1
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Sugawara N, Towne MJ, Lovett ST, Haber JE. Spontaneous and double-strand break repair-associated quasipalindrome and frameshift mutagenesis in budding yeast: role of mismatch repair. Genetics 2024; 227:iyae068. [PMID: 38691577 DOI: 10.1093/genetics/iyae068] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 08/09/2023] [Accepted: 03/06/2024] [Indexed: 05/03/2024] Open
Abstract
Although gene conversion (GC) in Saccharomyces cerevisiae is the most error-free way to repair double-strand breaks (DSBs), the mutation rate during homologous recombination is 1,000 times greater than during replication. Many mutations involve dissociating a partially copied strand from its repair template and re-aligning with the same or another template, leading to -1 frameshifts in homonucleotide runs, quasipalindrome (QP)-associated mutations and microhomology-mediated interchromosomal template switches. We studied GC induced by HO endonuclease cleavage at MATα, repaired by an HMR::KI-URA3 donor. We inserted into HMR::KI-URA3 an 18-bp inverted repeat where one arm had a 4-bp insertion. Most GCs yield MAT::KI-ura3::QP + 4 (Ura-) outcomes, but template-switching produces Ura+ colonies, losing the 4-bp insertion. If the QP arm without the insertion is first encountered by repair DNA polymerase and is then (mis)used as a template, the palindrome is perfected. When the QP + 4 arm is encountered first, Ura+ derivatives only occur after second-end capture and second-strand synthesis. QP + 4 mutations are suppressed by mismatch repair (MMR) proteins Msh2, Msh3, and Mlh1, but not Msh6. Deleting Rdh54 significantly reduces QP mutations only when events creating Ura+ occur in the context of a D-loop but not during second-strand synthesis. A similar bias is found with a proofreading-defective DNA polymerase mutation (poI3-01). DSB-induced mutations differed in several genetic requirements from spontaneous events. We also created a + 1 frameshift in the donor, expanding a run of 4 Cs to 5 Cs. Again, Ura+ recombinants markedly increased by disabling MMR, suggesting that MMR acts during GC but favors the unbroken, template strand.
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Affiliation(s)
- Neal Sugawara
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center MS029, Brandeis University, Waltham, MA 02454-9110, USA
| | - Mason J Towne
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center MS029, Brandeis University, Waltham, MA 02454-9110, USA
| | - Susan T Lovett
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center MS029, Brandeis University, Waltham, MA 02454-9110, USA
| | - James E Haber
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center MS029, Brandeis University, Waltham, MA 02454-9110, USA
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2
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Löytynoja A. Thousands of human mutation clusters are explained by short-range template switching. Genome Res 2022; 32:1437-1447. [PMID: 35760560 PMCID: PMC9435742 DOI: 10.1101/gr.276478.121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Accepted: 06/21/2022] [Indexed: 02/03/2023]
Abstract
Variation within human genomes is unevenly distributed, and variants show spatial clustering. DNA replication-related template switching is a poorly known mutational mechanism capable of causing major chromosomal rearrangements as well as creating short inverted sequence copies that appear as local mutation clusters in sequence comparisons. In this study, haplotype-resolved genome assemblies representing 25 human populations and multinucleotide variants aggregated from 140,000 human sequencing experiments were reanalyzed. Local template switching could explain thousands of complex mutation clusters across the human genome, the loci segregating within and between populations. During the study, computational tools were developed for identification of template switch events using both short-read sequencing data and genotype data, and for genotyping candidate loci using short-read data. The characteristics of template-switch mutations complicate their detection, and widely used analysis pipelines for short-read sequencing data, normally capable of identifying single nucleotide changes, were found to miss template-switch mutations of tens of base pairs, potentially invalidating medical genetic studies searching for a causative allele behind genetic diseases. Combined with the massive sequencing data now available for humans, the novel tools described here enable building catalogs of affected loci and studying the cellular mechanisms behind template switching in both healthy organisms and disease.
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Affiliation(s)
- Ari Löytynoja
- Institute of Biotechnology, University of Helsinki, FI-00014 Helsinki, Finland
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3
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Template switching in DNA replication can create and maintain RNA hairpins. Proc Natl Acad Sci U S A 2022; 119:2107005119. [PMID: 35046021 PMCID: PMC8794818 DOI: 10.1073/pnas.2107005119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/14/2021] [Indexed: 11/18/2022] Open
Abstract
The evolutionary origin of RNA stem structures and the preservation of their base pairing under a spontaneous and random mutation process have puzzled theoretical evolutionary biologists. DNA replication-related template switching is a mutation mechanism that creates reverse-complement copies of sequence regions within a genome by replicating briefly along either the complementary or nascent DNA strand. Depending on the relative positions and context of the four switch points, this process may produce a reverse-complement repeat capable of forming the stem of a perfect DNA hairpin or fix the base pairing of an existing stem. Template switching is typically thought to trigger large structural changes, and its possible role in the origin and evolution of RNA genes has not been studied. Here, we show that the reconstructed ancestral histories of RNA genes contain mutation patterns consistent with the DNA replication-related template switching. In addition to multibase compensatory mutations, the mechanism can explain complex sequence changes, although mutations breaking the structure rarely get fixed in evolution. Our results suggest a solution for the long-standing dilemma of RNA gene evolution and demonstrate how template switching can both create perfect stems with a single mutation event and help maintaining the stem structure over time. Interestingly, template switching also provides an elegant explanation for the asymmetric base pair frequencies within RNA stems.
