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The Functional Consequences of Eukaryotic Topoisomerase 1 Interaction with G-Quadruplex DNA. Genes (Basel) 2020; 11:genes11020193. [PMID: 32059547 PMCID: PMC7073998 DOI: 10.3390/genes11020193] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 02/07/2020] [Accepted: 02/09/2020] [Indexed: 12/22/2022] Open
Abstract
Topoisomerase I in eukaryotic cells is an important regulator of DNA topology. Its catalytic function is to remove positive or negative superhelical tension by binding to duplex DNA, creating a reversible single-strand break, and finally religating the broken strand. Proper maintenance of DNA topological homeostasis, in turn, is critically important in the regulation of replication, transcription, DNA repair, and other processes of DNA metabolism. One of the cellular processes regulated by the DNA topology and thus by Topoisomerase I is the formation of non-canonical DNA structures. Non-canonical or non-B DNA structures, including the four-stranded G-quadruplex or G4 DNA, are potentially pathological in that they interfere with replication or transcription, forming hotspots of genome instability. In this review, we first describe the role of Topoisomerase I in reducing the formation of non-canonical nucleic acid structures in the genome. We further discuss the interesting recent discovery that Top1 and Top1 mutants bind to G4 DNA structures in vivo and in vitro and speculate on the possible consequences of these interactions.
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52
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Shyian M, Albert B, Zupan AM, Ivanitsa V, Charbonnet G, Dilg D, Shore D. Fork pausing complex engages topoisomerases at the replisome. Genes Dev 2019; 34:87-98. [PMID: 31805522 PMCID: PMC6938670 DOI: 10.1101/gad.331868.119] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Accepted: 11/07/2019] [Indexed: 12/22/2022]
Abstract
In this study, Shyian et al. set out to address mechanistically how the evolutionarily conserved fork pausing complex acts at proteinaceous replication fork barriers (RFBs) to promote fork passage and genome stability. Using several molecular and cell-based assays, the authors propose that forks pause at proteinaceous RFBs through a “sTOP” mechanism (“slowing down with topoisomerases I–II”), which also contributes to protecting cells from topoisomerase-blocking agents. Replication forks temporarily or terminally pause at hundreds of hard-to-replicate regions around the genome. A conserved pair of budding yeast replisome components Tof1–Csm3 (fission yeast Swi1–Swi3 and human TIMELESS–TIPIN) act as a “molecular brake” and promote fork slowdown at proteinaceous replication fork barriers (RFBs), while the accessory helicase Rrm3 assists the replisome in removing protein obstacles. Here we show that the Tof1–Csm3 complex promotes fork pausing independently of Rrm3 helicase by recruiting topoisomerase I (Top1) to the replisome. Topoisomerase II (Top2) partially compensates for the pausing decrease in cells when Top1 is lost from the replisome. The C terminus of Tof1 is specifically required for Top1 recruitment to the replisome and fork pausing but not for DNA replication checkpoint (DRC) activation. We propose that forks pause at proteinaceous RFBs through a “sTOP” mechanism (“slowing down with topoisomerases I–II”), which we show also contributes to protecting cells from topoisomerase-blocking agents.
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Affiliation(s)
- Maksym Shyian
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
| | - Benjamin Albert
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
| | - Andreja Moset Zupan
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
| | - Vitalii Ivanitsa
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
| | - Gabriel Charbonnet
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
| | - Daniel Dilg
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
| | - David Shore
- Department of Molecular Biology, Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, Geneva 4, CH-1211, Switzerland
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53
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Hawkins M, Dimude JU, Howard JAL, Smith AJ, Dillingham MS, Savery NJ, Rudolph CJ, McGlynn P. Direct removal of RNA polymerase barriers to replication by accessory replicative helicases. Nucleic Acids Res 2019; 47:5100-5113. [PMID: 30869136 PMCID: PMC6547429 DOI: 10.1093/nar/gkz170] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 02/22/2019] [Accepted: 03/08/2019] [Indexed: 11/24/2022] Open
Abstract
Bacterial genome duplication and transcription require simultaneous access to the same DNA template. Conflicts between the replisome and transcription machinery can lead to interruption of DNA replication and loss of genome stability. Pausing, stalling and backtracking of transcribing RNA polymerases add to this problem and present barriers to replisomes. Accessory helicases promote fork movement through nucleoprotein barriers and exist in viruses, bacteria and eukaryotes. Here, we show that stalled Escherichia coli transcription elongation complexes block reconstituted replisomes. This physiologically relevant block can be alleviated by the accessory helicase Rep or UvrD, resulting in the formation of full-length replication products. Accessory helicase action during replication-transcription collisions therefore promotes continued replication without leaving gaps in the DNA. In contrast, DinG does not promote replisome movement through stalled transcription complexes in vitro. However, our data demonstrate that DinG operates indirectly in vivo to reduce conflicts between replication and transcription. These results suggest that Rep and UvrD helicases operate on DNA at the replication fork whereas DinG helicase acts via a different mechanism.
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Affiliation(s)
- Michelle Hawkins
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Juachi U Dimude
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | | | - Abigail J Smith
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
| | - Mark S Dillingham
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
| | - Nigel J Savery
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
| | - Christian J Rudolph
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | - Peter McGlynn
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
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54
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Su N, Byrd AK, Bharath SR, Yang O, Jia Y, Tang X, Ha T, Raney KD, Song H. Structural basis for DNA unwinding at forked dsDNA by two coordinating Pif1 helicases. Nat Commun 2019; 10:5375. [PMID: 31772234 PMCID: PMC6879534 DOI: 10.1038/s41467-019-13414-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 11/05/2019] [Indexed: 11/25/2022] Open
Abstract
Pif1 plays multiple roles in maintaining genome stability and preferentially unwinds forked dsDNA, but the mechanism by which Pif1 unwinds forked dsDNA remains elusive. Here we report the structure of Bacteroides sp Pif1 (BaPif1) in complex with a symmetrical double forked dsDNA. Two interacting BaPif1 molecules are bound to each fork of the partially unwound dsDNA, and interact with the 5′ arm and 3′ ss/dsDNA respectively. Each of the two BaPif1 molecules is an active helicase and their interaction may regulate their helicase activities. The binding of BaPif1 to the 5′ arm causes a sharp bend in the 5′ ss/dsDNA junction, consequently breaking the first base-pair. BaPif1 bound to the 3′ ss/dsDNA junction impacts duplex unwinding by stabilizing the unpaired first base-pair and engaging the second base-pair poised for breaking. Our results provide an unprecedented insight into how two BaPif1 coordinate with each other to unwind the forked dsDNA. Pif1 plays multiple roles in maintaining genome stability and preferentially unwinds forked dsDNA. Here the authors solve the structure of Bacteroides sp Pif1 (BaPif1) in complex with a symmetrical double forked dsDNA and provide unprecedented insights into forked dsDNA unwinding by BaPif1.
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Affiliation(s)
- Nannan Su
- Life Sciences Institute, Zhejiang University, 388 Yuhangtang Road, Hangzhou, 310058, China.,Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore, 138673, Singapore
| | - Alicia K Byrd
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, 72205, USA
| | - Sakshibeedu R Bharath
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore, 138673, Singapore
| | - Olivia Yang
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University, 725N. Wolfe Street, Baltimore, MD, 21205, USA
| | - Yu Jia
- Life Sciences Institute, Zhejiang University, 388 Yuhangtang Road, Hangzhou, 310058, China.,Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore, 138673, Singapore
| | - Xuhua Tang
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore, 138673, Singapore
| | - Taekjip Ha
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University, 725N. Wolfe Street, Baltimore, MD, 21205, USA.
| | - Kevin D Raney
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, 72205, USA.
| | - Haiwei Song
- Life Sciences Institute, Zhejiang University, 388 Yuhangtang Road, Hangzhou, 310058, China. .,Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore, 138673, Singapore. .,Department of Biochemistry, National University of Singapore, 14 Science Drive, Singapore, 117543, Singapore.
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55
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Meng X, Wei L, Peng XP, Zhao X. Sumoylation of the DNA polymerase ε by the Smc5/6 complex contributes to DNA replication. PLoS Genet 2019; 15:e1008426. [PMID: 31765372 PMCID: PMC6876774 DOI: 10.1371/journal.pgen.1008426] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Accepted: 09/16/2019] [Indexed: 12/27/2022] Open
Abstract
DNA polymerase epsilon (Pol ε) is critical for genome duplication, but little is known about how post-translational modification regulates its function. Here we report that the Pol ε catalytic subunit Pol2 in yeast is sumoylated at a single lysine within a catalytic domain insertion uniquely possessed by Pol2 family members. We found that Pol2 sumoylation occurs specifically in S phase and is increased under conditions of replication fork blockade. Analyses of the genetic requirements of this modification indicate that Pol2 sumoylation is associated with replication fork progression and dependent on the Smc5/6 SUMO ligase known to promote DNA synthesis. Consistently, the pol2 sumoylation mutant phenotype suggests impaired replication progression and increased levels of gross chromosomal rearrangements. Our findings thus indicate a direct role for SUMO in Pol2-mediated DNA synthesis and a molecular basis for Smc5/6-mediated regulation of genome stability. DNA replication factors are tightly regulated to ensure genome duplication accuracy and efficiency. Among these factors, the Pol ε replicative polymerase plays a vital role by copying half of the genome every cell cycle. However, little is known about how this critical enzyme is regulated. Here we describe SUMO-based regulation of the catalytic subunit of Pol ε, Pol2. Our data suggest that Pol2 sumoylation occurs during replication elongation, particularly when replication forks encounter template obstacles. This modification is mediated by the conserved Smc5/6 SUMO ligase complex and occurs at a single site within the Pol2 catalytic domain. Several observations suggest that Pol2 sumoylation makes positive contributions to the synthesis of DNA regions enriched with template barriers and helps to prevent large-scale genomic alterations. Our work thus provides new insights into DNA polymerase regulation, specifically the role played by contributions from SUMO and the Smc5/6 complex.
