1
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Fábián Z, Kakulidis ES, Hendriks IA, Kühbacher U, Larsen NB, Oliva-Santiago M, Wang J, Leng X, Dirac-Svejstrup AB, Svejstrup JQ, Nielsen ML, Caldecott K, Duxin JP. PARP1-dependent DNA-protein crosslink repair. Nat Commun 2024; 15:6641. [PMID: 39103378 DOI: 10.1038/s41467-024-50912-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 07/25/2024] [Indexed: 08/07/2024] Open
Abstract
DNA-protein crosslinks (DPCs) are toxic lesions that inhibit DNA related processes. Post-translational modifications (PTMs), including SUMOylation and ubiquitylation, play a central role in DPC resolution, but whether other PTMs are also involved remains elusive. Here, we identify a DPC repair pathway orchestrated by poly-ADP-ribosylation (PARylation). Using Xenopus egg extracts, we show that DPCs on single-stranded DNA gaps can be targeted for degradation via a replication-independent mechanism. During this process, DPCs are initially PARylated by PARP1 and subsequently ubiquitylated and degraded by the proteasome. Notably, PARP1-mediated DPC resolution is required for resolving topoisomerase 1-DNA cleavage complexes (TOP1ccs) induced by camptothecin. Using the Flp-nick system, we further reveal that in the absence of PARP1 activity, the TOP1cc-like lesion persists and induces replisome disassembly when encountered by a DNA replication fork. In summary, our work uncovers a PARP1-mediated DPC repair pathway that may underlie the synergistic toxicity between TOP1 poisons and PARP inhibitors.
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Affiliation(s)
- Zita Fábián
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Ellen S Kakulidis
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
- Biotech Research and Innovation Centre, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Ivo A Hendriks
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Ulrike Kühbacher
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Nicolai B Larsen
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Marta Oliva-Santiago
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
- Biotech Research and Innovation Centre, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Junhui Wang
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9RH, UK
| | - Xueyuan Leng
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
- Biotech Research and Innovation Centre, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - A Barbara Dirac-Svejstrup
- Department of Cellular and Molecular Medicine, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Jesper Q Svejstrup
- Department of Cellular and Molecular Medicine, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Michael L Nielsen
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark
| | - Keith Caldecott
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9RH, UK
| | - Julien P Duxin
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark.
- Biotech Research and Innovation Centre, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200, Copenhagen, Denmark.
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2
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Noireterre A, Soudet J, Bagdiul I, Stutz F. The cullin Rtt101 promotes ubiquitin-dependent DNA-protein crosslink repair across the cell cycle. Nucleic Acids Res 2024:gkae658. [PMID: 39077933 DOI: 10.1093/nar/gkae658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 06/28/2024] [Accepted: 07/16/2024] [Indexed: 07/31/2024] Open
Abstract
DNA-protein crosslinks (DPCs) challenge faithful DNA replication and smooth passage of genomic information. Our study unveils the cullin E3 ubiquitin ligase Rtt101 as a DPC repair factor. Genetic analyses demonstrate that Rtt101 is essential for resistance to a wide range of DPC types including topoisomerase 1 crosslinks, in the same pathway as the ubiquitin-dependent aspartic protease Ddi1. Using an in vivo inducible Top1-mimicking DPC system, we reveal the significant impact of Rtt101 ubiquitination on DPC removal across different cell cycle phases. High-throughput methods coupled with next-generation sequencing specifically highlight the association of Rtt101 with replisomes as well as colocalization with DPCs. Our findings establish Rtt101 as a main contributor to DPC repair throughout the yeast cell cycle.
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Affiliation(s)
- Audrey Noireterre
- Department of Molecular and Cellular Biology, University of Geneva, 1211 Geneva 4, Switzerland
| | - Julien Soudet
- Department of Molecular and Cellular Biology, University of Geneva, 1211 Geneva 4, Switzerland
| | - Ivona Bagdiul
- Department of Molecular and Cellular Biology, University of Geneva, 1211 Geneva 4, Switzerland
| | - Françoise Stutz
- Department of Molecular and Cellular Biology, University of Geneva, 1211 Geneva 4, Switzerland
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3
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Kimble MT, Sane A, Reid RJ, Johnson MJ, Rothstein R, Symington LS. Strand asymmetry in the repair of replication dependent double-strand breaks. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.17.598707. [PMID: 38948862 PMCID: PMC11212877 DOI: 10.1101/2024.06.17.598707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
Single-strand breaks (SSBs) are one of the most common endogenous lesions and have the potential to give rise to cytotoxic double-strand breaks (DSBs) during DNA replication. To investigate the mechanism of replication fork collapse at SSBs and subsequent repair, we employed Cas9 nickase (nCas9) to generate site and strand-specific nicks in the budding yeast genome. We show that nCas9-induced nicks are converted to mostly double-ended DSBs during S-phase. We find that repair of replication-dependent DSBs requires homologous recombination (HR) and is independent of canonical non-homologous end joining. Consistent with a strong bias to repair these lesions using a sister chromatid template, we observe minimal induction of inter-chromosomal HR by nCas9. Using nCas9 and a gRNA to nick either the leading or lagging strand template, we carried out a genome-wide screen to identify factors necessary for the repair of replication-dependent DSBs. All the core HR genes were recovered in the screen with both gRNAs, but we recovered components of the replication-coupled nucleosome assembly (RCNA) pathway with only the gRNA targeting the leading strand template. By use of additional gRNAs, we find that the RCNA pathway is especially important to repair a leading strand fork collapse.