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4
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Protein innovation through template switching in the Saccharomyces cerevisiae lineage. Sci Rep 2021; 11:22558. [PMID: 34799587 PMCID: PMC8604942 DOI: 10.1038/s41598-021-01736-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Accepted: 10/27/2021] [Indexed: 11/08/2022] Open
Abstract
DNA polymerase template switching between short, non-identical inverted repeats (IRs) is a genetic mechanism that leads to the homogenization of IR arms and to IR spacer inversion, which cause multinucleotide mutations (MNMs). It is unknown if and how template switching affects gene evolution. In this study, we performed a phylogenetic analysis to determine the effect of template switching between IR arms on coding DNA of Saccharomyces cerevisiae. To achieve this, perfect IRs that co-occurred with MNMs between a strain and its parental node were identified in S. cerevisiae strains. We determined that template switching introduced MNMs into 39 protein-coding genes through S. cerevisiae evolution, resulting in both arm homogenization and inversion of the IR spacer. These events in turn resulted in nonsynonymous substitutions and up to five neighboring amino acid replacements in a single gene. The study demonstrates that template switching is a powerful generator of multiple substitutions within codons. Additionally, some template switching events occurred more than once during S. cerevisiae evolution. Our findings suggest that template switching constitutes a general mutagenic mechanism that results in both nonsynonymous substitutions and parallel evolution, which are traditionally considered as evidence for positive selection, without the need for adaptive explanations.
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5
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Genetic Analysis of DinG Family Helicase YoaA and Its Interaction with Replication Clamp Loader Protein HolC in Escherichia coli. J Bacteriol 2021; 203:e0022821. [PMID: 34181484 PMCID: PMC8378479 DOI: 10.1128/jb.00228-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The XP-D/DinG family of DNA helicases contributes to genomic stability in all three domains of life. Here, we investigate the role of one of these proteins, YoaA, of Escherichia coli. In E. coli, YoaA aids in tolerance to the nucleoside azidothymidine (AZT), a DNA replication inhibitor, and physically interacts with a subunit of the DNA polymerase III holoenzyme, HolC. We map the residues of YoaA required for HolC interaction to its C terminus by yeast two-hybrid analysis. We propose that this interaction competes with HolC’s interaction with HolD and the rest of the replisome; YoaA indeed inhibits growth when overexpressed, dependent on this interaction region. By gene fusions, we show that YoaA is repressed by LexA and induced in response to DNA damage as part of the SOS response. Induction of YoaA by AZT is biphasic, with an immediate response after treatment and a slower response that peaks in the late log phase of growth. This growth-phase-dependent induction by AZT is not blocked by lexA3 (Ind−), which normally negates its self-cleavage, implying another means to induce the DNA damage response that responds to the nutritional state of the cell. We propose that YoaA helicase activity increases access to the 3′ nascent strand during replication; consistent with this, YoaA appears to aid in the removal of potential A-to-T transversion mutations in ndk mutants, which are prone to nucleotide misincorporation. We provide evidence that YoaA and its paralog DinG may also initiate template switching that leads to deletions between tandem repeats in DNA. IMPORTANCE Maintaining genomic stability is crucial for all living organisms. Replication of DNA frequently encounters barriers that must be removed to complete genome duplication. Balancing DNA synthesis with its repair is critical and not entirely understood at a mechanistic level. The YoaA protein, studied here, is required for certain types of DNA repair and interacts in an alternative manner with proteins that catalyze DNA replication. YoaA is part of the well-studied LexA-regulated response to DNA damage, the SOS response. We describe an unusual feature of its regulation that promotes induction after DNA damage as the culture begins to experience starvation. Replication fork repair integrates both DNA damage and nutritional signals. We also show that YoaA affects genomic stability.
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6
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Klaric JA, Glass DJ, Perr EL, Reuven AD, Towne MJ, Lovett ST. DNA damage-signaling, homologous recombination and genetic mutation induced by 5-azacytidine and DNA-protein crosslinks in Escherichia coli. Mutat Res 2021; 822:111742. [PMID: 33743507 DOI: 10.1016/j.mrfmmm.2021.111742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 02/01/2021] [Accepted: 03/08/2021] [Indexed: 11/29/2022]
Abstract
Covalent linkage between DNA and proteins produces highly toxic lesions and can be caused by commonly used chemotherapeutic agents, by internal and external chemicals and by radiation. In this study, using Escherichia coli, we investigate the consequences of 5-azacytidine (5-azaC), which traps covalent complexes between itself and the Dcm cytosine methyltransferase protein. DNA protein crosslink-dependent effects can be ascertained by effects that arise in wild-type but not in dcmΔ strains. We find that 5-azaC induces the bacterial DNA damage response and stimulates homologous recombination, a component of which is Dcm-dependent. Template-switching at an imperfect inverted repeat ("quasipalindrome", QP) is strongly enhanced by 5-azaC and this enhancement was entirely Dcm-dependent and independent of double-strand break repair. The SOS response helps ameliorate the mutagenic effect of 5-azaC but this is not a result of SOS-induced DNA polymerases since their induction, especially PolIV, seems to stimulate QP-associated mutagenesis. Cell division regulator SulA was also required for recovery of QP mutants induced by 5-azaC. In the absence of Lon protease, Dcm-dependent QP-mutagenesis is strongly elevated, suggesting it may play a role in DPC tolerance. Deletions at short tandem repeats, which occur likewise by a replication template-switch, are elevated, but only modestly, by 5-azaC. We see evidence for Dcm-dependent and-independent killing by 5-azaC in sensitive mutants, such as recA, recB, and lon; homologous recombination and deletion mutations are also stimulated in part by a Dcm-independent effect of 5-azaC. Whether this occurs by a different protein/DNA crosslink or by an alternative form of DNA damage is unknown.