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Affiliation(s)
- Xiangzhou Meng
- Molecular Biology Department, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
| | - Lei Wei
- Molecular Biology Department, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
| | - Xiao P. Peng
- Molecular Biology Department, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
- Tri-Institutional MD-PhD Program of Weill Cornell Medical School, Rockefeller University, and Sloan-Kettering Cancer Center, New York, New York, United States of America
| | - Xiaolan Zhao
- Molecular Biology Department, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
- * E-mail:
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56
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Chen CF, Pohl TJ, Chan A, Slocum JS, Zakian VA. Saccharomyces cerevisiae Centromere RNA Is Negatively Regulated by Cbf1 and Its Unscheduled Synthesis Impacts CenH3 Binding. Genetics 2019; 213:465-479. [PMID: 31391265 PMCID: PMC6781895 DOI: 10.1534/genetics.119.302528] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 07/19/2019] [Indexed: 12/12/2022] Open
Abstract
Two common features of centromeres are their transcription into noncoding centromere RNAs (cen-RNAs) and their assembly into nucleosomes that contain a centromere-specific histone H3 (cenH3). Here, we show that Saccharomyces cerevisiae cen-RNA was present in low amounts in wild-type (WT) cells, and that its appearance was tightly cell cycle-regulated, appearing and disappearing in a narrow window in S phase after centromere replication. In cells lacking Cbf1, a centromere-binding protein, cen-RNA was 5-12 times more abundant throughout the cell cycle. In WT cells, cen-RNA appearance occurred at the same time as loss of Cbf1's centromere binding, arguing that the physical presence of Cbf1 inhibits cen-RNA production. Binding of the Pif1 DNA helicase, which happens in mid-late S phase, occurred at about the same time as Cbf1 loss from the centromere, suggesting that Pif1 may facilitate this loss by its known ability to displace proteins from DNA. Cen-RNAs were more abundant in rnh1Δ cells but only in mid-late S phase. However, fork pausing at centromeres was not elevated in rnh1Δ cells but rather was due to centromere-binding proteins, including Cbf1 Strains with increased cen-RNA lost centromere plasmids at elevated rates. In cbf1Δ cells, where both the levels and the cell cycle-regulated appearance of cen-RNA were disrupted, the timing and levels of cenH3 centromere binding were perturbed. Thus, cen-RNAs are highly regulated, and disruption of this regulation correlates with changes in centromere structure and function.
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Affiliation(s)
- Chi-Fu Chen
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, New Jersey 08544
| | - Thomas J Pohl
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, New Jersey 08544
| | - Angela Chan
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, New Jersey 08544
| | - Joshua S Slocum
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, New Jersey 08544
| | - Virginia A Zakian
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, New Jersey 08544
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57
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Rowlands H, Shaban K, Foster B, Proteau Y, Yankulov K. Histone chaperones and the Rrm3p helicase regulate flocculation in S. cerevisiae. Epigenetics Chromatin 2019; 12:56. [PMID: 31547833 PMCID: PMC6757361 DOI: 10.1186/s13072-019-0303-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2019] [Accepted: 09/03/2019] [Indexed: 12/16/2022] Open
Abstract
Background Biofilm formation or flocculation is a major phenotype in wild type budding yeasts but rarely seen in laboratory yeast strains. Here, we analysed flocculation phenotypes and the expression of FLO genes in laboratory strains with various genetic backgrounds. Results We show that mutations in histone chaperones, the helicase RRM3 and the Histone Deacetylase HDA1 de-repress the FLO genes and partially reconstitute flocculation. We demonstrate that the loss of repression correlates to elevated expression of several FLO genes, to increased acetylation of histones at the promoter of FLO1 and to variegated expression of FLO11. We show that these effects are related to the activity of CAF-1 at the replication forks. We also demonstrate that nitrogen starvation or inhibition of histone deacetylases do not produce flocculation in W303 and BY4742 strains but do so in strains compromised for chromatin maintenance. Finally, we correlate the de-repression of FLO genes to the loss of silencing at the subtelomeric and mating type gene loci. Conclusions We conclude that the deregulation of chromatin maintenance and transmission is sufficient to reconstitute flocculation in laboratory yeast strains. Consequently, we propose that a gain in epigenetic silencing is a major contributing factor for the loss of flocculation phenotypes in these strains. We suggest that flocculation in yeasts provides an excellent model for addressing the challenging issue of how epigenetic mechanisms contribute to evolution.
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Affiliation(s)
- Hollie Rowlands
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada
| | - Kholoud Shaban
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada
| | - Barret Foster
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada
| | - Yannic Proteau
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada
| | - Krassimir Yankulov
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada.
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58
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Yeast PAF1 complex counters the pol III accumulation and replication stress on the tRNA genes. Sci Rep 2019; 9:12892. [PMID: 31501524 PMCID: PMC6733944 DOI: 10.1038/s41598-019-49316-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Accepted: 08/21/2019] [Indexed: 12/13/2022] Open
Abstract
The RNA polymerase (pol) III transcribes mostly short, house-keeping genes, which produce stable, non-coding RNAs. The tRNAs genes, highly transcribed by pol III in vivo are known replication fork barriers. One of the transcription factors, the PAF1C (RNA polymerase II associated factor 1 complex) is reported to associate with pol I and pol II and influence their transcription. We found low level PAF1C occupancy on the yeast pol III-transcribed genes, which is not correlated with nucleosome positions, pol III occupancy and transcription. PAF1C interacts with the pol III transcription complex and causes pol III loss from the genes under replication stress. Genotoxin exposure causes pol III but not Paf1 loss from the genes. In comparison, Paf1 deletion leads to increased occupancy of pol III, γ-H2A and DNA pol2 in gene-specific manner. Paf1 restricts the accumulation of pol III by influencing the pol III pause on the genes, which reduces the pol III barrier to the replication fork progression.
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59
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Lu KY, Chen WF, Rety S, Liu NN, Wu WQ, Dai YX, Li D, Ma HY, Dou SX, Xi XG. Insights into the structural and mechanistic basis of multifunctional S. cerevisiae Pif1p helicase. Nucleic Acids Res 2019; 46:1486-1500. [PMID: 29202194 PMCID: PMC5814829 DOI: 10.1093/nar/gkx1217] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 11/23/2017] [Indexed: 12/23/2022] Open
Abstract
The Saccharomyces cerevisiae Pif1 protein (ScPif1p) is the prototypical member of the Pif1 family of DNA helicases. ScPif1p is involved in the maintenance of mitochondrial, ribosomal and telomeric DNA and suppresses genome instability at G-quadruplex motifs. Here, we report the crystal structures of a truncated ScPif1p (ScPif1p237−780) in complex with different ssDNAs. Our results have revealed that a yeast-specific insertion domain protruding from the 2B domain folds as a bundle bearing an α-helix, α16. The α16 helix regulates the helicase activities of ScPif1p through interactions with the previously identified loop3. Furthermore, a biologically relevant dimeric structure has been identified, which can be further specifically stabilized by G-quadruplex DNA. Basing on structural analyses and mutational studies with DNA binding and unwinding assays, a potential G-quadruplex DNA binding site in ScPif1p monomers is suggested. Our results also show that ScPif1p uses the Q-motif to preferentially hydrolyze ATP, and a G-rich tract is preferentially recognized by more residues, consistent with previous biochemical observations. These findings provide a structural and mechanistic basis for understanding the multifunctional ScPif1p.
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Affiliation(s)
- Ke-Yu Lu
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Wei-Fei Chen
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Stephane Rety
- Univ. Lyon, ENS de Lyon, Univ. Claude Bernard, CNRS UMR 5239, INSERM U1210, LBMC, 46 allée d'Italie Site Jacques Monod, F-69007 Lyon, France
| | - Na-Nv Liu
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Wen-Qiang Wu
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Yang-Xue Dai
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Dan Li
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Hai-Yun Ma
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Shuo-Xing Dou
- Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xu-Guang Xi
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.,Laboratoire de Biologie et Pharmacologie Appliquée, Ecole Normale Supérieure de Cachan, Université Paris-Saclay, Centre National de la Recherche Scientifique, 61 Avenue du Président Wilson, 94235 Cachan, France
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60
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Hizume K, Araki H. Replication fork pausing at protein barriers on chromosomes. FEBS Lett 2019; 593:1449-1458. [PMID: 31199500 DOI: 10.1002/1873-3468.13481] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 06/07/2019] [Accepted: 06/10/2019] [Indexed: 12/16/2022]
Abstract
When a cell divides prior to completion of DNA replication, serious DNA damage may occur. Thus, in addition to accuracy, the processivity of the replication forks is important. DNA synthesis at replication forks should be completed in time, and forks overcome aberrant structures on the template DNA, including damaged sites, using trans-lesion synthesis, occasionally introducing mutations. By contrast, the protein barrier built on the DNA is known to block the progression of replication forks at specific chromosomal loci. Such protein barriers avert any collision of replication and transcription machineries, or control the recombination of specific loci. The components and the mechanisms of action of protein barriers have been revealed mainly using genetic and biochemical techniques. In addition to proteins involved in replication fork pausing, the interaction of the replicative helicase and DNA polymerase is also essential for replication fork pausing. Here, we provide an overview of replication fork pausing at protein barriers.
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Affiliation(s)
- Kohji Hizume
- Division of RI Laboratory, Biomedical Research Center, Saitama Medical University, Japan
| | - Hiroyuki Araki
- Microbial Genetics Laboratory, National Institute of Genetics, Mishima, Japan.,Department of Genetics, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Mishima, Japan
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61
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García-Rodríguez N, Wong RP, Ulrich HD. The helicase Pif1 functions in the template switching pathway of DNA damage bypass. Nucleic Acids Res 2019; 46:8347-8356. [PMID: 30107417 PMCID: PMC6144865 DOI: 10.1093/nar/gky648] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Accepted: 08/08/2018] [Indexed: 11/13/2022] Open
Abstract
Replication of damaged DNA is challenging because lesions in the replication template frequently interfere with an orderly progression of the replisome. In this situation, complete duplication of the genome is ensured by the action of DNA damage bypass pathways effecting either translesion synthesis by specialized, damage-tolerant DNA polymerases or a recombination-like mechanism called template switching (TS). Here we report that budding yeast Pif1, a helicase known to be involved in the resolution of complex DNA structures as well as the maturation of Okazaki fragments during replication, contributes to DNA damage bypass. We show that Pif1 expands regions of single-stranded DNA, so-called daughter-strand gaps, left behind the replication fork as a consequence of replisome re-priming. This function requires interaction with the replication clamp, proliferating cell nuclear antigen, facilitating its recruitment to damage sites, and complements the activity of an exonuclease, Exo1, in the processing of post-replicative daughter-strand gaps in preparation for TS. Our results thus reveal a novel function of a conserved DNA helicase that is known as a key player in genome maintenance.