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4
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Elango R, Nilavar N, Li AG, Duffey EE, Jiang Y, Nguyen D, Abakir A, Willis NA, Houseley J, Scully R. Two-ended recombination at a Flp-nickase-broken replication fork. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.10.588130. [PMID: 38645103 PMCID: PMC11030319 DOI: 10.1101/2024.04.10.588130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Collision of a replication fork with a DNA nick is thought to generate a one-ended break, fostering genomic instability. Collision of the opposing converging fork with the nick could, in principle, form a second DNA end, enabling conservative repair by homologous recombination (HR). To study mechanisms of nickase-induced HR, we developed the Flp recombinase "step arrest" nickase in mammalian cells. Flp-nickase-induced HR entails two-ended, BRCA2/RAD51-dependent short tract gene conversion (STGC), BRCA2/RAD51-independent long tract gene conversion, and discoordinated two-ended invasions. HR induced by a replication-independent break and by the Flp-nickase differ in their dependence on BRCA1 . To determine the origin of the second DNA end during Flp-nickase-induced STGC, we blocked the opposing fork using a site-specific Tus/ Ter replication fork barrier. Flp-nickase-induced STGC remained robust and two-ended. Thus, collision of a single replication fork with a Flp-nick can trigger two-ended HR, possibly reflecting replicative bypass of lagging strand nicks. This response may limit genomic instability during replication of a nicked DNA template.
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5
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Colding-Christensen CS, Kakulidis ES, Arroyo-Gomez J, Hendriks IA, Arkinson C, Fábián Z, Gambus A, Mailand N, Duxin JP, Nielsen ML. Profiling ubiquitin signalling with UBIMAX reveals DNA damage- and SCF β-Trcp1-dependent ubiquitylation of the actin-organizing protein Dbn1. Nat Commun 2023; 14:8293. [PMID: 38097601 PMCID: PMC10721886 DOI: 10.1038/s41467-023-43873-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 11/22/2023] [Indexed: 12/17/2023] Open
Abstract
Ubiquitin widely modifies proteins, thereby regulating most cellular functions. The complexity of ubiquitin signalling necessitates unbiased methods enabling global detection of dynamic protein ubiquitylation. Here, we describe UBIMAX (UBiquitin target Identification by Mass spectrometry in Xenopus egg extracts), which enriches ubiquitin-conjugated proteins and quantifies regulation of protein ubiquitylation under precise and adaptable conditions. We benchmark UBIMAX by investigating DNA double-strand break-responsive ubiquitylation events, identifying previously known targets and revealing the actin-organizing protein Dbn1 as a major target of DNA damage-induced ubiquitylation. We find that Dbn1 is targeted for proteasomal degradation by the SCFβ-Trcp1 ubiquitin ligase, in a conserved mechanism driven by ATM-mediated phosphorylation of a previously uncharacterized β-Trcp1 degron containing an SQ motif. We further show that this degron is sufficient to induce DNA damage-dependent protein degradation of a model substrate. Collectively, we demonstrate UBIMAX's ability to identify targets of stimulus-regulated ubiquitylation and reveal an SCFβ-Trcp1-mediated ubiquitylation mechanism controlled directly by the apical DNA damage response kinases.
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Affiliation(s)
- Camilla S Colding-Christensen
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Ellen S Kakulidis
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Javier Arroyo-Gomez
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Ivo A Hendriks
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Connor Arkinson
- Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, UK
- California Institute for Quantitative Biosciences and Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA, 94720, USA
| | - Zita Fábián
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Agnieszka Gambus
- Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, UK
| | - Niels Mailand
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Julien P Duxin
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark.
| | - Michael L Nielsen
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark.
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6
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Gómez-González B, Aguilera A. Break-induced RNA-DNA hybrids (BIRDHs) in homologous recombination: friend or foe? EMBO Rep 2023; 24:e57801. [PMID: 37818834 DOI: 10.15252/embr.202357801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 08/29/2023] [Accepted: 09/26/2023] [Indexed: 10/13/2023] Open
Abstract
Double-strand breaks (DSBs) are the most harmful DNA lesions, with a strong impact on cell proliferation and genome integrity. Depending on cell cycle stage, DSBs are preferentially repaired by non-homologous end joining or homologous recombination (HR). In recent years, numerous reports have revealed that DSBs enhance DNA-RNA hybrid formation around the break site. We call these hybrids "break-induced RNA-DNA hybrids" (BIRDHs) to differentiate them from sporadic R-loops consisting of DNA-RNA hybrids and a displaced single-strand DNA occurring co-transcriptionally in intact DNA. Here, we review and discuss the most relevant data about BIRDHs, with a focus on two main questions raised: (i) whether BIRDHs form by de novo transcription after a DSB or by a pre-existing nascent RNA in DNA regions undergoing transcription and (ii) whether they have a positive role in HR or are just obstacles to HR accidentally generated as an intrinsic risk of transcription. We aim to provide a comprehensive view of the exciting and yet unresolved questions about the source and impact of BIRDHs in the cell.
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Affiliation(s)
- Belén Gómez-González
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC, Seville, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC, Seville, Spain
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7
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Gasser SM, Stutz F. SUMO in the regulation of DNA repair and transcription at nuclear pores. FEBS Lett 2023; 597:2833-2850. [PMID: 37805446 DOI: 10.1002/1873-3468.14751] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2023] [Revised: 09/06/2023] [Accepted: 09/25/2023] [Indexed: 10/09/2023]
Abstract
Two related post-translational modifications, the covalent linkage of Ubiquitin and the Small Ubiquitin-related MOdifier (SUMO) to lysine residues, play key roles in the regulation of both DNA repair pathway choice and transcription. Whereas ubiquitination is generally associated with proteasome-mediated protein degradation, the impact of sumoylation has been more mysterious. In the cell nucleus, sumoylation effects are largely mediated by the relocalization of the modified targets, particularly in response to DNA damage. This is governed in part by the concentration of SUMO protease at nuclear pores [Melchior, F et al. (2003) Trends Biochem Sci 28, 612-618; Ptak, C and Wozniak, RW (2017) Adv Exp Med Biol 963, 111-126]. We review here the roles of sumoylation in determining genomic locus positioning relative to the nuclear envelope and to nuclear pores, to facilitate repair and regulate transcription.