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Affiliation(s)
- Julie A Klaric
- Department of Biology and Rosentiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, 02454-9110, United States
| | - David J Glass
- Department of Biology and Rosentiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, 02454-9110, United States
| | - Eli L Perr
- Department of Biology and Rosentiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, 02454-9110, United States
| | - Arianna D Reuven
- Department of Biology and Rosentiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, 02454-9110, United States
| | - Mason J Towne
- Department of Biology and Rosentiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, 02454-9110, United States
| | - Susan T Lovett
- Department of Biology and Rosentiel Basic Medical Sciences Research Center Brandeis University, Waltham, MA, 02454-9110, United States.
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7
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Gomez K, Bertram J, Masel J. Mutation bias can shape adaptation in large asexual populations experiencing clonal interference. Proc Biol Sci 2020; 287:20201503. [PMID: 33081612 DOI: 10.1098/rspb.2020.1503] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The extended evolutionary synthesis invokes a role for development in shaping adaptive evolution, which in population genetics terms corresponds to mutation-biased adaptation. Critics have claimed that clonal interference makes mutation-biased adaptation rare. We consider the behaviour of two simultaneously adapting traits, one with larger mutation rate U, the other with larger selection coefficient s, using asexual travelling wave models. We find that adaptation is dominated by whichever trait has the faster rate of adaptation v in isolation, with the other trait subject to evolutionary stalling. Reviewing empirical claims for mutation-biased adaptation, we find that not all occur in the 'origin-fixation' regime of population genetics where v is only twice as sensitive to s as to U. In some cases, differences in U are at least ten to twelve times larger than differences in s, as needed to cause mutation-biased adaptation even in the 'multiple mutations' regime. Surprisingly, when U > s in the 'diffusive-mutation' regime, the required sensitivity ratio is also only two, despite pervasive clonal interference. Given two traits with identical v, the benefit of having higher s is surprisingly small, occurring largely when one trait is at the boundary between the origin-fixation and multiple mutations regimes.
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Affiliation(s)
- Kevin Gomez
- Graduate Interdisciplinary Program in Applied Mathematics, University of Arizona, Tucson, AZ, USA
| | - Jason Bertram
- Environmental Resilience Institute, Indiana University, Bloomington, IN, USA.,Department of Biology, Indiana University, Bloomington, IN, USA
| | - Joanna Masel
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
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8
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Identifying Small Molecules That Promote Quasipalindrome-Associated Template-Switch Mutations in Escherichia coli. G3-GENES GENOMES GENETICS 2020; 10:1809-1815. [PMID: 32220953 PMCID: PMC7202029 DOI: 10.1534/g3.120.401106] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
DNA can assemble into non-B form structures that stall replication and cause genomic instability. One such secondary structure results from an inverted DNA repeat that can assemble into hairpin and cruciform structures during DNA replication. Quasipalindromes (QP), imperfect inverted repeats, are sites of mutational hotspots. Quasipalindrome-associated mutations (QPMs) occur through a template-switch mechanism in which the replicative polymerase stalls at a QP site and uses the nascent strand as a template instead of the correct template strand. This mutational event causes the QP to become a perfect or more perfect inverted repeat. Since it is not fully understood how template-switch events are stimulated or repressed, we designed a high-throughput screen to discover drugs that affect these events. QP reporters were engineered in the Escherichia coli lacZ gene to allow us to study template-switch events specifically. We tested 700 compounds from the NIH Clinical Collection through a disk diffusion assay and identified 11 positive hits. One of the hits was azidothymidine (zidovudine, AZT), a thymidine analog and DNA chain terminator. The other ten were found to be fluoroquinolone antibiotics, which induce DNA-protein crosslinks. This work shows that our screen is useful in identifying small molecules that affect quasipalindrome-associated template-switch mutations. We are currently assessing more small molecule libraries and applying this method to study other types of mutations.
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9
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Castañeda-García A, Martín-Blecua I, Cebrián-Sastre E, Chiner-Oms A, Torres-Puente M, Comas I, Blázquez J. Specificity and mutagenesis bias of the mycobacterial alternative mismatch repair analyzed by mutation accumulation studies. SCIENCE ADVANCES 2020; 6:eaay4453. [PMID: 32095527 PMCID: PMC7015689 DOI: 10.1126/sciadv.aay4453] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 11/25/2019] [Indexed: 05/09/2023]
Abstract
The postreplicative mismatch repair (MMR) is an almost ubiquitous DNA repair essential for maintaining genome stability. It has been suggested that Mycobacteria have an alternative MMR in which NucS, an endonuclease with no structural homology to the canonical MMR proteins (MutS/MutL), is the key factor. Here, we analyze the spontaneous mutations accumulated in a neutral manner over thousands of generations by Mycobacterium smegmatis and its MMR-deficient derivative (ΔnucS). The base pair substitution rates per genome per generation are 0.004 and 0.165 for wild type and ΔnucS, respectively. By comparing the activity of different bacterial MMR pathways, we demonstrate that both MutS/L- and NucS-based systems display similar specificity and mutagenesis bias, revealing a functional evolutionary convergence. However, NucS is not able to repair indels in vivo. Our results provide an unparalleled view of how this mycobacterial system works in vivo to maintain genome stability and how it may affect Mycobacterium evolution.