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Affiliation(s)
| | - Ronald P Wong
- Institute of Molecular Biology (IMB), Ackermannweg 4, D-55128 Mainz, Germany
| | - Helle D Ulrich
- Institute of Molecular Biology (IMB), Ackermannweg 4, D-55128 Mainz, Germany
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62
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Brüning JG, Howard JAL, Myka KK, Dillingham MS, McGlynn P. The 2B subdomain of Rep helicase links translocation along DNA with protein displacement. Nucleic Acids Res 2019; 46:8917-8925. [PMID: 30060236 PMCID: PMC6158625 DOI: 10.1093/nar/gky673] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Accepted: 07/17/2018] [Indexed: 12/22/2022] Open
Abstract
Helicases catalyse DNA and RNA strand separation. Proteins bound to the nucleic acid must also be displaced in order to unwind DNA. This is exemplified by accessory helicases that clear protein barriers from DNA ahead of advancing replication forks. How helicases catalyse DNA unwinding is increasingly well understood but how protein displacement is achieved is unclear. Escherichia coli Rep accessory replicative helicase lacking one of its four subdomains, 2B, has been shown to be hyperactivated for DNA unwinding in vitro but we show here that RepΔ2B is, in contrast, deficient in displacing proteins from DNA. This defect correlates with an inability to promote replication of protein-bound DNA in vitro and lack of accessory helicase function in vivo. Defective protein displacement is manifested on double-stranded and single-stranded DNA. Thus binding and distortion of duplex DNA by the 2B subdomain ahead of the helicase is not the missing function responsible for this deficiency. These data demonstrate that protein displacement from DNA is not simply achieved by helicase translocation alone. They also imply that helicases may have evolved different specific features to optimise DNA unwinding and protein displacement, both of which are now recognised as key functions in all aspects of nucleic acid metabolism.
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Affiliation(s)
| | | | - Kamila K Myka
- Department of Biology, University of York, York YO10 5DD, UK
| | - Mark S Dillingham
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Biomedical Sciences Building, University Walk, Bristol BS8 1TD, UK
| | - Peter McGlynn
- Department of Biology, University of York, York YO10 5DD, UK
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63
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Pohl TJ, Zakian VA. Pif1 family DNA helicases: A helpmate to RNase H? DNA Repair (Amst) 2019; 84:102633. [PMID: 31231063 DOI: 10.1016/j.dnarep.2019.06.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 06/14/2019] [Accepted: 06/14/2019] [Indexed: 01/21/2023]
Abstract
An R-loop is a structure that forms when an RNA transcript stays bound to the DNA strand that encodes it and leaves the complementary strand exposed as a loop of single stranded DNA. R-loops accumulate when the processing of RNA transcripts is impaired. The failure to remove these RNA-DNA hybrids can lead to replication fork stalling and genome instability. Resolution of R-loops is thought to be mediated mainly by RNase H enzymes through the removal and degradation of the RNA in the hybrid. However, DNA helicases can also dismantle R-loops by displacing the bound RNA. In particular, the Pif1 family DNA helicases have been shown to regulate R-loop formation at specific genomic loci, such as tRNA genes and centromeres. Here we review the roles of Pif1 family helicases in vivo and in vitro and discuss evidence that Pif1 family helicases act on RNA-DNA hybrids and highlight their potential roles in complementing RNase H for R-loop resolution.
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Affiliation(s)
- Thomas J Pohl
- Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, United States
| | - Virginia A Zakian
- Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, United States.
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64
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Tamang S, Kishkevich A, Morrow CA, Osman F, Jalan M, Whitby MC. The PCNA unloader Elg1 promotes recombination at collapsed replication forks in fission yeast. eLife 2019; 8:47277. [PMID: 31149897 PMCID: PMC6544435 DOI: 10.7554/elife.47277] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 05/14/2019] [Indexed: 12/20/2022] Open
Abstract
Protein-DNA complexes can impede DNA replication and cause replication fork collapse. Whilst it is known that homologous recombination is deployed in such instances to restart replication, it is unclear how a stalled fork transitions into a collapsed fork at which recombination proteins can load. Previously we established assays in Schizosaccharomyces pombe for studying recombination induced by replication fork collapse at the site-specific protein-DNA barrier RTS1 (Nguyen et al., 2015). Here, we provide evidence that efficient recruitment/retention of two key recombination proteins (Rad51 and Rad52) to RTS1 depends on unloading of the polymerase sliding clamp PCNA from DNA by Elg1. We also show that, in the absence of Elg1, reduced recombination is partially suppressed by deleting fbh1 or, to a lesser extent, srs2, which encode known anti-recombinogenic DNA helicases. These findings suggest that PCNA unloading by Elg1 is necessary to limit Fbh1 and Srs2 activity, and thereby enable recombination to proceed.
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Affiliation(s)
- Sanjeeta Tamang
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | | | - Carl A Morrow
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Fekret Osman
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Manisha Jalan
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Matthew C Whitby
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
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65
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Abstract
Genome replication involves dealing with obstacles that can result from DNA damage but also from chromatin alterations, topological stress, tightly bound proteins or non-B DNA structures such as R loops. Experimental evidence reveals that an engaged transcription machinery at the DNA can either enhance such obstacles or be an obstacle itself. Thus, transcription can become a potentially hazardous process promoting localized replication fork hindrance and stress, which would ultimately cause genome instability, a hallmark of cancer cells. Understanding the causes behind transcription-replication conflicts as well as how the cell resolves them to sustain genome integrity is the aim of this review.
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66
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Deegan TD, Baxter J, Ortiz Bazán MÁ, Yeeles JTP, Labib KPM. Pif1-Family Helicases Support Fork Convergence during DNA Replication Termination in Eukaryotes. Mol Cell 2019; 74:231-244.e9. [PMID: 30850330 PMCID: PMC6477153 DOI: 10.1016/j.molcel.2019.01.040] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 11/26/2018] [Accepted: 01/29/2019] [Indexed: 01/21/2023]
Abstract
The convergence of two DNA replication forks creates unique problems during DNA replication termination. In E. coli and SV40, the release of torsional strain by type II topoisomerases is critical for converging replisomes to complete DNA synthesis, but the pathways that mediate fork convergence in eukaryotes are unknown. We studied the convergence of reconstituted yeast replication forks that include all core replisome components and both type I and type II topoisomerases. We found that most converging forks stall at a very late stage, indicating a role for additional factors. We showed that the Pif1 and Rrm3 DNA helicases promote efficient fork convergence and completion of DNA synthesis, even in the absence of type II topoisomerase. Furthermore, Rrm3 and Pif1 are also important for termination of plasmid DNA replication in vivo. These findings identify a eukaryotic pathway for DNA replication termination that is distinct from previously characterized prokaryotic mechanisms.
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Affiliation(s)
- Tom D Deegan
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
| | - Jonathan Baxter
- Genome Damage and Stability Centre, Department of Life Sciences, University of Sussex, Brighton BN1 9RQ, UK
| | - María Ángeles Ortiz Bazán
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Joseph T P Yeeles
- The MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Karim P M Labib
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
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67
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tRNA Genes Affect Chromosome Structure and Function via Local Effects. Mol Cell Biol 2019; 39:MCB.00432-18. [PMID: 30718362 DOI: 10.1128/mcb.00432-18] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 01/18/2019] [Indexed: 11/20/2022] Open
Abstract
The genome is packaged and organized in an ordered, nonrandom manner, and specific chromatin segments contact nuclear substructures to mediate this organization. tRNA genes (tDNAs) are binding sites for transcription factors and architectural proteins and are thought to play an important role in the organization of the genome. In this study, we investigate the roles of tDNAs in genomic organization and chromosome function by editing a chromosome so that it lacked any tDNAs. Surprisingly our analyses of this tDNA-less chromosome show that loss of tDNAs does not grossly affect chromatin architecture or chromosome tethering and mobility. However, loss of tDNAs affects local nucleosome positioning and the binding of SMC proteins at these loci. The absence of tDNAs also leads to changes in centromere clustering and a reduction in the frequency of long-range HML-HMR heterochromatin clustering with concomitant effects on gene silencing. We propose that the tDNAs primarily affect local chromatin structure, which results in effects on long-range chromosome architecture.
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68
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Laflamme G, Sim S, Leary A, Pascariu M, Vogel J, D’Amours D. Interphase Microtubules Safeguard Mitotic Progression by Suppressing an Aurora B-Dependent Arrest Induced by DNA Replication Stress. Cell Rep 2019; 26:2875-2889.e3. [DOI: 10.1016/j.celrep.2019.02.051] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 12/21/2018] [Accepted: 02/13/2019] [Indexed: 10/27/2022] Open
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69
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DNA Replication Through Strand Displacement During Lagging Strand DNA Synthesis in Saccharomyces cerevisiae. Genes (Basel) 2019; 10:genes10020167. [PMID: 30795600 PMCID: PMC6409922 DOI: 10.3390/genes10020167] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 02/14/2019] [Accepted: 02/18/2019] [Indexed: 01/21/2023] Open
Abstract
This review discusses a set of experimental results that support the existence of extended strand displacement events during budding yeast lagging strand DNA synthesis. Starting from introducing the mechanisms and factors involved in leading and lagging strand DNA synthesis and some aspects of the architecture of the eukaryotic replisome, we discuss studies on bacterial, bacteriophage and viral DNA polymerases with potent strand displacement activities. We describe proposed pathways of Okazaki fragment processing via short and long flaps, with a focus on experimental results obtained in Saccharomyces cerevisiae that suggest the existence of frequent and extended strand displacement events during eukaryotic lagging strand DNA synthesis, and comment on their implications for genome integrity.
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70
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Jalan M, Oehler J, Morrow CA, Osman F, Whitby MC. Factors affecting template switch recombination associated with restarted DNA replication. eLife 2019; 8:41697. [PMID: 30667359 PMCID: PMC6358216 DOI: 10.7554/elife.41697] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 01/21/2019] [Indexed: 12/19/2022] Open
Abstract
Homologous recombination helps ensure the timely completion of genome duplication by restarting collapsed replication forks. However, this beneficial function is not without risk as replication restarted by homologous recombination is prone to template switching (TS) that can generate deleterious genome rearrangements associated with diseases such as cancer. Previously we established an assay for studying TS in Schizosaccharomyces pombe (Nguyen et al., 2015). Here, we show that TS is detected up to 75 kb downstream of a collapsed replication fork and can be triggered by head-on collision between the restarted fork and RNA Polymerase III transcription. The Pif1 DNA helicase, Pfh1, promotes efficient restart and also suppresses TS. A further three conserved helicases (Fbh1, Rqh1 and Srs2) strongly suppress TS, but there is no change in TS frequency in cells lacking Fml1 or Mus81. We discuss how these factors likely influence TS.