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Affiliation(s)
- Susan M Gasser
- Department of Fundamental Microbiology, University of Lausanne, Switzerland
- ISREC Foundation, Agora Cancer Research Center, Lausanne, Switzerland
| | - Françoise Stutz
- Department of Molecular and Cellular Biology, University of Geneva, Switzerland
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8
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Marini V, Nikulenkov F, Samadder P, Juul S, Knudsen BR, Krejci L. MUS81 cleaves TOP1-derived lesions and other DNA-protein cross-links. BMC Biol 2023; 21:110. [PMID: 37194054 DOI: 10.1186/s12915-023-01614-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Accepted: 05/04/2023] [Indexed: 05/18/2023] Open
Abstract
BACKGROUND DNA-protein cross-links (DPCs) are one of the most deleterious DNA lesions, originating from various sources, including enzymatic activity. For instance, topoisomerases, which play a fundamental role in DNA metabolic processes such as replication and transcription, can be trapped and remain covalently bound to DNA in the presence of poisons or nearby DNA damage. Given the complexity of individual DPCs, numerous repair pathways have been described. The protein tyrosyl-DNA phosphodiesterase 1 (Tdp1) has been demonstrated to be responsible for removing topoisomerase 1 (Top1). Nevertheless, studies in budding yeast have indicated that alternative pathways involving Mus81, a structure-specific DNA endonuclease, could also remove Top1 and other DPCs. RESULTS This study shows that MUS81 can efficiently cleave various DNA substrates modified by fluorescein, streptavidin or proteolytically processed topoisomerase. Furthermore, the inability of MUS81 to cleave substrates bearing native TOP1 suggests that TOP1 must be either dislodged or partially degraded prior to MUS81 cleavage. We demonstrated that MUS81 could cleave a model DPC in nuclear extracts and that depletion of TDP1 in MUS81-KO cells induces sensitivity to the TOP1 poison camptothecin (CPT) and affects cell proliferation. This sensitivity is only partially suppressed by TOP1 depletion, indicating that other DPCs might require the MUS81 activity for cell proliferation. CONCLUSIONS Our data indicate that MUS81 and TDP1 play independent roles in the repair of CPT-induced lesions, thus representing new therapeutic targets for cancer cell sensitisation in combination with TOP1 inhibitors.
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Affiliation(s)
- Victoria Marini
- Department of Biology, Masaryk University, Kamenice 5/B07, Brno, 62500, Czech Republic
- International Clinical Research Center, Center for Biomolecular and Cellular Engineering, St. Anne's University Hospital Brno, Pekařská 53, Brno, 60200, Czech Republic
| | - Fedor Nikulenkov
- Department of Biology, Masaryk University, Kamenice 5/B07, Brno, 62500, Czech Republic
| | - Pounami Samadder
- Department of Biology, Masaryk University, Kamenice 5/B07, Brno, 62500, Czech Republic
| | - Sissel Juul
- Department of Molecular Biology and Genetics, Aarhus University, Universitetsbyen 81, Aarhus, 8000, Denmark
| | - Birgitta R Knudsen
- Department of Molecular Biology and Genetics, Aarhus University, Universitetsbyen 81, Aarhus, 8000, Denmark
| | - Lumir Krejci
- Department of Biology, Masaryk University, Kamenice 5/B07, Brno, 62500, Czech Republic.
- International Clinical Research Center, Center for Biomolecular and Cellular Engineering, St. Anne's University Hospital Brno, Pekařská 53, Brno, 60200, Czech Republic.
- National Centre for Biomolecular Research, Masaryk University, Kamenice 5/C04, Brno, 625 00, Czech Republic.
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9
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Noireterre A, Serbyn N, Bagdiul I, Stutz F. Ubx5-Cdc48 assists the protease Wss1 at DNA-protein crosslink sites in yeast. EMBO J 2023:e113609. [PMID: 37144685 DOI: 10.15252/embj.2023113609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 04/14/2023] [Accepted: 04/24/2023] [Indexed: 05/06/2023] Open
Abstract
DNA-protein crosslinks (DPCs) pose a serious threat to genome stability. The yeast proteases Wss1, 26S proteasome, and Ddi1 are safeguards of genome integrity by acting on a plethora of DNA-bound proteins in different cellular contexts. The AAA ATPase Cdc48/p97 is known to assist Wss1/SPRTN in clearing DNA-bound complexes; however, its contribution to DPC proteolysis remains unclear. Here, we show that the Cdc48 adaptor Ubx5 is detrimental in yeast mutants defective in DPC processing. Using an inducible site-specific crosslink, we show that Ubx5 accumulates at persistent DPC lesions in the absence of Wss1, which prevents their efficient removal from the DNA. Abolishing Cdc48 binding or complete loss of Ubx5 suppresses sensitivity of wss1∆ cells to DPC-inducing agents by favoring alternate repair pathways. We provide evidence for cooperation of Ubx5-Cdc48 and Wss1 in the genotoxin-induced degradation of RNA polymerase II (RNAPII), a described candidate substrate of Wss1. We propose that Ubx5-Cdc48 assists Wss1 for proteolysis of a subset of DNA-bound proteins. Together, our findings reveal a central role for Ubx5 in DPC clearance and repair.
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Affiliation(s)
- Audrey Noireterre
- Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland
| | - Nataliia Serbyn
- Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland
| | - Ivona Bagdiul
- Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland
| | - Françoise Stutz
- Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland
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10
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Feng YL, Liu Q, Chen RD, Liu SC, Huang ZC, Liu KM, Yang XY, Xie AY. DNA nicks induce mutational signatures associated with BRCA1 deficiency. Nat Commun 2022; 13:4285. [PMID: 35879372 PMCID: PMC9314409 DOI: 10.1038/s41467-022-32011-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 07/11/2022] [Indexed: 11/09/2022] Open
Abstract
Analysis of human cancer genome sequences has revealed specific mutational signatures associated with BRCA1-deficient tumors, but the underlying mechanisms remain poorly understood. Here, we show that one-ended DNA double strand breaks (DSBs) converted from CRISPR/Cas9-induced nicks by DNA replication, not two-ended DSBs, cause more characteristic chromosomal aberrations and micronuclei in Brca1-deficient cells than in wild-type cells. BRCA1 is required for efficient homologous recombination of these nick-converted DSBs and suppresses bias towards long tract gene conversion and tandem duplication (TD) mediated by two-round strand invasion in a replication strand asymmetry. However, aberrant repair of these nick-converted one-ended DSBs, not that of two-ended DSBs in Brca1-deficient cells, generates mutational signatures such as small indels with microhomology (MH) at the junctions, translocations and small MH-mediated TDs, resembling those in BRCA1-deficient tumors. These results suggest a major contribution of DNA nicks to mutational signatures associated with BRCA1 deficiency in cancer and the underlying mechanisms.