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Affiliation(s)
- A. Castañeda-García
- Centro Nacional de Biotecnología–CSIC, Madrid, Spain
- Corresponding author. (A.C.-G.); (J.B.)
| | | | | | - A. Chiner-Oms
- Instituto de Biomedicina de Valencia, IBV-CSIC, Valencia, Spain
| | | | - I. Comas
- Instituto de Biomedicina de Valencia, IBV-CSIC, Valencia, Spain
- CIBER in Epidemiology and Public Health
| | - J. Blázquez
- Centro Nacional de Biotecnología–CSIC, Madrid, Spain
- Corresponding author. (A.C.-G.); (J.B.)
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10
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Lind PA, Libby E, Herzog J, Rainey PB. Predicting mutational routes to new adaptive phenotypes. eLife 2019; 8:e38822. [PMID: 30616716 PMCID: PMC6324874 DOI: 10.7554/elife.38822] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2018] [Accepted: 11/27/2018] [Indexed: 12/21/2022] Open
Abstract
Predicting evolutionary change poses numerous challenges. Here we take advantage of the model bacterium Pseudomonas fluorescens in which the genotype-to-phenotype map determining evolution of the adaptive 'wrinkly spreader' (WS) type is known. We present mathematical descriptions of three necessary regulatory pathways and use these to predict both the rate at which each mutational route is used and the expected mutational targets. To test predictions, mutation rates and targets were determined for each pathway. Unanticipated mutational hotspots caused experimental observations to depart from predictions but additional data led to refined models. A mismatch was observed between the spectra of WS-causing mutations obtained with and without selection due to low fitness of previously undetected WS-causing mutations. Our findings contribute toward the development of mechanistic models for forecasting evolution, highlight current limitations, and draw attention to challenges in predicting locus-specific mutational biases and fitness effects.
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Affiliation(s)
- Peter A Lind
- New Zealand Institute for Advanced StudyMassey University at AlbanyAucklandNew Zealand
- Department of Molecular BiologyUmeå UniversityUmeåSweden
| | - Eric Libby
- New Zealand Institute for Advanced StudyMassey University at AlbanyAucklandNew Zealand
- Santa Fe InstituteNew MexicoUnited States
- Department of MathematicsUmeå UniversityUmeåSweden
| | - Jenny Herzog
- New Zealand Institute for Advanced StudyMassey University at AlbanyAucklandNew Zealand
| | - Paul B Rainey
- New Zealand Institute for Advanced StudyMassey University at AlbanyAucklandNew Zealand
- Department of Microbial Population BiologyMax Planck Institute for Evolutionary BiologyPlönGermany
- Ecole Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, ESPCI Paris-TechCNRS UMR 8231, PSL Research UniversityParisFrance
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11
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Stimulation of Replication Template-Switching by DNA-Protein Crosslinks. Genes (Basel) 2018; 10:genes10010014. [PMID: 30591691 PMCID: PMC6357072 DOI: 10.3390/genes10010014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 12/10/2018] [Accepted: 12/12/2018] [Indexed: 11/16/2022] Open
Abstract
Covalent DNA protein crosslinks (DPCs) are common lesions that block replication. We examine here the consequence of DPCs on mutagenesis involving replicational template-switch reactions in Escherichia coli. 5-Azacytidine (5-azaC) is a potent mutagen for template-switching. This effect is dependent on DNA cytosine methylase (Dcm), implicating the Dcm-DNA covalent complex trapped by 5-azaC as the initiator for mutagenesis. The leading strand of replication is more mutable than the lagging strand, which can be explained by blocks to the replicative helicase and/or fork regression. We find that template-switch mutagenesis induced by 5-azaC does not require double strand break repair via RecABCD; the ability to induce the SOS response is anti-mutagenic. Mutants in recB, but not recA, exhibit high constitutive rates of template-switching, and we suggest that RecBCD-mediated DNA degradation prevents template-switching associated with fork regression. A mutation in the DnaB fork helicase also promotes high levels of template-switching. We also find that other DPC-inducers, formaldehyde (a non-specific crosslinker) and ciprofloxacin (a topoisomerase II poison) are also strong mutagens for template-switching with similar genetic properties. Induction of mutations and genetic rearrangements that occur by template-switching may constitute a previously unrecognized component of the genotoxicity and genetic instability promoted by DPCs.
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12
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Tsao WC, Eckert KA. Detours to Replication: Functions of Specialized DNA Polymerases during Oncogene-induced Replication Stress. Int J Mol Sci 2018; 19:ijms19103255. [PMID: 30347795 PMCID: PMC6214091 DOI: 10.3390/ijms19103255] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2018] [Revised: 10/15/2018] [Accepted: 10/15/2018] [Indexed: 01/10/2023] Open
Abstract
Incomplete and low-fidelity genome duplication contribute to genomic instability and cancer development. Difficult-to-Replicate Sequences, or DiToRS, are natural impediments in the genome that require specialized DNA polymerases and repair pathways to complete and maintain faithful DNA synthesis. DiToRS include non B-DNA secondary structures formed by repetitive sequences, for example within chromosomal fragile sites and telomeres, which inhibit DNA replication under endogenous stress conditions. Oncogene activation alters DNA replication dynamics and creates oncogenic replication stress, resulting in persistent activation of the DNA damage and replication stress responses, cell cycle arrest, and cell death. The response to oncogenic replication stress is highly complex and must be tightly regulated to prevent mutations and tumorigenesis. In this review, we summarize types of known DiToRS and the experimental evidence supporting replication inhibition, with a focus on the specialized DNA polymerases utilized to cope with these obstacles. In addition, we discuss different causes of oncogenic replication stress and its impact on DiToRS stability. We highlight recent findings regarding the regulation of DNA polymerases during oncogenic replication stress and the implications for cancer development.