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Affiliation(s)
- Manisha Jalan
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Judith Oehler
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Carl A Morrow
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Fekret Osman
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Matthew C Whitby
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
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71
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Two Pif1 Family DNA Helicases Cooperate in Centromere Replication and Segregation in Saccharomyces cerevisiae. Genetics 2018; 211:105-119. [PMID: 30442759 PMCID: PMC6325707 DOI: 10.1534/genetics.118.301710] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 11/06/2018] [Indexed: 02/07/2023] Open
Abstract
Pif1 family helicases are found in virtually all eukaryotes. Saccharomyces cerevisiae (Sc) encodes two Pif1 family helicases, ScPif1 and Rrm3 ScPif1 is multifunctional, required not only for maintenance of mitochondrial DNA but also for multiple distinct nuclear functions. Rrm3 moves with the replication fork and promotes movement of the fork through ∼1400 hard-to-replicate sites, including centromeres. Here we show that ScPif1, like Rrm3, bound robustly to yeast centromeres but only if the centromere was active. While Rrm3 binding to centromeres occurred in early to mid S phase, about the same time as centromere replication, ScPif1 binding occurred later in the cell cycle when replication of most centromeres is complete. However, the timing of Rrm3 and ScPif1 centromere binding was altered by the absence of the other helicase, such that Rrm3 centromere binding occurred later in pif1-m2 cells and ScPif1 centromere binding occurred earlier in rrm3Δ cells. As shown previously, the modest pausing of replication forks at centromeres seen in wild-type cells was increased in the absence of Rrm3 While a lack of ScPif1 did not result in increased fork pausing at centromeres, pausing was even higher in rrm3Δ pif1Δ cells than in rrm3Δ cells. Likewise, centromere function as monitored by the loss rate of a centromere plasmid was increased in rrm3Δ but not pif1Δ cells, and was even higher in rrm3Δ pif1Δ cells than in rrm3Δ cells. Thus, ScPif1 promotes centromere replication and segregation, but only in the absence of Rrm3 These data also hint at a potential post-S phase function for ScPif1 at centromeres. These studies add to the growing list of ScPif1 functions that promote chromosome stability.
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72
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Geronimo CL, Singh SP, Galletto R, Zakian VA. The signature motif of the Saccharomyces cerevisiae Pif1 DNA helicase is essential in vivo for mitochondrial and nuclear functions and in vitro for ATPase activity. Nucleic Acids Res 2018; 46:8357-8370. [PMID: 30239884 PMCID: PMC6144861 DOI: 10.1093/nar/gky655] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 06/18/2018] [Accepted: 07/13/2018] [Indexed: 12/15/2022] Open
Abstract
Pif1 family DNA helicases are conserved from bacteria to humans and have critical and diverse functions in vivo that promote genome integrity. Pif1 family helicases share a 23 amino acid region, called the Pif1 signature motif (SM) that is unique to this family. To determine the importance of the SM, we did mutational and functional analysis of the SM from the Saccharomyces cerevisiae Pif1 (ScPif1). The mutations deleted portions of the SM, made one or multiple single amino acid changes in the SM, replaced the SM with its counterpart from a bacterial Pif1 family helicase and substituted an α-helical domain from another helicase for the part of the SM that forms an α helix. Mutants were tested for maintenance of mitochondrial DNA, inhibition of telomerase at telomeres and double strand breaks, and promotion of Okazaki fragment maturation. Although certain single amino acid changes in the SM can be tolerated, the presence and sequence of the ScPif1 SM were essential for all tested in vivo functions. Consistent with the in vivo analyses, in vitro studies showed that the presence and sequence of the ScPif1 SM were critical for ATPase activity but not substrate binding.
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Affiliation(s)
- Carly L Geronimo
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014, USA
| | - Saurabh P Singh
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Roberto Galletto
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Virginia A Zakian
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014, USA
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73
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Mohammad JB, Wallgren M, Sabouri N. The Pif1 signature motif of Pfh1 is necessary for both protein displacement and helicase unwinding activities, but is dispensable for strand-annealing activity. Nucleic Acids Res 2018; 46:8516-8531. [PMID: 30053106 PMCID: PMC6144812 DOI: 10.1093/nar/gky654] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 07/08/2018] [Accepted: 07/10/2018] [Indexed: 01/14/2023] Open
Abstract
Pfh1, the sole member of the Pif1 helicases in Schizosaccharomyces pombe, is multifunctional and essential for maintenance of both the nuclear and mitochondrial genomes. However, we lack mechanistic insights into the functions of Pfh1 and its different motifs. This paper is specifically concerned with the importance of the Pif1 signature motif (SM), a 23 amino acids motif unique to Pif1 helicases, because a single amino acid substitution in this motif is associated with increased risk of breast cancer in humans and inviability in S. pombe. Here we show that the nuclear isoform of Pfh1 (nPfh1) unwound RNA/DNA hybrids more efficiently than DNA/DNA, suggesting that Pfh1 resolves RNA/DNA structures like R-loops in vivo. In addition, nPfh1 displaced proteins from DNA and possessed strand-annealing activity. The unwinding and protein displacement activities were dependent on the SM because nPfh1 without a large portion of this motif (nPfh1-Δ21) or with the disease/inviability-linked mutation (nPfh1-L430P) lost these properties. Unexpectedly, both nPfh1-L430P and nPfh1-Δ21 still displayed binding to G-quadruplex DNA and demonstrated strand-annealing activity. Misregulated strand annealing and binding of nPfh1-L430P without unwinding are perhaps the reasons that cells expressing this allele are inviable.
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Affiliation(s)
- Jani B Mohammad
- Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden
| | - Marcus Wallgren
- Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden
| | - Nasim Sabouri
- Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden
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74
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The Main Role of Srs2 in DNA Repair Depends on Its Helicase Activity, Rather than on Its Interactions with PCNA or Rad51. mBio 2018; 9:mBio.01192-18. [PMID: 30018112 PMCID: PMC6050964 DOI: 10.1128/mbio.01192-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Homologous recombination (HR) is a mechanism that repairs a variety of DNA lesions. Under certain circumstances, however, HR can generate intermediates that can interfere with other cellular processes such as DNA transcription or replication. Cells have therefore developed pathways that abolish undesirable HR intermediates. The Saccharomyces cerevisiae yeast Srs2 helicase has a major role in one of these pathways. Srs2 also works during DNA replication and interacts with the clamp PCNA. The relative importance of Srs2’s helicase activity, Rad51 removal function, and PCNA interaction in genome stability remains unclear. We created a new SRS2 allele [srs2(1-850)] that lacks the whole C terminus, containing the interaction site for Rad51 and PCNA and interactions with many other proteins. Thus, the new allele encodes an Srs2 protein bearing only the activity of the DNA helicase. We find that the interactions of Srs2 with Rad51 and PCNA are dispensable for the main role of Srs2 in the repair of DNA damage in vegetative cells and for proper completion of meiosis. On the other hand, it has been shown that in cells impaired for the DNA damage tolerance (DDT) pathways, Srs2 generates toxic intermediates that lead to DNA damage sensitivity; we show that this negative Srs2 activity requires the C terminus of Srs2. Dissection of the genetic interactions of the srs2(1-850) allele suggest a role for Srs2’s helicase activity in sister chromatid cohesion. Our results also indicate that Srs2’s function becomes more central in diploid cells. Homologous recombination (HR) is a key mechanism that repairs damaged DNA. However, this process has to be tightly regulated; failure to regulate it can lead to genome instability. The Srs2 helicase is considered a regulator of HR; it was shown to be able to evict the recombinase Rad51 from DNA. Cells lacking Srs2 exhibit sensitivity to DNA-damaging agents, and in some cases, they display defects in DNA replication. The relative roles of the helicase and Rad51 removal activities of Srs2 in genome stability remain unclear. To address this question, we created a new Srs2 mutant which has only the DNA helicase domain. Our study shows that only the DNA helicase domain is needed to deal with DNA damage and assist in DNA replication during vegetative growth and in meiosis. Thus, our findings shift the view on the role of Srs2 in the maintenance of genome integrity.
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75
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Abstract
The spatiotemporal organization of chromatin plays central roles in cellular function. The ribosomal DNA (rDNA) chromatin undergoes dynamic structural changes during mitosis and stress. Here, we developed a CRISPR-based imaging system and tracked the condensation dynamics of rDNA chromatin in live yeast cells under glucose starvation. We found that acute glucose starvation triggers rapid condensation of rDNA. Time-lapse microscopy revealed two stages for rDNA condensation: a “primary stage,” when relaxed rDNA chromatin forms higher order loops or rings, and a “secondary stage,” when the rDNA rings further condense into compact clusters. Twisting of rDNA rings accompanies the secondary stage. The condensin complex, but not the cohesin complex, is required for efficient rDNA condensation in response to glucose starvation. Furthermore, we found that the DNA helicase Sgs1 is essential for the survival of cells expressing rDNA-bound dCas9, suggesting a role for helicases in facilitating DNA replication at dCas9-binding sites. A CRISPR-based imaging system allows tracking of rDNA condensation in single cells Glucose starvation triggers rDNA condensation in two prominent stages Condensin contributes to efficient rDNA condensation caused by glucose starvation Sgs1 helicase is required for normal rDNA replication at dCas9-binding sites
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Affiliation(s)
- Yuan Xue
- Department of Molecular Cellular and Developmental Biology, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
| | - Murat Acar
- Department of Molecular Cellular and Developmental Biology, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
- Department of Physics, Yale University, 217 Prospect Street, New Haven, CT 06511, USA
- Corresponding author
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76
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Simoneau A, Ricard É, Wurtele H. An interplay between multiple sirtuins promotes completion of DNA replication in cells with short telomeres. PLoS Genet 2018; 14:e1007356. [PMID: 29659581 PMCID: PMC5919697 DOI: 10.1371/journal.pgen.1007356] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 04/26/2018] [Accepted: 04/09/2018] [Indexed: 01/08/2023] Open
Abstract
The evolutionarily-conserved sirtuin family of histone deacetylases regulates a multitude of DNA-associated processes. A recent genome-wide screen conducted in the yeast Saccharomyces cerevisiae identified Yku70/80, which regulate nonhomologous end-joining (NHEJ) and telomere structure, as being essential for cell proliferation in the presence of the pan-sirtuin inhibitor nicotinamide (NAM). Here, we show that sirtuin-dependent deacetylation of both histone H3 lysine 56 and H4 lysine 16 promotes growth of yku70Δ and yku80Δ cells, and that the NAM sensitivity of these mutants is not caused by defects in DNA double-strand break repair by NHEJ, but rather by their inability to maintain normal telomere length. Indeed, our results indicate that in the absence of sirtuin activity, cells with abnormally short telomeres, e.g., yku70/80Δ or est1/2Δ mutants, present striking defects in S phase progression. Our data further suggest that early firing of replication origins at short telomeres compromises the cellular response to NAM- and genotoxin-induced replicative stress. Finally, we show that reducing H4K16ac in yku70Δ cells limits activation of the DNA damage checkpoint kinase Rad53 in response to replicative stress, which promotes usage of translesion synthesis and S phase progression. Our results reveal a novel interplay between sirtuin-mediated regulation of chromatin structure and telomere-regulating factors in promoting timely completion of S phase upon replicative stress.