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Affiliation(s)
- Yi-Li Feng
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China. .,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China.
| | - Qian Liu
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China.,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China
| | - Ruo-Dan Chen
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China.,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China
| | - Si-Cheng Liu
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China.,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China
| | - Zhi-Cheng Huang
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China.,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China
| | - Kun-Ming Liu
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China.,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China
| | - Xiao-Ying Yang
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China.,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China
| | - An-Yong Xie
- Innovation Center for Minimally Invasive Technique and Device, Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310019, Hangzhou, Zhejiang, P. R. China. .,Institute of Translational Medicine, Zhejiang University School of Medicine and Zhejiang University Cancer Center, 310029, Hangzhou, Zhejiang, P. R. China.
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11
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Leng X, Duxin JP. Targeting DNA-Protein Crosslinks via Post-Translational Modifications. Front Mol Biosci 2022; 9:944775. [PMID: 35860355 PMCID: PMC9289515 DOI: 10.3389/fmolb.2022.944775] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Accepted: 06/03/2022] [Indexed: 11/13/2022] Open
Abstract
Covalent binding of proteins to DNA forms DNA-protein crosslinks (DPCs), which represent cytotoxic DNA lesions that interfere with essential processes such as DNA replication and transcription. Cells possess different enzymatic activities to counteract DPCs. These include enzymes that degrade the adducted proteins, resolve the crosslinks, or incise the DNA to remove the crosslinked proteins. An important question is how DPCs are sensed and targeted for removal via the most suited pathway. Recent advances have shown the inherent role of DNA replication in triggering DPC removal by proteolysis. However, DPCs are also efficiently sensed and removed in the absence of DNA replication. In either scenario, post-translational modifications (PTMs) on DPCs play essential and versatile roles in orchestrating the repair routes. In this review, we summarize the current knowledge of the mechanisms that trigger DPC removal via PTMs, focusing on ubiquitylation, small ubiquitin-related modifier (SUMO) conjugation (SUMOylation), and poly (ADP-ribosyl)ation (PARylation). We also briefly discuss the current knowledge gaps and emerging hypotheses in the field.
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12
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SUMO orchestrates multiple alternative DNA-protein crosslink repair pathways. Cell Rep 2021; 37:110034. [PMID: 34818558 PMCID: PMC10042627 DOI: 10.1016/j.celrep.2021.110034] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 08/27/2020] [Accepted: 11/01/2021] [Indexed: 02/05/2023] Open
Abstract
Endogenous metabolites, environmental agents, and therapeutic drugs promote formation of covalent DNA-protein crosslinks (DPCs). Persistent DPCs compromise genome integrity and are eliminated by multiple repair pathways. Aberrant Top1-DNA crosslinks, or Top1ccs, are processed by Tdp1 and Wss1 functioning in parallel pathways in Saccharomyces cerevisiae. It remains obscure how cells choose between diverse mechanisms of DPC repair. Here, we show that several SUMO biogenesis factors (Ulp1, Siz2, Slx5, and Slx8) control repair of Top1cc or an analogous DPC lesion. Genetic analysis reveals that SUMO promotes Top1cc processing in the absence of Tdp1 but has an inhibitory role if cells additionally lack Wss1. In the tdp1Δ wss1Δ mutant, the E3 SUMO ligase Siz2 stimulates sumoylation in the vicinity of the DPC, but not SUMO conjugation to Top1. This Siz2-dependent sumoylation inhibits alternative DPC repair mechanisms, including Ddi1. Our findings suggest that SUMO tunes available repair pathways to facilitate faithful DPC repair.
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13
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Gómez-González B, Ortega P, Aguilera A. Analysis of repair of replication-born double-strand breaks by sister chromatid recombination in yeast. Methods Enzymol 2021; 661:121-138. [PMID: 34776209 DOI: 10.1016/bs.mie.2021.08.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The repair of DNA double-strand breaks is crucial for cell viability and the maintenance of genome integrity. When present, the intact sister chromatid is used as the preferred repair template to restore the genetic information by homologous recombination. Although the study of the factors involved in sister chromatid recombination is hampered by the fact that both sister chromatids are indistinguishable, genetic and molecular systems based on DNA repeats have been developed to overcome this problem. In particular, the use of site-specific nucleases capable of inducing DNA nicks that replication converts into double-strand breaks has enabled the specific study of the repair of such replication-born double strand breaks by sister chromatid recombination. In this chapter, we describe detailed protocols for determining the efficiency and kinetics of this recombination reaction as well as for the genetic quantification of recombination products.
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Affiliation(s)
- Belén Gómez-González
- 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
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain.
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14
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Ortega P, Mérida-Cerro JA, Rondón AG, Gómez-González B, Aguilera A. DNA-RNA hybrids at DSBs interfere with repair by homologous recombination. eLife 2021; 10:e69881. [PMID: 34236317 PMCID: PMC8289408 DOI: 10.7554/elife.69881] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 07/07/2021] [Indexed: 12/19/2022] Open
Abstract
DNA double-strand breaks (DSBs) are the most harmful DNA lesions and their repair is crucial for cell viability and genome integrity. The readout of DSB repair may depend on whether DSBs occur at transcribed versus non-transcribed regions. Some studies have postulated that DNA-RNA hybrids form at DSBs to promote recombinational repair, but others have challenged this notion. To directly assess whether hybrids formed at DSBs promote or interfere with the recombinational repair, we have used plasmid and chromosomal-based systems for the analysis of DSB-induced recombination in Saccharomyces cerevisiae. We show that, as expected, DNA-RNA hybrid formation is stimulated at DSBs. In addition, mutations that promote DNA-RNA hybrid accumulation, such as hpr1∆ and rnh1∆ rnh201∆, cause high levels of plasmid loss when DNA breaks are induced at sites that are transcribed. Importantly, we show that high levels or unresolved DNA-RNA hybrids at the breaks interfere with their repair by homologous recombination. This interference is observed for both plasmid and chromosomal recombination and is independent of whether the DSB is generated by endonucleolytic cleavage or by DNA replication. These data support a model in which DNA-RNA hybrids form fortuitously at DNA breaks during transcription and need to be removed to allow recombinational repair, rather than playing a positive role.