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Affiliation(s)
- Wei-Chung Tsao
- Department of Pathology, The Jake Gittlen Laboratories for Cancer Research, Hershey, PA 17033, USA.
| | - Kristin A Eckert
- Department of Pathology, The Jake Gittlen Laboratories for Cancer Research, Hershey, PA 17033, USA.
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13
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Lavi B, Levy Karin E, Pupko T, Hazkani-Covo E. The Prevalence and Evolutionary Conservation of Inverted Repeats in Proteobacteria. Genome Biol Evol 2018; 10:918-927. [PMID: 29608719 PMCID: PMC5941160 DOI: 10.1093/gbe/evy044] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/21/2018] [Indexed: 12/11/2022] Open
Abstract
Perfect short inverted repeats (IRs) are known to be enriched in a variety of bacterial and eukaryotic genomes. Currently, it is unclear whether perfect IRs are conserved over evolutionary time scales. In this study, we aimed to characterize the prevalence and evolutionary conservation of IRs across 20 proteobacterial strains. We first identified IRs in Escherichia coli K-12 substr MG1655 and showed that they are overabundant. We next aimed to test whether this overabundance is reflected in the conservation of IRs over evolutionary time scales. To this end, for each perfect IR identified in E. coli MG1655, we collected orthologous sequences from related proteobacterial genomes. We next quantified the evolutionary conservation of these IRs, that is, the presence of the exact same IR across orthologous regions. We observed high conservation of perfect IRs: out of the 234 examined orthologous regions, 145 were more conserved than expected, which is statistically significant even after correcting for multiple testing. Our results together with previous experimental findings support a model in which imperfect IRs are corrected to perfect IRs in a preferential manner via a template switching mechanism.
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Affiliation(s)
- Bar Lavi
- Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel
- Department of Natural and Life Sciences, The Open University of Israel, Ra'anana, Israel
| | - Eli Levy Karin
- Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel
- Department of Molecular Biology & Ecology of Plants, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel
| | - Tal Pupko
- Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel
| | - Einat Hazkani-Covo
- Department of Natural and Life Sciences, The Open University of Israel, Ra'anana, Israel
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14
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Schroeder JW, Yeesin P, Simmons LA, Wang JD. Sources of spontaneous mutagenesis in bacteria. Crit Rev Biochem Mol Biol 2017; 53:29-48. [PMID: 29108429 DOI: 10.1080/10409238.2017.1394262] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Mutations in an organism's genome can arise spontaneously, that is, in the absence of exogenous stress and prior to selection. Mutations are often neutral or deleterious to individual fitness but can also provide genetic diversity driving evolution. Mutagenesis in bacteria contributes to the already serious and growing problem of antibiotic resistance. However, the negative impacts of spontaneous mutagenesis on human health are not limited to bacterial antibiotic resistance. Spontaneous mutations also underlie tumorigenesis and evolution of drug resistance. To better understand the causes of genetic change and how they may be manipulated in order to curb antibiotic resistance or the development of cancer, we must acquire a mechanistic understanding of the major sources of mutagenesis. Bacterial systems are particularly well-suited to studying mutagenesis because of their fast growth rate and the panoply of available experimental tools, but efforts to understand mutagenic mechanisms can be complicated by the experimental system employed. Here, we review our current understanding of mutagenic mechanisms in bacteria and describe the methods used to study mutagenesis in bacterial systems.
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Affiliation(s)
- Jeremy W Schroeder
- a Department of Bacteriology , University of Wisconsin - Madison , Madison , WI , USA
| | - Ponlkrit Yeesin
- a Department of Bacteriology , University of Wisconsin - Madison , Madison , WI , USA
| | - Lyle A Simmons
- b Department of Molecular, Cellular, and Developmental Biology , University of Michigan , Ann Arbor , MI , USA
| | - Jue D Wang
- a Department of Bacteriology , University of Wisconsin - Madison , Madison , WI , USA
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15
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Abstract
Replication forks frequently are challenged by lesions on the DNA template, replication-impeding DNA secondary structures, tightly bound proteins or nucleotide pool imbalance. Studies in bacteria have suggested that under these circumstances the fork may leave behind single-strand DNA gaps that are subsequently filled by homologous recombination, translesion DNA synthesis or template-switching repair synthesis. This review focuses on the template-switching pathways and how the mechanisms of these processes have been deduced from biochemical and genetic studies. I discuss how template-switching can contribute significantly to genetic instability, including mutational hotspots and frequent genetic rearrangements, and how template-switching may be elicited by replication fork damage.
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Affiliation(s)
- Susan T Lovett
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA, 2454-9110, USA.