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Affiliation(s)
- Antoine Simoneau
- Centre de recherche de l’Hôpital Maisonneuve-Rosemont, boulevard de l’Assomption, Montréal, Canada
- Programme de Biologie Moléculaire, Université de Montréal, Montréal, Canada
| | - Étienne Ricard
- Centre de recherche de l’Hôpital Maisonneuve-Rosemont, boulevard de l’Assomption, Montréal, Canada
- Programme de Biologie Moléculaire, Université de Montréal, Montréal, Canada
| | - Hugo Wurtele
- Centre de recherche de l’Hôpital Maisonneuve-Rosemont, boulevard de l’Assomption, Montréal, Canada
- Département de Médecine, Université de Montréal, Montréal, Canada
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77
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García-Rodríguez N, Morawska M, Wong RP, Daigaku Y, Ulrich HD. Spatial separation between replisome- and template-induced replication stress signaling. EMBO J 2018; 37:embj.201798369. [PMID: 29581097 PMCID: PMC5920239 DOI: 10.15252/embj.201798369] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Revised: 01/29/2018] [Accepted: 02/26/2018] [Indexed: 11/09/2022] Open
Abstract
Polymerase‐blocking DNA lesions are thought to elicit a checkpoint response via accumulation of single‐stranded DNA at stalled replication forks. However, as an alternative to persistent fork stalling, re‐priming downstream of lesions can give rise to daughter‐strand gaps behind replication forks. We show here that the processing of such structures by an exonuclease, Exo1, is required for timely checkpoint activation, which in turn prevents further gap erosion in S phase. This Rad9‐dependent mechanism of damage signaling is distinct from the Mrc1‐dependent, fork‐associated response to replication stress induced by conditions such as nucleotide depletion or replisome‐inherent problems, but reminiscent of replication‐independent checkpoint activation by single‐stranded DNA. Our results indicate that while replisome stalling triggers a checkpoint response directly at the stalled replication fork, the response to replication stress elicited by polymerase‐blocking lesions mainly emanates from Exo1‐processed, postreplicative daughter‐strand gaps, thus offering a mechanistic explanation for the dichotomy between replisome‐ versus template‐induced checkpoint signaling.
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Affiliation(s)
| | - Magdalena Morawska
- Institute of Molecular Biology (IMB), Mainz, Germany.,Cancer Research UK London Research Institute, Clare Hall Laboratories, Blanche Lane South Mimms, UK
| | - Ronald P Wong
- Institute of Molecular Biology (IMB), Mainz, Germany
| | - Yasukazu Daigaku
- Cancer Research UK London Research Institute, Clare Hall Laboratories, Blanche Lane South Mimms, UK
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78
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Andis NM, Sausen CW, Alladin A, Bochman ML. The WYL Domain of the PIF1 Helicase from the Thermophilic Bacterium Thermotoga elfii is an Accessory Single-Stranded DNA Binding Module. Biochemistry 2018; 57:1108-1118. [PMID: 29341597 DOI: 10.1021/acs.biochem.7b01233] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PIF1 family helicases are conserved from bacteria to man. With the exception of the well-studied yeast PIF1 helicases (e.g., ScPif1 and ScRrm3), however, very little is known about how these enzymes help maintain genome stability. Indeed, we lack a basic understanding of the protein domains found N- and C-terminal to the characteristic central PIF1 helicase domain in these proteins. Here, using chimeric constructs, we show that the ScPif1 and ScRrm3 helicase domains are interchangeable and that the N-terminus of ScRrm3 is important for its function in vivo. This suggests that PIF1 family helicases evolved functional modules fused to a generic motor domain. To investigate this hypothesis, we characterized the biochemical activities of the PIF1 helicase from the thermophilic bacterium Thermotoga elfii (TePif1), which contains a C-terminal WYL domain of unknown function. Like helicases from other thermophiles, recombinant TePif1 was easily prepared, thermostable in vitro, and displayed activities similar to its eukaryotic homologues. We also found that the WYL domain was necessary for high-affinity single-stranded DNA (ssDNA) binding and affected both ATPase and helicase activities. Deleting the WYL domain from TePif1 or mutating conserved residues in the predicted ssDNA binding site uncoupled ATPase activity and DNA unwinding, leading to higher rates of ATP hydrolysis but less efficient DNA helicase activity. Our findings suggest that the domains of unknown function found in eukaryotic PIF1 helicases may also confer functional specificity and additional activities to these enzymes, which should be investigated in future work.
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Affiliation(s)
- Nicholas M Andis
- Molecular and Cellular Biochemistry Department, Indiana University , Bloomington, Indiana 47405, United States
| | - Christopher W Sausen
- Molecular and Cellular Biochemistry Department, Indiana University , Bloomington, Indiana 47405, United States
| | - Ashna Alladin
- Molecular and Cellular Biochemistry Department, Indiana University , Bloomington, Indiana 47405, United States
| | - Matthew L Bochman
- Molecular and Cellular Biochemistry Department, Indiana University , Bloomington, Indiana 47405, United States
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79
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Peng XP, Lim S, Li S, Marjavaara L, Chabes A, Zhao X. Acute Smc5/6 depletion reveals its primary role in rDNA replication by restraining recombination at fork pausing sites. PLoS Genet 2018; 14:e1007129. [PMID: 29360860 PMCID: PMC5779651 DOI: 10.1371/journal.pgen.1007129] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Accepted: 11/27/2017] [Indexed: 11/18/2022] Open
Abstract
Smc5/6, a member of the conserved SMC family of complexes, is essential for growth in most organisms. Its exact functions in a mitotic cell cycle are controversial, as chronic Smc5/6 loss-of-function alleles produce varying phenotypes. To circumvent this issue, we acutely depleted Smc5/6 in budding yeast and determined the first cell cycle consequences of Smc5/6 removal. We found a striking primary defect in replication of the ribosomal DNA (rDNA) array. Each rDNA repeat contains a programmed replication fork barrier (RFB) established by the Fob1 protein. Fob1 removal improves rDNA replication in Smc5/6 depleted cells, implicating Smc5/6 in the management of programmed fork pausing. A similar improvement is achieved by removing the DNA helicase Mph1 whose recombinogenic activity can be inhibited by Smc5/6 under DNA damage conditions. DNA 2D gel analyses further show that Smc5/6 loss increases recombination structures at RFB regions; moreover, mph1∆ and fob1∆ similarly reduce this accumulation. These findings point to an important mitotic role for Smc5/6 in restraining recombination events when protein barriers in rDNA stall replication forks. As rDNA maintenance influences multiple essential cellular processes, Smc5/6 likely links rDNA stability to overall mitotic growth. Smc5/6 belongs to the SMC (Structural Maintenance of Chromosomes) family of protein complexes, all of which are highly conserved and critical for genome maintenance. To address the roles of Smc5/6 during growth, we rapidly depleted its subunits in yeast and found the main acute effect to be defective ribosomal DNA (rDNA) duplication. The rDNA contains hundreds of sites that can pause replication forks; these must be carefully managed for cells to finish replication. We found that reducing fork pausing improved rDNA replication in cells without Smc5/6. Further analysis suggested that Smc5/6 prevents the DNA helicase Mph1 from turning paused forks into recombination structures, which cannot be processed without Smc5/6. Our findings thus revealed a key role for Smc5/6 in managing endogenous replication fork pausing. As rDNA and its associated nucleolar structure are critical for overall genome maintenance and other cellular processes, rDNA regulation by Smc5/6 would be expected to have multilayered effects on cell physiology and growth.
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Affiliation(s)
- Xiao P. Peng
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY, United States of America
- Tri-Institutional MD-PhD Program of Weill Cornell Medical School, Rockefeller University, and Sloan-Kettering Cancer Center, New York, NY, United States of America
| | - Shelly Lim
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY, United States of America
| | - Shibai Li
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY, United States of America
| | - Lisette Marjavaara
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Andrei Chabes
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Xiaolan Zhao
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY, United States of America
- * E-mail:
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80
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Shukla A, Bhargava P. Regulation of tRNA gene transcription by the chromatin structure and nucleosome dynamics. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2017; 1861:295-309. [PMID: 29313808 DOI: 10.1016/j.bbagrm.2017.11.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Revised: 11/27/2017] [Accepted: 11/27/2017] [Indexed: 01/19/2023]
Abstract
The short, non-coding genes transcribed by the RNA polymerase (pol) III, necessary for survival of a cell, need to be repressed under the stress conditions in vivo. The pol III-transcribed genes have adopted several novel chromatin-based regulatory mechanisms to their advantage. In the budding yeast, the sub-nucleosomal size tRNA genes are found in the nucleosome-free regions, flanked by positioned nucleosomes at both the ends. With their chromosomes-wide distribution, all tRNA genes have a different chromatin context. A single nucleosome dynamics controls the accessibility of the genes for transcription. This dynamics operates under the influence of several chromatin modifiers in a gene-specific manner, giving the scope for differential regulation of even the isogenes within a tRNA gene family. The chromatin structure around the pol III-transcribed genes provides a context conducive for steady-state transcription as well as gene-specific transcriptional regulation upon signaling from the environmental cues. This article is part of a Special Issue entitled: SI: Regulation of tRNA synthesis and modification in physiological conditions and disease edited by Dr. Boguta Magdalena.
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Affiliation(s)
- Ashutosh Shukla
- Centre for Cellular and Molecular Biology (Council of Scientific and Industrial Research), Uppal Road, Hyderabad 500007, India
| | - Purnima Bhargava
- Centre for Cellular and Molecular Biology (Council of Scientific and Industrial Research), Uppal Road, Hyderabad 500007, India.
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81
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Cabral M, Cheng X, Singh S, Ivessa AS. Absence of Non-histone Protein Complexes at Natural Chromosomal Pause Sites Results in Reduced Replication Pausing in Aging Yeast Cells. Cell Rep 2017; 17:1747-1754. [PMID: 27829146 DOI: 10.1016/j.celrep.2016.10.050] [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] [Received: 05/24/2016] [Revised: 09/08/2016] [Accepted: 10/14/2016] [Indexed: 11/26/2022] Open
Abstract
There is substantial evidence that genomic instability increases during aging. Replication pausing (and stalling) at difficult-to-replicate chromosomal sites may induce genomic instability. Interestingly, in aging yeast cells, we observed reduced replication pausing at various natural replication pause sites (RPSs) in ribosomal DNA (rDNA) and non-rDNA locations (e.g., silent replication origins and tRNA genes). The reduced pausing occurs independent of the DNA helicase Rrm3p, which facilitates replication past these non-histone protein-complex-bound RPSs, and is independent of the deacetylase Sir2p. Conditions of caloric restriction (CR), which extend life span, also cause reduced replication pausing at the 5S rDNA and at tRNA genes. In aged and CR cells, the RPSs are less occupied by their specific non-histone protein complexes (e.g., the preinitiation complex TFIIIC), likely because members of these complexes have primarily cytosolic localization. These conditions may lead to reduced replication pausing and may lower replication stress at these sites during aging.