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Affiliation(s)
- Pedro Ortega
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de OlavideSevilleSpain
| | - José Antonio Mérida-Cerro
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de OlavideSevilleSpain
| | - Ana G Rondón
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de OlavideSevilleSpain
| | - Belén Gómez-González
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de OlavideSevilleSpain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de OlavideSevilleSpain
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15
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Kockler ZW, Osia B, Lee R, Musmaker K, Malkova A. Repair of DNA Breaks by Break-Induced Replication. Annu Rev Biochem 2021; 90:165-191. [PMID: 33792375 DOI: 10.1146/annurev-biochem-081420-095551] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Double-strand DNA breaks (DSBs) are the most lethal type of DNA damage, making DSB repair critical for cell survival. However, some DSB repair pathways are mutagenic and promote genome rearrangements, leading to genome destabilization. One such pathway is break-induced replication (BIR), which repairs primarily one-ended DSBs, similar to those formed by collapsed replication forks or telomere erosion. BIR is initiated by the invasion of a broken DNA end into a homologous template, synthesizes new DNA within the context of a migrating bubble, and is associated with conservative inheritance of new genetic material. This mode of synthesis is responsible for a high level of genetic instability associated with BIR. Eukaryotic BIR was initially investigated in yeast, but now it is also actively studied in mammalian systems. Additionally, a significant breakthrough has been made regarding the role of microhomology-mediated BIR in the formation of complex genomic rearrangements that underly various human pathologies.
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Affiliation(s)
- Z W Kockler
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - B Osia
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - R Lee
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - K Musmaker
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - A Malkova
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
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16
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Vrtis KB, Dewar JM, Chistol G, Wu RA, Graham TGW, Walter JC. Single-strand DNA breaks cause replisome disassembly. Mol Cell 2021; 81:1309-1318.e6. [PMID: 33484638 DOI: 10.1016/j.molcel.2020.12.039] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2020] [Revised: 12/11/2020] [Accepted: 12/23/2020] [Indexed: 11/16/2022]
Abstract
DNA damage impedes replication fork progression and threatens genome stability. Upon encounter with most DNA adducts, the replicative CMG helicase (CDC45-MCM2-7-GINS) stalls or uncouples from the point of synthesis, yet eventually resumes replication. However, little is known about the effect on replication of single-strand breaks or "nicks," which are abundant in mammalian cells. Using Xenopus egg extracts, we reveal that CMG collision with a nick in the leading strand template generates a blunt-ended double-strand break (DSB). Moreover, CMG, which encircles the leading strand template, "runs off" the end of the DSB. In contrast, CMG collision with a lagging strand nick generates a broken end with a single-stranded overhang. In this setting, CMG translocates along double-stranded DNA beyond the break and is then ubiquitylated and removed from chromatin by the same pathway used during replication termination. Our results show that nicks are uniquely dangerous DNA lesions that invariably cause replisome disassembly, and they suggest that CMG cannot be stored on dsDNA while cells resolve replication stress.
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Affiliation(s)
- Kyle B Vrtis
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - James M Dewar
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - Gheorghe Chistol
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - R Alex Wu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - Thomas G W Graham
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - Johannes C Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston, MA 02115, USA.
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17
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Kühbacher U, Duxin JP. How to fix DNA-protein crosslinks. DNA Repair (Amst) 2020; 94:102924. [PMID: 32683310 PMCID: PMC7511601 DOI: 10.1016/j.dnarep.2020.102924] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 07/03/2020] [Accepted: 07/05/2020] [Indexed: 12/18/2022]
Abstract
Proteins that act on DNA, or are in close proximity to it, can become inadvertently crosslinked to DNA and form highly toxic lesions, known as DNA-protein crosslinks (DPCs). DPCs are generated by different chemotherapeutics, environmental or endogenous sources of crosslinking agents, or by lesions on DNA that stall the catalytic cycle of certain DNA processing enzymes. These bulky adducts impair processes on DNA such as DNA replication or transcription, and therefore pose a serious threat to genome integrity. The large diversity of DPCs suggests that there is more than one canonical mechanism to repair them. Indeed, many different enzymes have been shown to act on DPCs by either processing the protein, the DNA or the crosslink itself. In addition, the cell cycle stage or cell type are likely to dictate pathway choice. In recent years, a detailed understanding of DPC repair during S phase has started to emerge. Here, we review the current knowledge on the mechanisms of replication-coupled DPC repair, and describe and also speculate on possible pathways that remove DPCs outside of S phase. Moreover, we highlight a recent paradigm shifting finding that indicates that DPCs are not always detrimental, but can also play a protective role, preserving the genome from more deleterious forms of DNA damage.
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Affiliation(s)
- Ulrike Kühbacher
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Julien P Duxin
- The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark.
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18
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Pardo B, Moriel‐Carretero M, Vicat T, Aguilera A, Pasero P. Homologous recombination and Mus81 promote replication completion in response to replication fork blockage. EMBO Rep 2020; 21:e49367. [PMID: 32419301 PMCID: PMC7332989 DOI: 10.15252/embr.201949367] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Revised: 04/16/2020] [Accepted: 04/20/2020] [Indexed: 12/19/2022] Open
Abstract
Impediments to DNA replication threaten genome stability. The homologous recombination (HR) pathway has been involved in the restart of blocked replication forks. Here, we used a method to increase yeast cell permeability in order to study at the molecular level the fate of replication forks blocked by DNA topoisomerase I poisoning by camptothecin (CPT). Our results indicate that Rad52 and Rad51 HR factors are required to complete DNA replication in response to CPT. Recombination events occurring during S phase do not generally lead to the restart of DNA synthesis but rather protect blocked forks until they merge with convergent forks. This fusion generates structures requiring their resolution by the Mus81 endonuclease in G2 /M. At the global genome level, the multiplicity of replication origins in eukaryotic genomes and the fork protection mechanism provided by HR appear therefore to be essential to complete DNA replication in response to fork blockage.