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16
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SSB recruitment of Exonuclease I aborts template-switching in Escherichia coli. DNA Repair (Amst) 2017; 57:12-16. [PMID: 28605670 DOI: 10.1016/j.dnarep.2017.05.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 05/30/2017] [Accepted: 05/30/2017] [Indexed: 11/21/2022]
Abstract
Misalignment of a nascent strand and the use of an alternative template during DNA replication, a process termed "template-switching", can give rise to frequent mutations and genetic rearrangements. Mutational hotspots are frequently found associated with imperfect inverted repeats ("quasipalindromes" or "QPs") in many organisms, including bacteriophage, bacteria, yeast and mammals. Evidence suggests that QPs mutate by a replication template-switch whereby one copy of the inverted repeat templates synthesis of the other. To study quasipalindrome-associated mutagenesis ("QPM") more systematically, we have engineered mutational reporters in the lacZ gene of Escherichia coli, that revert to Lac+ specifically by QPM. We and others have shown that QPM is more efficient during replication of the leading strand than it is on the lagging strand. We have previously shown that QPM is elevated and that the leading-strand bias is lost in mutants lacking the major 3' ssDNA exonucleases, ExoI and ExoVII. This suggests that one or both of these exonucleases more efficiently abort template-switches on the lagging strand. Here, we show that ExoI is primarily responsible for this bias and that its ability to be recruited by single-strand DNA binding protein plays a critical role in QPM avoidance and strand bias. In addition to these stand-alone exonucleases, loss of the 3' proofreading exonuclease activity of the replicative DNA polymerase III also greatly elevates QPM. This may be because template-switching is initiated by base misincorporation, leading to polymerase dissociation and subsequent nascent strand misalignment; alternatively or additionally, the proofreading exonuclease may scavenge displaced 3' DNA that would otherwise be free to misalign.
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17
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Winiger CB, Shaw RW, Kim MJ, Moses JD, Matsuura MF, Benner SA. Expanded Genetic Alphabets: Managing Nucleotides That Lack Tautomeric, Protonated, or Deprotonated Versions Complementary to Natural Nucleotides. ACS Synth Biol 2017; 6:194-200. [PMID: 27648724 DOI: 10.1021/acssynbio.6b00193] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
2,4-Diaminopyrimidine (trivially K) and imidazo[1,2-a]-1,3,5-triazine-2(8H)-4(3H)-dione (trivially X) form a nucleobase pair with Watson-Crick geometry as part of an artificially expanded genetic information system (AEGIS). Neither K nor X can form a Watson-Crick pair with any natural nucleobase. Further, neither K nor X has an accessible tautomeric form or a protonated/deprotonated state that can form a Watson-Crick pair with any natural nucleobase. In vitro experiments show how DNA polymerase I from E. coli manages replication of DNA templates with one K:X pair, but fails with templates containing two adjacent K:X pairs. In analogous in vivo experiments, E. coli lacking dKTP/dXTP cannot rescue chloramphenicol resistance from a plasmid containing two adjacent K:X pairs. These studies identify bacteria able to serve as selection environments for engineering cells that replicate AEGIS pairs that lack forms that are Watson-Crick complementary to any natural nucleobase.
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Affiliation(s)
- Christian B. Winiger
- Foundation for Applied Molecular Evolution (FfAME), 13709 Progress Blvd. Box 17, Alachua, Florida 32615, United States
| | - Ryan W. Shaw
- Foundation for Applied Molecular Evolution (FfAME), 13709 Progress Blvd. Box 17, Alachua, Florida 32615, United States
- Firebird Biomolecular Sciences LLC, 13709 Progress Blvd. Box 7, Alachua, Florida 32615, United States
| | - Myong-Jung Kim
- Foundation for Applied Molecular Evolution (FfAME), 13709 Progress Blvd. Box 17, Alachua, Florida 32615, United States
- Firebird Biomolecular Sciences LLC, 13709 Progress Blvd. Box 7, Alachua, Florida 32615, United States
| | - Jennifer D. Moses
- Foundation for Applied Molecular Evolution (FfAME), 13709 Progress Blvd. Box 17, Alachua, Florida 32615, United States
- Firebird Biomolecular Sciences LLC, 13709 Progress Blvd. Box 7, Alachua, Florida 32615, United States
| | - Mariko F. Matsuura
- Foundation for Applied Molecular Evolution (FfAME), 13709 Progress Blvd. Box 17, Alachua, Florida 32615, United States
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Steven A. Benner
- Foundation for Applied Molecular Evolution (FfAME), 13709 Progress Blvd. Box 17, Alachua, Florida 32615, United States
- Firebird Biomolecular Sciences LLC, 13709 Progress Blvd. Box 7, Alachua, Florida 32615, United States
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18
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Couce A, Alonso-Rodriguez N, Costas C, Oliver A, Blázquez J. Intrapopulation variability in mutator prevalence among urinary tract infection isolates of Escherichia coli. Clin Microbiol Infect 2016; 22:566.e1-7. [DOI: 10.1016/j.cmi.2016.03.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 03/09/2016] [Accepted: 03/11/2016] [Indexed: 11/29/2022]
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19
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Couce A, Rodríguez-Rojas A, Blázquez J. Bypass of genetic constraints during mutator evolution to antibiotic resistance. Proc Biol Sci 2015; 282:20142698. [PMID: 25716795 DOI: 10.1098/rspb.2014.2698] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Genetic constraints can block many mutational pathways to optimal genotypes in real fitness landscapes, yet the extent to which this can limit evolution remains to be determined. Interestingly, mutator bacteria elevate only specific types of mutations, and therefore could be very sensitive to genetic constraints. Testing this possibility is not only clinically relevant, but can also inform about the general impact of genetic constraints in adaptation. Here, we evolved 576 populations of two mutator and one wild-type Escherichia coli to doubling concentrations of the antibiotic cefotaxime. All strains carried TEM-1, a β-lactamase enzyme well known by its low availability of mutational pathways. Crucially, one of the mutators does not elevate any of the relevant first-step mutations known to improve cefatoximase activity. Despite this, both mutators displayed a similar ability to evolve more than 1000-fold resistance. Initial adaptation proceeded in parallel through general multi-drug resistance mechanisms. High-level resistance, in contrast, was achieved through divergent paths; with the a priori inferior mutator exploiting alternative mutational pathways in PBP3, the target of the antibiotic. These results have implications for mutator management in clinical infections and, more generally, illustrate that limits to natural selection in real organisms are alleviated by the existence of multiple loci contributing to fitness.