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Affiliation(s)
- Marleny Cabral
- Department of Cell Biology and Molecular Medicine, Rutgers New Jersey Medical School, Rutgers Biomedical and Health Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA
| | - Xin Cheng
- Department of Cell Biology and Molecular Medicine, Rutgers New Jersey Medical School, Rutgers Biomedical and Health Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA
| | - Sukhwinder Singh
- Pathology and Laboratory Medicine/Flow Cytometry and Immunology Core Laboratory, Rutgers New Jersey Medical School, Rutgers Biomedical and Health Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA
| | - Andreas S Ivessa
- Department of Cell Biology and Molecular Medicine, Rutgers New Jersey Medical School, Rutgers Biomedical and Health Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA.
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82
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Zhang Q, Bassetti F, Gherardi M, Lagomarsino MC. Cell-to-cell variability and robustness in S-phase duration from genome replication kinetics. Nucleic Acids Res 2017; 45:8190-8198. [PMID: 28854733 PMCID: PMC5737480 DOI: 10.1093/nar/gkx556] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 06/19/2017] [Indexed: 11/13/2022] Open
Abstract
Genome replication, a key process for a cell, relies on stochastic initiation by replication origins, causing a variability of replication timing from cell to cell. While stochastic models of eukaryotic replication are widely available, the link between the key parameters and overall replication timing has not been addressed systematically. We use a combined analytical and computational approach to calculate how positions and strength of many origins lead to a given cell-to-cell variability of total duration of the replication of a large region, a chromosome or the entire genome. Specifically, the total replication timing can be framed as an extreme-value problem, since it is due to the last region that replicates in each cell. Our calculations identify two regimes based on the spread between characteristic completion times of all inter-origin regions of a genome. For widely different completion times, timing is set by the single specific region that is typically the last to replicate in all cells. Conversely, when the completion time of all regions are comparable, an extreme-value estimate shows that the cell-to-cell variability of genome replication timing has universal properties. Comparison with available data shows that the replication program of three yeast species falls in this extreme-value regime.
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Affiliation(s)
- Qing Zhang
- Sorbonne Universités, UPMC Univ Paris 06, UMR 7238, Computational and Quantitative Biology, 4 Place Jussieu, Paris, France
| | | | - Marco Gherardi
- Sorbonne Universités, UPMC Univ Paris 06, UMR 7238, Computational and Quantitative Biology, 4 Place Jussieu, Paris, France.,IFOM, FIRC Institute of Molecular Oncology, Milan, Italy
| | - Marco Cosentino Lagomarsino
- Sorbonne Universités, UPMC Univ Paris 06, UMR 7238, Computational and Quantitative Biology, 4 Place Jussieu, Paris, France.,IFOM, FIRC Institute of Molecular Oncology, Milan, Italy.,CNRS, UMR 7238, Paris, France
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83
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Lin X, Wei F, Whyte P, Tang D. BMI1 reduces ATR activation and signalling caused by hydroxyurea. Oncotarget 2017; 8:89707-89721. [PMID: 29163782 PMCID: PMC5685703 DOI: 10.18632/oncotarget.21111] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 09/03/2017] [Indexed: 01/31/2023] Open
Abstract
BMI1 facilitates DNA damage response (DDR) induced by double strand DNA breaks; however, it remains unknown whether BMI1 functions in single strand DNA (ssDNA) lesions-initiated DDR. We report here that BMI1 reduces hydroxyurea-elicited ATR activation, thereby reducing the S-phase checkpoints. Hydroxyurea induces ssDNA lesions, which activate ATR through binding TOPBP1 as evidenced by phosphorylation of ATR at threonine 1989 (ATRpT1989). ATR subsequently phosphorylates H2AX at serine 139 (γH2AX) and CHK1 at serine 345 (CHK1pS345), leading to phosphorylation of CDK1 at tyrosine 15 (CDK1pY15) and S-phase arrest. BMI1 overexpression reduced γH2AX, CHK1pS345, CDK1pY15, S-phase arrest, and ATR activation in HU-treated MCF7 and DU145 cells, whereas BMI1 knockdown enhanced these events. BMI1 contains a ring finger, helix-turn, proline/serine domain and two nuclear localization signals (NLS). Individual deletion of these domains did not abolish BMI1-derived reductions of CHK1pS345 in MCF7 cells following HU exposure, suggesting that these structural features are not essential for BMI1 to attenuate ATR-mediated CHK1pS345. BMI1 interacts with both TOPBP1 and ATR. Furthermore, all of our BMI1 mutants associate with endogenous TOPBP1. It has previously been established that association of TOPBP1 and ATR is required for ATR activation. Thus, our results suggest that BMI1 decreases ATR activation through a mechanism that involves binding to TOPBP1 and/or ATR.
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Affiliation(s)
- Xiaozeng Lin
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.,Father Sean O'Sullivan Research Institute, Hamilton, Ontario, Canada.,The Hamilton Center for Kidney Research, St. Joseph's Hospital, Hamilton, Ontario, Canada
| | - Fengxiang Wei
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.,Father Sean O'Sullivan Research Institute, Hamilton, Ontario, Canada.,The Hamilton Center for Kidney Research, St. Joseph's Hospital, Hamilton, Ontario, Canada.,The Genetics Laboratory, Longgang District Maternity and Child Healthcare Hospital, Longgang District, Shenzhen, Guangdong, P.R. China
| | - Peter Whyte
- Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Damu Tang
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.,Father Sean O'Sullivan Research Institute, Hamilton, Ontario, Canada.,The Hamilton Center for Kidney Research, St. Joseph's Hospital, Hamilton, Ontario, Canada
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84
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Structure and function of Pif1 helicase. Biochem Soc Trans 2017; 45:1159-1171. [PMID: 28900015 DOI: 10.1042/bst20170096] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 08/10/2017] [Accepted: 08/11/2017] [Indexed: 12/18/2022]
Abstract
Pif1 family helicases have multiple roles in the maintenance of nuclear and mitochondrial DNA in eukaryotes. Saccharomyces cerevisiae Pif1 is involved in replication through barriers to replication, such as G-quadruplexes and protein blocks, and reduces genetic instability at these sites. Another Pif1 family helicase in S. cerevisiae, Rrm3, assists in fork progression through replication fork barriers at the rDNA locus and tRNA genes. ScPif1 (Saccharomyces cerevisiae Pif1) also negatively regulates telomerase, facilitates Okazaki fragment processing, and acts with polymerase δ in break-induced repair. Recent crystal structures of bacterial Pif1 helicases and the helicase domain of human PIF1 combined with several biochemical and biological studies on the activities of Pif1 helicases have increased our understanding of the function of these proteins. This review article focuses on these structures and the mechanism(s) proposed for Pif1's various activities on DNA.
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85
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Nguyen JHG, Viterbo D, Anand RP, Verra L, Sloan L, Richard GF, Freudenreich CH. Differential requirement of Srs2 helicase and Rad51 displacement activities in replication of hairpin-forming CAG/CTG repeats. Nucleic Acids Res 2017; 45:4519-4531. [PMID: 28175398 PMCID: PMC5416882 DOI: 10.1093/nar/gkx088] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 01/31/2017] [Indexed: 12/25/2022] Open
Abstract
Trinucleotide repeats are a source of genome instability, causing replication fork stalling, chromosome fragility, and impaired repair. Specialized helicases play an important role in unwinding DNA structures to maintain genome stability. The Srs2 helicase unwinds DNA hairpins, facilitates replication, and prevents repeat instability and fragility. However, since Srs2 is a multifunctional protein with helicase activity and the ability to displace Rad51 recombinase, it was unclear which functions were required for its various protective roles. Here, using SRS2 separation-of-function alleles, we show that in the absence of Srs2 recruitment to PCNA or in helicase-deficient mutants, breakage at a CAG/CTG repeat increases. We conclude that Srs2 interaction with PCNA allows the helicase activity to unwind fork-blocking CAG/CTG hairpin structures to prevent breaks. Independently of PCNA binding, Srs2 also displaces Rad51 from nascent strands to prevent recombination-dependent repeat expansions and contractions. By 2D gel electrophoresis, we detect two different kinds of structured intermediates or joint molecules (JMs). Some JMs are Rad51-independent and exhibit properties of reversed forks, including being processed by the Exo1 nuclease. In addition, in a helicase-deficient mutant, Rad51-dependent JMs are detected, probably corresponding to recombination between sisters. These results clarify the many roles of Srs2 in facilitating replication through fork-blocking hairpin lesions.
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Affiliation(s)
| | - David Viterbo
- Institut Pasteur, Department Genomes & Genetics, CNRS, UMR3525, Université Pierre et Marie Curie, UFR927, 25 rue du Dr Roux, F-75015 Paris, France
| | - Ranjith P Anand
- Department of Biology, Tufts University, Medford, MA 02155, USA
| | - Lauren Verra
- Department of Biology, Tufts University, Medford, MA 02155, USA
| | - Laura Sloan
- Department of Biology, Tufts University, Medford, MA 02155, USA
| | - Guy-Franck Richard
- Institut Pasteur, Department Genomes & Genetics, CNRS, UMR3525, Université Pierre et Marie Curie, UFR927, 25 rue du Dr Roux, F-75015 Paris, France
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86
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Sasaki M, Kobayashi T. Ctf4 Prevents Genome Rearrangements by Suppressing DNA Double-Strand Break Formation and Its End Resection at Arrested Replication Forks. Mol Cell 2017; 66:533-545.e5. [PMID: 28525744 DOI: 10.1016/j.molcel.2017.04.020] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 03/20/2017] [Accepted: 04/26/2017] [Indexed: 12/19/2022]
Abstract
Arrested replication forks lead to DNA double-strand breaks (DSBs), which are a major source of genome rearrangements. Yet DSB repair in the context of broken forks remains poorly understood. Here we demonstrate that DSBs that are formed at arrested forks in the budding yeast ribosomal RNA gene (rDNA) locus are normally repaired by pathways dependent on the Mre11-Rad50-Xrs2 complex but independent of HR. HR is also dispensable for DSB repair at stalled forks at tRNA genes. In contrast, in cells lacking the core replisome component Ctf4, DSBs are formed more frequently, and these DSBs undergo end resection and HR-mediated repair that is prone to rDNA hyper-amplification; this highlights Ctf4 as a key regulator of DSB end resection at arrested forks. End resection also occurs during physiological rDNA amplification even in the presence of Ctf4. Suppression of end resection is thus important for protecting DSBs at arrested forks from chromosome rearrangements.