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Affiliation(s)
- Benjamin Pardo
- Institut de Génétique HumaineUniversité de Montpellier‐CNRSMontpellierFrance
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMERUniversidad de Sevilla‐CSIC‐Universidad Pablo de OlavideSevilleSpain
| | - María Moriel‐Carretero
- Institut de Génétique HumaineUniversité de Montpellier‐CNRSMontpellierFrance
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMERUniversidad de Sevilla‐CSIC‐Universidad Pablo de OlavideSevilleSpain
- Present address:
Centre de Recherche en Biologie cellulaire de MontpellierUniversité de Montpellier‐CNRSMontpellierFrance
| | - Thibaud Vicat
- Institut de Génétique HumaineUniversité de Montpellier‐CNRSMontpellierFrance
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMERUniversidad de Sevilla‐CSIC‐Universidad Pablo de OlavideSevilleSpain
| | - Philippe Pasero
- Institut de Génétique HumaineUniversité de Montpellier‐CNRSMontpellierFrance
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19
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Bittmann J, Grigaitis R, Galanti L, Amarell S, Wilfling F, Matos J, Pfander B. An advanced cell cycle tag toolbox reveals principles underlying temporal control of structure-selective nucleases. eLife 2020; 9:e52459. [PMID: 32352375 PMCID: PMC7220381 DOI: 10.7554/elife.52459] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Accepted: 04/29/2020] [Indexed: 12/26/2022] Open
Abstract
Cell cycle tags allow to restrict target protein expression to specific cell cycle phases. Here, we present an advanced toolbox of cell cycle tag constructs in budding yeast with defined and compatible peak expression that allow comparison of protein functionality at different cell cycle phases. We apply this technology to the question of how and when Mus81-Mms4 and Yen1 nucleases act on DNA replication or recombination structures. Restriction of Mus81-Mms4 to M phase but not S phase allows a wildtype response to various forms of replication perturbation and DNA damage in S phase, suggesting it acts as a post-replicative resolvase. Moreover, we use cell cycle tags to reinstall cell cycle control to a deregulated version of Yen1, showing that its premature activation interferes with the response to perturbed replication. Curbing resolvase activity and establishing a hierarchy of resolution mechanisms are therefore the principal reasons underlying resolvase cell cycle regulation.
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Affiliation(s)
- Julia Bittmann
- Max Planck Institute of Biochemistry, DNA Replication and Genome IntegrityMartinsriedGermany
| | - Rokas Grigaitis
- Institute of Biochemistry, Eidgenössische Technische Hochschule, ZürichZürichSwitzerland
| | - Lorenzo Galanti
- Max Planck Institute of Biochemistry, DNA Replication and Genome IntegrityMartinsriedGermany
| | - Silas Amarell
- Max Planck Institute of Biochemistry, DNA Replication and Genome IntegrityMartinsriedGermany
| | - Florian Wilfling
- Max Planck Institute of Biochemistry, Molecular Cell BiologyMartinsriedGermany
| | - Joao Matos
- Institute of Biochemistry, Eidgenössische Technische Hochschule, ZürichZürichSwitzerland
| | - Boris Pfander
- Max Planck Institute of Biochemistry, DNA Replication and Genome IntegrityMartinsriedGermany
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20
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Study of Polyphenol Content and Antioxidant Properties of Various Mix of Chocolate Milk Masses with Different Protein Content. Antioxidants (Basel) 2020; 9:antiox9040299. [PMID: 32260255 PMCID: PMC7222213 DOI: 10.3390/antiox9040299] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 04/01/2020] [Accepted: 04/01/2020] [Indexed: 12/15/2022] Open
Abstract
The aim of the study was to analyze the antioxidant character of conched chocolate milk masses, taking into account different protein content in milk. For the study, cocoa liquor obtained from roasted and unroasted cocoa beans from different regions, as well as milk powder obtained by spray and cylindrical drying were used. The analysis that was carried out showed that the protein content of powdered milk products ranged from about 11.6% (w/w) to over 31% (w/w). Lower content of polyphenols and lower antioxidant activity were shown in the masses to which the addition of milk with higher protein content was applied. The analysis of antioxidant character of chocolate milk masses showed higher total polyphenols content in masses prepared from unroasted cocoa beans liquor.
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21
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Jakobsen KP, Nielsen KO, Løvschal KV, Rødgaard M, Andersen AH, Bjergbæk L. Minimal Resection Takes Place during Break-Induced Replication Repair of Collapsed Replication Forks and Is Controlled by Strand Invasion. Cell Rep 2020; 26:836-844.e3. [PMID: 30673606 DOI: 10.1016/j.celrep.2018.12.108] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 12/04/2018] [Accepted: 12/26/2018] [Indexed: 11/16/2022] Open
Abstract
A natural and frequently occurring replication problem is generated by the action of topoisomerase I (Top1). Trapping of Top1 in a cleavage complex on the DNA generates a protein-linked DNA nick (PDN), which upon DNA replication can be transformed into a one-ended double-strand break (DSB). Break-induced replication (BIR) has been recognized as a critical repair mechanism of one-ended DSBs. Here, we have investigated resection at a one-ended DSB formed exclusively during replication due to Top1-mimicking damage. We show that resection is minimal, and only when strand invasion is abolished is extensive resection detected. When DNA synthesis is slowed by hydroxyurea treatment, extended resection is not observed, which suggests that strand invasion and/or heteroduplex formation restrains resection. Our results demonstrate that the BIR pathway acting during S phase is tailored to prevent hazardous effects of naturally and frequently occurring DNA breaks such as Top1-generated PDNs.
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Affiliation(s)
- Kristoffer P Jakobsen
- Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Building 1130, 8000 Aarhus C, Denmark
| | - Kirstine O Nielsen
- Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Building 1130, 8000 Aarhus C, Denmark
| | - Katrine V Løvschal
- Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Building 1130, 8000 Aarhus C, Denmark
| | - Morten Rødgaard
- Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Building 1130, 8000 Aarhus C, Denmark
| | - Anni H Andersen
- Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Building 1130, 8000 Aarhus C, Denmark
| | - Lotte Bjergbæk
- Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, Building 1130, 8000 Aarhus C, Denmark.