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Affiliation(s)
- Alejandro Couce
- Centro Nacional de Biotecnología (CNB-CSIC), 28049 Madrid, Spain Unité Mixte de Recherche 1137 (IAME-INSERM), 75018 Paris, France
| | - Alexandro Rodríguez-Rojas
- Centro Nacional de Biotecnología (CNB-CSIC), 28049 Madrid, Spain Institut für Biologie, Freie Universität Berlin, 14195 Berlin, Germany
| | - Jesús Blázquez
- Centro Nacional de Biotecnología (CNB-CSIC), 28049 Madrid, Spain Instituto de Biomedicina de Sevilla (IBIS), 41013 Sevilla, Spain
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20
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Northam MR, Moore EA, Mertz TM, Binz SK, Stith CM, Stepchenkova EI, Wendt KL, Burgers PMJ, Shcherbakova PV. DNA polymerases ζ and Rev1 mediate error-prone bypass of non-B DNA structures. Nucleic Acids Res 2013; 42:290-306. [PMID: 24049079 PMCID: PMC3874155 DOI: 10.1093/nar/gkt830] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
DNA polymerase ζ (Pol ζ) and Rev1 are key players in translesion DNA synthesis. The error-prone Pol ζ can also participate in replication of undamaged DNA when the normal replisome is impaired. Here we define the nature of the replication disturbances that trigger the recruitment of error-prone polymerases in the absence of DNA damage and describe the specific roles of Rev1 and Pol ζ in handling these disturbances. We show that Pol ζ/Rev1-dependent mutations occur at sites of replication stalling at short repeated sequences capable of forming hairpin structures. The Rev1 deoxycytidyl transferase can take over the stalled replicative polymerase and incorporate an additional 'C' at the hairpin base. Full hairpin bypass often involves template-switching DNA synthesis, subsequent realignment generating multiply mismatched primer termini and extension of these termini by Pol ζ. The postreplicative pathway dependent on polyubiquitylation of proliferating cell nuclear antigen provides a backup mechanism for accurate bypass of these sequences that is primarily used when the Pol ζ/Rev1-dependent pathway is inactive. The results emphasize the pivotal role of noncanonical DNA structures in mutagenesis and reveal the long-sought-after mechanism of complex mutations that represent a unique signature of Pol ζ.
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Affiliation(s)
- Matthew R Northam
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68118, USA and Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
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21
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Genomewide screen for modulators of evolvability under toxic antibiotic exposure. Antimicrob Agents Chemother 2013; 57:3453-6. [PMID: 23669383 DOI: 10.1128/aac.02454-12] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Antibiotic resistance is generally selected within a window of concentrations high enough to inhibit wild-type growth but low enough for new resistant mutants to emerge. We studied de novo evolution of resistance to ciprofloxacin in an Escherichia coli knockout library. Five null mutations had little or no effect on intrinsic antibiotic susceptibility but increased the upper antibiotic dosage to which initially sensitive populations could adapt. These mutations affect mismatch repair, translation fidelity, and iron homeostasis.
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22
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Wojcik EA, Brzostek A, Bacolla A, Mackiewicz P, Vasquez KM, Korycka-Machala M, Jaworski A, Dziadek J. Direct and inverted repeats elicit genetic instability by both exploiting and eluding DNA double-strand break repair systems in mycobacteria. PLoS One 2012; 7:e51064. [PMID: 23251422 PMCID: PMC3519483 DOI: 10.1371/journal.pone.0051064] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Accepted: 10/29/2012] [Indexed: 12/02/2022] Open
Abstract
Repetitive DNA sequences with the potential to form alternative DNA conformations, such as slipped structures and cruciforms, can induce genetic instability by promoting replication errors and by serving as a substrate for DNA repair proteins, which may lead to DNA double-strand breaks (DSBs). However, the contribution of each of the DSB repair pathways, homologous recombination (HR), non-homologous end-joining (NHEJ) and single-strand annealing (SSA), to this sort of genetic instability is not fully understood. Herein, we assessed the genome-wide distribution of repetitive DNA sequences in the Mycobacterium smegmatis, Mycobacterium tuberculosis and Escherichia coli genomes, and determined the types and frequencies of genetic instability induced by direct and inverted repeats, both in the presence and in the absence of HR, NHEJ, and SSA. All three genomes are strongly enriched in direct repeats and modestly enriched in inverted repeats. When using chromosomally integrated constructs in M. smegmatis, direct repeats induced the perfect deletion of their intervening sequences ~1,000-fold above background. Absence of HR further enhanced these perfect deletions, whereas absence of NHEJ or SSA had no influence, suggesting compromised replication fidelity. In contrast, inverted repeats induced perfect deletions only in the absence of SSA. Both direct and inverted repeats stimulated excision of the constructs from the attB integration sites independently of HR, NHEJ, or SSA. With episomal constructs, direct and inverted repeats triggered DNA instability by activating nucleolytic activity, and absence of the DSB repair pathways (in the order NHEJ>HR>SSA) exacerbated this instability. Thus, direct and inverted repeats may elicit genetic instability in mycobacteria by 1) directly interfering with replication fidelity, 2) stimulating the three main DSB repair pathways, and 3) enticing L5 site-specific recombination.