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MESH Headings
- DNA Breaks, Double-Stranded
- DNA Repair
- DNA Replication
- DNA, Fungal/biosynthesis
- DNA, Fungal/chemistry
- DNA, Fungal/genetics
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Endodeoxyribonucleases/genetics
- Endodeoxyribonucleases/metabolism
- Exodeoxyribonucleases/genetics
- Exodeoxyribonucleases/metabolism
- Gene Rearrangement
- Microbial Viability
- Mutation
- Nucleic Acid Conformation
- RNA, Fungal/genetics
- RNA, Fungal/metabolism
- RNA, Ribosomal/genetics
- RNA, Ribosomal/metabolism
- RNA, Transfer/genetics
- RNA, Transfer/metabolism
- Replication Origin
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins/genetics
- Saccharomyces cerevisiae Proteins/metabolism
- Time Factors
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Affiliation(s)
- Mariko Sasaki
- Laboratory of Genome Regeneration, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Takehiko Kobayashi
- Laboratory of Genome Regeneration, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
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87
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Rowlands H, Dhavarasa P, Cheng A, Yankulov K. Forks on the Run: Can the Stalling of DNA Replication Promote Epigenetic Changes? Front Genet 2017; 8:86. [PMID: 28690636 PMCID: PMC5479891 DOI: 10.3389/fgene.2017.00086] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 06/06/2017] [Indexed: 11/13/2022] Open
Abstract
Built of DNA polymerases and multiple associated factors, the replication fork steadily progresses along the DNA template and faithfully replicates DNA. This model can be found in practically every textbook of genetics, with the more complex situation of chromatinized DNA in eukaryotes often viewed as a variation. However, the replication-coupled disassembly/reassembly of chromatin adds significant complexity to the whole replication process. During the course of eukaryotic DNA replication the forks encounter various conditions and numerous impediments. These include nucleosomes with a variety of post-translational modifications, euchromatin and heterochromatin, differentially methylated DNA, tightly bound proteins, active gene promoters and DNA loops. At such positions the forks slow down or even stall. Dedicated factors stabilize the fork and prevent its rotation or collapse, while other factors resolve the replication block and facilitate the resumption of elongation. The fate of histones during replication stalling and resumption is not well understood. In this review we briefly describe recent advances in our understanding of histone turnover during DNA replication and focus on the possible mechanisms of nucleosome disassembly/reassembly at paused replication forks. We propose that replication pausing provides opportunities for an epigenetic change of the associated locus.
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Affiliation(s)
- Hollie Rowlands
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
| | - Piriththiv Dhavarasa
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
| | - Ashley Cheng
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
| | - Krassimir Yankulov
- Department of Molecular and Cellular Biology, University of Guelph, GuelphON, Canada
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88
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Puddu F, Salguero I, Herzog M, Geisler NJ, Costanzo V, Jackson SP. Chromatin determinants impart camptothecin sensitivity. EMBO Rep 2017; 18:1000-1012. [PMID: 28389464 PMCID: PMC5452016 DOI: 10.15252/embr.201643560] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 03/07/2017] [Accepted: 03/09/2017] [Indexed: 11/09/2022] Open
Abstract
Camptothecin-induced locking of topoisomerase 1 on DNA generates a physical barrier to replication fork progression and creates topological stress. By allowing replisome rotation, absence of the Tof1/Csm3 complex promotes the conversion of impending topological stress to DNA catenation and causes camptothecin hypersensitivity. Through synthetic viability screening, we discovered that histone H4 K16 deacetylation drives the sensitivity of yeast cells to camptothecin and that inactivation of this pathway by mutating H4 K16 or the genes SIR1-4 suppresses much of the hypersensitivity of tof1∆ strains towards this agent. We show that disruption of rDNA or telomeric silencing does not mediate camptothecin resistance but that disruption of Sir1-dependent chromatin domains is sufficient to suppress camptothecin sensitivity in wild-type and tof1∆ cells. We suggest that topoisomerase 1 inhibition in proximity of these domains causes topological stress that leads to DNA hypercatenation, especially in the absence of the Tof1/Csm3 complex. Finally, we provide evidence of the evolutionarily conservation of this mechanism.
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Affiliation(s)
- Fabio Puddu
- The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Israel Salguero
- The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Mareike Herzog
- The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge, UK
- The Wellcome Trust Sanger Institute, Hinxton Cambridge, UK
| | - Nicola J Geisler
- The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Vincenzo Costanzo
- IFOM (Fondazione Istituto FIRC di Oncologia Molecolare), Milan, Italy
| | - Stephen P Jackson
- The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge, UK
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89
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Abstract
The accurate and complete replication of genomic DNA is essential for all life. In eukaryotic cells, the assembly of the multi-enzyme replisomes that perform replication is divided into stages that occur at distinct phases of the cell cycle. Replicative DNA helicases are loaded around origins of DNA replication exclusively during G1 phase. The loaded helicases are then activated during S phase and associate with the replicative DNA polymerases and other accessory proteins. The function of the resulting replisomes is monitored by checkpoint proteins that protect arrested replisomes and inhibit new initiation when replication is inhibited. The replisome also coordinates nucleosome disassembly, assembly, and the establishment of sister chromatid cohesion. Finally, when two replisomes converge they are disassembled. Studies in Saccharomyces cerevisiae have led the way in our understanding of these processes. Here, we review our increasingly molecular understanding of these events and their regulation.
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90
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Wyse B, Oshidari R, Rowlands H, Abbasi S, Yankulov K. RRM3 regulates epigenetic conversions in Saccharomyces cerevisiae in conjunction with Chromatin Assembly Factor I. Nucleus 2017; 7:405-14. [PMID: 27645054 DOI: 10.1080/19491034.2016.1212796] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Chromatin structures are transmitted to daughter cells through a complex system of nucleosome disassembly and re-assembly at the advancing replication forks. However, the role of replication pausing in the transmission and perturbation of chromatin structures has not been addressed. RRM3 encodes a DNA helicase, which facilitates replication at sites covered with non-histone protein complexes (tRNA genes, active gene promoters, telomeres) in Saccharomyces cerevisiae. In this report we show that the deletion of RRM3 reduces the frequency of epigenetic conversions in the subtelomeric regions of the chromosomes. This phenotype is strongly dependent on 2 histone chaperones, CAF-I and ASF1, which are involved in the reassembly of nucleosomes behind replication forks, but not on the histone chaperone HIR1. We also show that the deletion of RRM3 increases the spontaneous mutation rates in conjunction with CAF-I and ASF1, but not HIR1. Finally, we demonstrate that Rrm3p and CAF-I compete for the binding to the DNA replication clamp PCNA (Proliferating Cell Nuclear Antigen). We propose that the stalling of DNA replication predisposes to epigenetic conversions and that RRM3 and CAF-I play key roles in this process.
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Affiliation(s)
- Brandon Wyse
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Roxanne Oshidari
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Hollie Rowlands
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Sanna Abbasi
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Krassimir Yankulov
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
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91
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Muñoz-Galván S, García-Rubio M, Ortega P, Ruiz JF, Jimeno S, Pardo B, Gómez-González B, Aguilera A. A new role for Rrm3 in repair of replication-born DNA breakage by sister chromatid recombination. PLoS Genet 2017; 13:e1006781. [PMID: 28475600 PMCID: PMC5438189 DOI: 10.1371/journal.pgen.1006781] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 05/19/2017] [Accepted: 04/26/2017] [Indexed: 11/19/2022] Open
Abstract
Replication forks stall at different DNA obstacles such as those originated by transcription. Fork stalling can lead to DNA double-strand breaks (DSBs) that will be preferentially repaired by homologous recombination when the sister chromatid is available. The Rrm3 helicase is a replisome component that promotes replication upon fork stalling, accumulates at highly transcribed regions and prevents not only transcription-induced replication fork stalling but also transcription-associated hyper-recombination. This led us to explore the possible role of Rrm3 in the repair of DSBs when originating at the passage of the replication fork. Using a mini-HO system that induces mainly single-stranded DNA breaks, we show that rrm3Δ cells are defective in DSB repair. The defect is clearly seen in sister chromatid recombination, the major repair pathway of replication-born DSBs. Our results indicate that Rrm3 recruitment to replication-born DSBs is crucial for viability, uncovering a new role for Rrm3 in the repair of broken replication forks. DNA replication needs to be precise to ensure cell survival and to avoid genetic instability. Different DNA obstacles, such as those originated by transcription, frequently hamper replication fork progression leading to fork stalling or even fork breakage. This requires the homologous recombination machinery to repair the damage. Here, we uncovered a role for yeast Rrm3, a replisome component known to promote replication upon fork stalling, in the repair of replication-born double strand breaks. In particular, rrm3Δ cells show a defect in the recombination with the sister chromatid, the preferred template for the maintenance of genome integrity. Our results support the possibility that the known accumulation of Rrm3 at sites of active transcription reflects an active role of Rrm3 in the repair of broken forks.
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Affiliation(s)
- Sandra Muñoz-Galván
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - María García-Rubio
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - Pedro Ortega
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - Jose F. Ruiz
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - Sonia Jimeno
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - Benjamin Pardo
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - Belén Gómez-González
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
- * E-mail: (AA); (BGG)
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
- * E-mail: (AA); (BGG)
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92
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Tran PLT, Pohl TJ, Chen CF, Chan A, Pott S, Zakian VA. PIF1 family DNA helicases suppress R-loop mediated genome instability at tRNA genes. Nat Commun 2017; 8:15025. [PMID: 28429714 PMCID: PMC5413955 DOI: 10.1038/ncomms15025] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 02/17/2017] [Indexed: 01/21/2023] Open
Abstract
Saccharomyces cerevisiae encodes two Pif1 family DNA helicases, Pif1 and Rrm3. Rrm3 promotes DNA replication past stable protein complexes at tRNA genes (tDNAs). We identify a new role for the Pif1 helicase: promotion of replication and suppression of DNA damage at tDNAs. Pif1 binds multiple tDNAs, and this binding is higher in rrm3Δ cells. Accumulation of replication intermediates and DNA damage at tDNAs is higher in pif1Δ rrm3Δ than in rrm3Δ cells. DNA damage at tDNAs in the absence of these helicases is suppressed by destabilizing R-loops while Pif1 and Rrm3 binding to tDNAs is increased upon R-loop stabilization. We propose that Rrm3 and Pif1 promote genome stability at tDNAs by displacing the stable multi-protein transcription complex and by removing R-loops. Thus, we identify tDNAs as a new source of R-loop-mediated DNA damage. Given their large number and high transcription rate, tDNAs may be a potent source of genome instability. The budding yeast genome encodes two Pif1 family helicases, Pif1 and Rrm3, previously shown to have distinct functions in the maintenance of telomeres and other aspects of genome stability. Here the authors identify a role for Pif1 (and Rrm3) in promoting DNA replication and suppressing R-loop mediated DNA damage at tRNA genes.