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22
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The Aspartic Protease Ddi1 Contributes to DNA-Protein Crosslink Repair in Yeast. Mol Cell 2020; 77:1066-1079.e9. [PMID: 31902667 DOI: 10.1016/j.molcel.2019.12.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 10/24/2019] [Accepted: 12/09/2019] [Indexed: 01/07/2023]
Abstract
Naturally occurring or drug-induced DNA-protein crosslinks (DPCs) interfere with key DNA transactions if not repaired in a timely manner. The unique family of DPC-specific proteases Wss1/SPRTN targets DPC protein moieties for degradation, including stabilized topoisomerase-1 cleavage complexes (Top1ccs). Here, we describe that the efficient DPC disassembly requires Ddi1, another conserved predicted protease in Saccharomyces cerevisiae. We found Ddi1 in a genetic screen of the tdp1 wss1 mutant defective in Top1cc processing. Ddi1 is recruited to a persistent Top1cc-like DPC lesion in an S phase-dependent manner to assist in the eviction of crosslinked protein from DNA. Loss of Ddi1 or its putative protease activity hypersensitizes cells to DPC trapping agents independently from Wss1 and 26S proteasome, implying its broader role in DPC repair. Among the potential Ddi1 targets, we found the core component of Pol II and show that its genotoxin-induced degradation is impaired in ddi1. We propose that the Ddi1 protease contributes to DPC proteolysis.
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23
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Ortega P, Gómez-González B, Aguilera A. Rpd3L and Hda1 histone deacetylases facilitate repair of broken forks by promoting sister chromatid cohesion. Nat Commun 2019; 10:5178. [PMID: 31729385 PMCID: PMC6858524 DOI: 10.1038/s41467-019-13210-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 10/22/2019] [Indexed: 12/13/2022] Open
Abstract
Genome stability involves accurate replication and DNA repair. Broken replication forks, such as those encountering a nick, lead to double strand breaks (DSBs), which are preferentially repaired by sister-chromatid recombination (SCR). To decipher the role of chromatin in eukaryotic DSB repair, here we analyze a collection of yeast chromatin-modifying mutants using a previously developed system for the molecular analysis of repair of replication-born DSBs by SCR based on a mini-HO site. We confirm the candidates through FLP-based systems based on a mutated version of the FLP flipase that causes nicks on either the leading or lagging DNA strands. We demonstrate that Rpd3L and Hda1 histone deacetylase (HDAC) complexes contribute to the repair of replication-born DSBs by facilitating cohesin loading, with no effect on other types of homology-dependent repair, thus preventing genome instability. We conclude that histone deacetylation favors general sister chromatid cohesion as a necessary step in SCR.
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Affiliation(s)
- Pedro Ortega
- 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.
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain.
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24
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Wong RP, García-Rodríguez N, Zilio N, Hanulová M, Ulrich HD. Processing of DNA Polymerase-Blocking Lesions during Genome Replication Is Spatially and Temporally Segregated from Replication Forks. Mol Cell 2019; 77:3-16.e4. [PMID: 31607544 DOI: 10.1016/j.molcel.2019.09.015] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 08/23/2019] [Accepted: 09/10/2019] [Indexed: 11/25/2022]
Abstract
Tracing DNA repair factors by fluorescence microscopy provides valuable information about how DNA damage processing is orchestrated within cells. Most repair pathways involve single-stranded DNA (ssDNA), making replication protein A (RPA) a hallmark of DNA damage and replication stress. RPA foci emerging during S phase in response to tolerable loads of polymerase-blocking lesions are generally thought to indicate stalled replication intermediates. We now report that in budding yeast they predominantly form far away from sites of ongoing replication, and they do not overlap with any of the repair centers associated with collapsed replication forks or double-strand breaks. Instead, they represent sites of postreplicative DNA damage bypass involving translesion synthesis and homologous recombination. We propose that most RPA and recombination foci induced by polymerase-blocking lesions in the replication template are clusters of repair tracts arising from replication centers by polymerase re-priming and subsequent expansion of daughter-strand gaps over the course of S phase.
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Affiliation(s)
- Ronald P Wong
- Institute of Molecular Biology, 55128 Mainz, Germany
| | | | - Nicola Zilio
- Institute of Molecular Biology, 55128 Mainz, Germany
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25
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Ma CH, Su BY, Maciaszek A, Fan HF, Guga P, Jayaram M. A Flp-SUMO hybrid recombinase reveals multi-layered copy number control of a selfish DNA element through post-translational modification. PLoS Genet 2019; 15:e1008193. [PMID: 31242181 PMCID: PMC6594588 DOI: 10.1371/journal.pgen.1008193] [Citation(s) in RCA: 6] [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: 02/11/2019] [Accepted: 05/13/2019] [Indexed: 12/30/2022] Open
Abstract
Mechanisms for highly efficient chromosome-associated equal segregation, and for maintenance of steady state copy number, are at the heart of the evolutionary success of the 2-micron plasmid as a stable multi-copy extra-chromosomal selfish DNA element present in the yeast nucleus. The Flp site-specific recombination system housed by the plasmid, which is central to plasmid copy number maintenance, is regulated at multiple levels. Transcription of the FLP gene is fine-tuned by the repressor function of the plasmid-coded partitioning proteins Rep1 and Rep2 and their antagonist Raf1, which is also plasmid-coded. In addition, the Flp protein is regulated by the host's post-translational modification machinery. Utilizing a Flp-SUMO fusion protein, which functionally mimics naturally sumoylated Flp, we demonstrate that the modification signals ubiquitination of Flp, followed by its proteasome-mediated degradation. Furthermore, reduced binding affinity and cooperativity of the modified Flp decrease its association with the plasmid FRT (Flp recombination target) sites, and/or increase its dissociation from them. The resulting attenuation of strand cleavage and recombination events safeguards against runaway increase in plasmid copy number, which is deleterious to the host-and indirectly-to the plasmid. These results have broader relevance to potential mechanisms by which selfish genomes minimize fitness conflicts with host genomes by holding in check the extra genetic load they pose.
