negative dnaQ allele, mutD5, or DeltadnaQ spq-2 mutations by transfecting them with single-stranded M13-based vectors containing a specifically located cis-syn T-T dimer. As expected, little TR was observed in the DeltaumuDC dnaQ+ strain. Surprisingly, 26% TR occurred in UV-irradiated DeltaumuDC mutD5 cells, one-half the frequency found in a uvrA6 umuDC+mutD5 strain. lexA3 (Ind-) derivatives of the strains showed that this TR was contingent on two inducible functions, one LexA-dependent, responsible for approximately 70% of the TR, and another LexA-independent, responsible for the remaining approximately 30%. Curiously, the DeltaumuDC DeltadnaQ spq-2 strain exhibited only the LexA-independent level of TR. The cause of this result appears to be the spq-2 allele, a dnaE mutation required for viability in DeltadnaQ strains, since introduction of spq-2 into the DeltaumuDC mutD5 strain also reduces the frequency of TR to the LexA-independent level. The molecular mechanism responsible for the LexA-independent TR is unknown but may be related to the UVM phenomenon [Palejwala, V. A., Wang, G. E., Murphy, H. S. & Humayun, M. Z. (1995) J. Bacteriol. 177, 6041-6048]. LexA-dependent TR does not result from the induction of pol II, since TR in the DeltaumuDC mutD5 strain is unchanged by introduction of a DeltapolB mutation.
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Affiliation(s)
- D Vandewiele
- Section on DNA Replication, Repair and Mutagenesis, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2725, USA
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Abstract
This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.
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Affiliation(s)
- M K Berlyn
- Department of Biology and School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06520-8104, USA.
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Fijalkowska IJ, Jonczyk P, Tkaczyk MM, Bialoskorska M, Schaaper RM. Unequal fidelity of leading strand and lagging strand DNA replication on the Escherichia coli chromosome. Proc Natl Acad Sci U S A 1998; 95:10020-5. [PMID: 9707593 PMCID: PMC21454 DOI: 10.1073/pnas.95.17.10020] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have investigated the question whether during chromosomal DNA replication in Escherichia coli the two DNA strands may be replicated with differential accuracy. This possibility of differential replication fidelity arises from the distinct modes of replication in the two strands, one strand (the leading strand) being synthesized continuously, the other (the lagging strand) discontinuously in the form of short Okazaki fragments. We have constructed a series of lacZ strains in which the lac operon is inserted into the bacterial chromosome in the two possible orientations with regard to the chromosomal replication origin oriC. Measurement of lac reversion frequencies for the two orientations, under conditions in which mutations reflect replication errors, revealed distinct differences in mutability between the two orientations. As gene inversion causes a switching of leading and lagging strands, these findings indicate that leading and lagging strand replication have differential fidelity. Analysis of the possible mispairs underlying each specific base pair substitution suggests that the lagging strand replication on the E. coli chromosome may be more accurate than leading strand replication.
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Affiliation(s)
- I J Fijalkowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02 106 Warsaw, Pawinskiego 5A, Poland.
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