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Affiliation(s)
- Phong Lan Thao Tran
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, New Jersey 08544, USA
| | - Thomas J Pohl
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, New Jersey 08544, USA
| | - Chi-Fu Chen
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, New Jersey 08544, USA
| | - Angela Chan
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, New Jersey 08544, USA
| | - Sebastian Pott
- Department of Human Genetics, University of Chicago, 920 E 58th St, Chicago, Illinois 60637, USA
| | - Virginia A Zakian
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, New Jersey 08544, USA
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93
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Alterations in cellular metabolism triggered by URA7 or GLN3 inactivation cause imbalanced dNTP pools and increased mutagenesis. Proc Natl Acad Sci U S A 2017; 114:E4442-E4451. [PMID: 28416670 DOI: 10.1073/pnas.1618714114] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Eukaryotic DNA replication fidelity relies on the concerted action of DNA polymerase nucleotide selectivity, proofreading activity, and DNA mismatch repair (MMR). Nucleotide selectivity and proofreading are affected by the balance and concentration of deoxyribonucleotide (dNTP) pools, which are strictly regulated by ribonucleotide reductase (RNR). Mutations preventing DNA polymerase proofreading activity or MMR function cause mutator phenotypes and consequently increased cancer susceptibility. To identify genes not previously linked to high-fidelity DNA replication, we conducted a genome-wide screen in Saccharomyces cerevisiae using DNA polymerase active-site mutants as a "sensitized mutator background." Among the genes identified in our screen, three metabolism-related genes (GLN3, URA7, and SHM2) have not been previously associated to the suppression of mutations. Loss of either the transcription factor Gln3 or inactivation of the CTP synthetase Ura7 both resulted in the activation of the DNA damage response and imbalanced dNTP pools. Importantly, these dNTP imbalances are strongly mutagenic in genetic backgrounds where DNA polymerase function or MMR activity is partially compromised. Previous reports have shown that dNTP pool imbalances can be caused by mutations altering the allosteric regulation of enzymes involved in dNTP biosynthesis (e.g., RNR or dCMP deaminase). Here, we provide evidence that mutations affecting genes involved in RNR substrate production can cause dNTP imbalances, which cannot be compensated by RNR or other enzymatic activities. Moreover, Gln3 inactivation links nutrient deprivation to increased mutagenesis. Our results suggest that similar genetic interactions could drive mutator phenotypes in cancer cells.
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94
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Myka KK, Hawkins M, Syeda AH, Gupta MK, Meharg C, Dillingham MS, Savery NJ, Lloyd RG, McGlynn P. Inhibiting translation elongation can aid genome duplication in Escherichia coli. Nucleic Acids Res 2017; 45:2571-2584. [PMID: 27956500 PMCID: PMC5389703 DOI: 10.1093/nar/gkw1254] [Citation(s) in RCA: 10] [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: 08/22/2016] [Revised: 11/28/2016] [Accepted: 12/01/2016] [Indexed: 12/28/2022] Open
Abstract
Conflicts between replication and transcription challenge chromosome duplication. Escherichia coli replisome movement along transcribed DNA is promoted by Rep and UvrD accessory helicases with Δrep ΔuvrD cells being inviable under rapid growth conditions. We have discovered that mutations in a tRNA gene, aspT, in an aminoacyl tRNA synthetase, AspRS, and in a translation factor needed for efficient proline-proline bond formation, EF-P, suppress Δrep ΔuvrD lethality. Thus replication-transcription conflicts can be alleviated by the partial sacrifice of a mechanism that reduces replicative barriers, namely translating ribosomes that reduce RNA polymerase backtracking. Suppression depends on RelA-directed synthesis of (p)ppGpp, a signalling molecule that reduces replication-transcription conflicts, with RelA activation requiring ribosomal pausing. Levels of (p)ppGpp in these suppressors also correlate inversely with the need for Rho activity, an RNA translocase that can bind to emerging transcripts and displace transcription complexes. These data illustrate the fine balance between different mechanisms in facilitating gene expression and genome duplication and demonstrate that accessory helicases are a major determinant of this balance. This balance is also critical for other aspects of bacterial survival: the mutations identified here increase persistence indicating that similar mutations could arise in naturally occurring bacterial populations facing antibiotic challenge.
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Affiliation(s)
- Kamila K. Myka
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Michelle Hawkins
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Aisha H. Syeda
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Milind K. Gupta
- School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, UK
| | - Caroline Meharg
- Institute for Global Food Security, Queen's University Belfast, David Keir Building, Malone Road, Belfast BT9 5BN, UK
| | - Mark S. Dillingham
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8, 1TD, UK
| | - Nigel J. Savery
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8, 1TD, UK
| | - Robert G. Lloyd
- Centre for Genetics and Genomics, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK
| | - Peter McGlynn
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
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95
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Gadaleta MC, Noguchi E. Regulation of DNA Replication through Natural Impediments in the Eukaryotic Genome. Genes (Basel) 2017; 8:genes8030098. [PMID: 28272375 PMCID: PMC5368702 DOI: 10.3390/genes8030098] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 03/03/2017] [Indexed: 02/07/2023] Open
Abstract
All living organisms need to duplicate their genetic information while protecting it from unwanted mutations, which can lead to genetic disorders and cancer development. Inaccuracies during DNA replication are the major cause of genomic instability, as replication forks are prone to stalling and collapse, resulting in DNA damage. The presence of exogenous DNA damaging agents as well as endogenous difficult-to-replicate DNA regions containing DNA–protein complexes, repetitive DNA, secondary DNA structures, or transcribing RNA polymerases, increases the risk of genomic instability and thus threatens cell survival. Therefore, understanding the cellular mechanisms required to preserve the genetic information during S phase is of paramount importance. In this review, we will discuss our current understanding of how cells cope with these natural impediments in order to prevent DNA damage and genomic instability during DNA replication.
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Affiliation(s)
- Mariana C Gadaleta
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
| | - Eishi Noguchi
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
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96
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Herlihy AE, de Bruin RAM. The Role of the Transcriptional Response to DNA Replication Stress. Genes (Basel) 2017; 8:E92. [PMID: 28257104 PMCID: PMC5368696 DOI: 10.3390/genes8030092] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 02/20/2017] [Accepted: 02/23/2017] [Indexed: 01/14/2023] Open
Abstract
During DNA replication many factors can result in DNA replication stress. The DNA replication stress checkpoint prevents the accumulation of replication stress-induced DNA damage and the potential ensuing genome instability. A critical role for post-translational modifications, such as phosphorylation, in the replication stress checkpoint response has been well established. However, recent work has revealed an important role for transcription in the cellular response to DNA replication stress. In this review, we will provide an overview of current knowledge of the cellular response to DNA replication stress with a specific focus on the DNA replication stress checkpoint transcriptional response and its role in the prevention of replication stress-induced DNA damage.
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Affiliation(s)
- Anna E Herlihy
- Medical Research Council Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK.
| | - Robertus A M de Bruin
- Medical Research Council Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK.
- The UCL Cancer Institute, University College London, London WC1E 6BT, UK.
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97
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S-phase checkpoint regulations that preserve replication and chromosome integrity upon dNTP depletion. Cell Mol Life Sci 2017; 74:2361-2380. [PMID: 28220209 PMCID: PMC5487892 DOI: 10.1007/s00018-017-2474-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 12/29/2016] [Accepted: 01/23/2017] [Indexed: 11/18/2022]
Abstract
DNA replication stress, an important source of genomic instability, arises upon different types of DNA replication perturbations, including those that stall replication fork progression. Inhibitors of the cellular pool of deoxynucleotide triphosphates (dNTPs) slow down DNA synthesis throughout the genome. Following depletion of dNTPs, the highly conserved replication checkpoint kinase pathway, also known as the S-phase checkpoint, preserves the functionality and structure of stalled DNA replication forks and prevents chromosome fragmentation. The underlying mechanisms involve pathways extrinsic to replication forks, such as those involving regulation of the ribonucleotide reductase activity, the temporal program of origin firing, and cell cycle transitions. In addition, the S-phase checkpoint modulates the function of replisome components to promote replication integrity. This review summarizes the various functions of the replication checkpoint in promoting replication fork stability and genome integrity in the face of replication stress caused by dNTP depletion.
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98
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Prado F, Maya D. Regulation of Replication Fork Advance and Stability by Nucleosome Assembly. Genes (Basel) 2017; 8:genes8020049. [PMID: 28125036 PMCID: PMC5333038 DOI: 10.3390/genes8020049] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/04/2017] [Accepted: 01/16/2017] [Indexed: 12/13/2022] Open
Abstract
The advance of replication forks to duplicate chromosomes in dividing cells requires the disassembly of nucleosomes ahead of the fork and the rapid assembly of parental and de novo histones at the newly synthesized strands behind the fork. Replication-coupled chromatin assembly provides a unique opportunity to regulate fork advance and stability. Through post-translational histone modifications and tightly regulated physical and genetic interactions between chromatin assembly factors and replisome components, chromatin assembly: (1) controls the rate of DNA synthesis and adjusts it to histone availability; (2) provides a mechanism to protect the integrity of the advancing fork; and (3) regulates the mechanisms of DNA damage tolerance in response to replication-blocking lesions. Uncoupling DNA synthesis from nucleosome assembly has deleterious effects on genome integrity and cell cycle progression and is linked to genetic diseases, cancer, and aging.
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Affiliation(s)
- Felix Prado
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), Spanish National Research Council (CSIC), Seville 41092, Spain.
| | - Douglas Maya
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), Spanish National Research Council (CSIC), Seville 41092, Spain.
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99
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The functions of the multi-tasking Pfh1 Pif1 helicase. Curr Genet 2017; 63:621-626. [PMID: 28054200 PMCID: PMC5504263 DOI: 10.1007/s00294-016-0675-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 12/15/2016] [Accepted: 12/19/2016] [Indexed: 11/03/2022]
Abstract
Approximately, 1% of the genes in eukaryotic genomes encode for helicases, which make the number of helicases expressed in the cell considerably high. Helicases are motor proteins that participate in many central aspects of the nuclear and mitochondrial genomes, and based on their helicase motif conservation, they are divided into different helicase families. The Pif1 family of helicases is an evolutionarily conserved helicase family that is associated with familial breast cancer in humans. The Schizosaccharomyces pombe Pfh1 helicase belongs to the Pif1 helicase family and is a multi-tasking helicase that is important for replication fork progression through natural fork barriers, for G-quadruplex unwinding, and for Okazaki fragment maturation, and these activities are potentially shared by the human Pif1 helicase. This review discusses the known functions of the Pfh1 helicase, the study of which has led to a better understanding of nucleic acid metabolism in eukaryotes.
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100
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Gambus A. Termination of Eukaryotic Replication Forks. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1042:163-187. [DOI: 10.1007/978-981-10-6955-0_8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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