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Affiliation(s)
- Ewelina A. Wojcik
- Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland
- Department of Genetics of Microorganisms, Institute of Microbiology and Immunology, University of Lodz, Lodz, Poland
| | - Anna Brzostek
- Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland
| | - Albino Bacolla
- The University of Texas at Austin, Division of Pharmacology and Toxicology, Dell Pediatric Research Institute, Austin, Texas, United States of America
| | - Pawel Mackiewicz
- Department of Genomics, Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland
| | - Karen M. Vasquez
- The University of Texas at Austin, Division of Pharmacology and Toxicology, Dell Pediatric Research Institute, Austin, Texas, United States of America
| | | | - Adam Jaworski
- Department of Genetics of Microorganisms, Institute of Microbiology and Immunology, University of Lodz, Lodz, Poland
| | - Jaroslaw Dziadek
- Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland
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23
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Walsh E, Wang X, Lee MY, Eckert KA. Mechanism of replicative DNA polymerase delta pausing and a potential role for DNA polymerase kappa in common fragile site replication. J Mol Biol 2012; 425:232-43. [PMID: 23174185 DOI: 10.1016/j.jmb.2012.11.016] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2012] [Revised: 11/12/2012] [Accepted: 11/12/2012] [Indexed: 11/16/2022]
Abstract
Common fragile sites (CFSs) are hot spots of chromosomal breakage, and CFS breakage models involve perturbations of DNA replication. Here, we analyzed the contribution of specific repetitive DNA sequence elements within CFSs to the inhibition of DNA synthesis by replicative and specialized DNA polymerases (Pols). The efficiency of in vitro DNA synthesis was quantitated using templates corresponding to regions within FRA16D and FRA3B harboring AT-rich microsatellite and quasi-palindrome (QP) sequences. QPs were predicted to form stems of ~75-100% self-homology, separated by 3-9 bases of intervening sequences. Analysis of DNA synthesis progression by human Pol δ demonstrated significant synthesis perturbation both at [A](n) and [TA](n) repeats in a length-dependent manner and at short (<40 base pairs) QP sequences. DNA synthesis by the Y-family polymerase κ was significantly more efficient than Pol δ through both types of repetitive elements. Using DNA trap experiments, we show that Pol δ pauses within CFS sequences are sites of enzyme dissociation, and dissociation was observed in the presence of RFC-loaded PCNA. We propose that enrichment of microsatellite and QP elements at CFS regions contributes to fragility by perturbing replication through multiple mechanisms, including replicative Pol pausing and dissociation. Our finding that Pol δ dissociates at specific CFS sequences is significant, since dissociation of the replication machinery and inability to efficiently recover the replication fork can lead to fork collapse and/or formation of double-strand breaks in vivo. Our biochemical studies also extend the potential involvement of Y-family polymerases in CFS maintenance to include polymerase κ.
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Affiliation(s)
- Erin Walsh
- Cellular and Molecular Biology Graduate Program, Penn State University College of Medicine, Hershey, PA 17033, USA
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24
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Azidothymidine and other chain terminators are mutagenic for template-switch-generated genetic mutations. Proc Natl Acad Sci U S A 2012; 109:6171-4. [PMID: 22474374 DOI: 10.1073/pnas.1116160109] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The accumulation of mutations causes cell lethality and can lead to carcinogenesis. An important class of mutations, which are associated with mutational hotspots in many organisms, are those that arise by nascent strand misalignment and template-switching at the site of short repetitive sequences in DNA. Mutagens that strongly and specifically affect this class, which is mechanistically distinct from other mutations that arise from polymerase errors or by DNA template damage, are unknown. Using Escherichia coli and assays for specific mutational events, this study defines such a mutagen, 3'-azidothymidine [zidovudine (AZT)], used widely in the treatment and prevention of HIV/AIDS. At sublethal doses, AZT has no significant effect on frame shifts and most base-substitution mutations. AT-to-CG transversions and deletions at microhomologies were enhanced modestly by AZT. AZT strongly stimulated the "template-switch" class of mutations that arise in imperfect inverted repeat sequences by DNA-strand misalignments during replication, presumably through its action as a chain terminator during DNA replication. Chain-terminating 2'-3'-didehydro 3'-deoxythymidine [stavudine (D4T)] and 2'-3'-dideoxyinosine [didanosine (ddI)] likewise stimulated template-switch mutagenesis. These agents define a specific class of mutagen that promotes template-switching and acts by stalling replication rather than by direct nucleotide base damage.
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25
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Tashiro Y, Katabami A, Saito K, Umeno D. A system for the rapid determination of the mutation spectrum in Escherichia coli. ANAL SCI 2012; 28:95-101. [PMID: 22322800 DOI: 10.2116/analsci.28.95] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The first step toward elucidating the mutagenic effects of chemicals and pathways is to determine the specificity of the mutations generated spontaneously or in response to treatment with mutagens. We constructed a set of plasmid-encoded probes for the specific detection of each type of base substitution mutation. Using these probes, we were able to quickly determine both the mutation rate and the specificity of the mutations caused by different types of mutagens and mutagenic conditions. We also developed a PCR-based method to rapidly and robustly determine the mutation spectrum in response to various mutagenic samples in parallel. This system allows one to not only analyze the mutation specificity of various chemicals, but also to search for novel genetic elements that promote the specific mutation events.
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Affiliation(s)
- Yohei Tashiro
- Department of Applied Chemistry and Biotechnology, Chiba University, 1-33 Yayoi, Inage, Chiba 263–8522, Japan
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