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Affiliation(s)
- Chien-Hui Ma
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States of America
| | - Bo-Yu Su
- Department of Life Sciences and Institute of Genome Sciences, Biophotonics and Molecular Imaging Research Center, National Yang-Ming University, Taipei City, Taiwan
| | - Anna Maciaszek
- Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Department of Bioorganic Chemistry, Lodz, Poland
| | - Hsiu-Fang Fan
- Department of Life Sciences and Institute of Genome Sciences, Biophotonics and Molecular Imaging Research Center, National Yang-Ming University, Taipei City, Taiwan
| | - Piotr Guga
- Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Department of Bioorganic Chemistry, Lodz, Poland
| | - Makkuni Jayaram
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States of America
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26
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Jakobsen KP, Andersen AH, Bjergbæk L. Abortive activity of Topoisomerase I: a challenge for genome integrity? Curr Genet 2019; 65:1141-1144. [DOI: 10.1007/s00294-019-00984-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 04/24/2019] [Accepted: 04/25/2019] [Indexed: 01/19/2023]
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27
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Song X, Beck CR, Du R, Campbell IM, Coban-Akdemir Z, Gu S, Breman AM, Stankiewicz P, Ira G, Shaw CA, Lupski JR. Predicting human genes susceptible to genomic instability associated with Alu/ Alu-mediated rearrangements. Genome Res 2018; 28:1228-1242. [PMID: 29907612 PMCID: PMC6071635 DOI: 10.1101/gr.229401.117] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 06/06/2018] [Indexed: 12/14/2022]
Abstract
Alu elements, the short interspersed element numbering more than 1 million copies per human genome, can mediate the formation of copy number variants (CNVs) between substrate pairs. These Alu/Alu-mediated rearrangements (AAMRs) can result in pathogenic variants that cause diseases. To investigate the impact of AAMR on gene variation and human health, we first characterized Alus that are involved in mediating CNVs (CNV-Alus) and observed that these Alus tend to be evolutionarily younger. We then computationally generated, with the assistance of a supercomputer, a test data set consisting of 78 million Alu pairs and predicted ∼18% of them are potentially susceptible to AAMR. We further determined the relative risk of AAMR in 12,074 OMIM genes using the count of predicted CNV-Alu pairs and experimentally validated the predictions with 89 samples selected by correlating predicted hotspots with a database of CNVs identified by clinical chromosomal microarrays (CMAs) on the genomes of approximately 54,000 subjects. We fine-mapped 47 duplications, 40 deletions, and two complex rearrangements and examined a total of 52 breakpoint junctions of simple CNVs. Overall, 94% of the candidate breakpoints were at least partially Alu mediated. We successfully predicted all (100%) of Alu pairs that mediated deletions (n = 21) and achieved an 87% positive predictive value overall when including AAMR-generated deletions and duplications. We provided a tool, AluAluCNVpredictor, for assessing AAMR hotspots and their role in human disease. These results demonstrate the utility of our predictive model and provide insights into the genomic features and molecular mechanisms underlying AAMR.
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Affiliation(s)
- Xiaofei Song
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Christine R Beck
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Renqian Du
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Ian M Campbell
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Zeynep Coban-Akdemir
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Shen Gu
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Amy M Breman
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Baylor Genetics, Houston, Texas 77021, USA
| | - Pawel Stankiewicz
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Baylor Genetics, Houston, Texas 77021, USA
| | - Grzegorz Ira
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Chad A Shaw
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Baylor Genetics, Houston, Texas 77021, USA
| | - James R Lupski
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
- Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
- Texas Children's Hospital, Houston, Texas 77030, USA
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28
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Abstract
A natural and frequent occurring replication insult is generated by the action of DNA Topoisomerase I (Top1). When Top1 gets trapped in a cleavage complex on the DNA, a protein-linked DNA nick (PDN) is generated. Today it is known that PDNs are generated at a high incidence in the cell. If not rapidly removed, PDNs can have a profound impact on cell destiny, as a nick in proliferating cells is passively transformed into a single-ended DSB, when encountered by the replication machinery. A DSB can in turn lead to chromosomal rearrangements and thus jeopardize genome stability if not appropriately repaired. In order to study repair pathways associated with PDNs, we have developed a cellular system (Flp-nick), where we can generate a single PDN at a specific genomic site in the model organism Saccharomyces cerevisiae. The system takes advantages of the Flp recombinase, which catalytically operates like Top1 by generating a nick in the DNA backbone and during this process becomes covalently linked to the DNA. Flp cleaves at well-defined target sites. Thus, a target site has been inserted in the genome and a mutant Flp, which cleaves but do not religate, is expressed. In this way, a single PDN mimicking the one generated by Top1 is induced at a known genomic site. The Flp-nick system allows detailed molecular analysis of repair pathways associated with this type of damage and can be designed to study repair at any genomic context.
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29
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Sakofsky CJ, Malkova A. Break induced replication in eukaryotes: mechanisms, functions, and consequences. Crit Rev Biochem Mol Biol 2017; 52:395-413. [PMID: 28427283 DOI: 10.1080/10409238.2017.1314444] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Break-induced replication (BIR) is an important pathway specializing in repair of one-ended double-strand DNA breaks (DSBs). This type of DSB break typically arises at collapsed replication forks or at eroded telomeres. BIR initiates by invasion of a broken DNA end into a homologous template followed by initiation of DNA synthesis that can proceed for hundreds of kilobases. This synthesis is drastically different from S-phase replication in that instead of a replication fork, BIR proceeds via a migrating bubble and is associated with conservative inheritance of newly synthesized DNA. This unusual mode of DNA replication is responsible for frequent genetic instabilities associated with BIR, including hyper-mutagenesis, which can lead to the formation of mutation clusters, extensive loss of heterozygosity, chromosomal translocations, copy-number variations and complex genomic rearrangements. In addition to budding yeast experimental systems that were initially employed to investigate eukaryotic BIR, recent studies in different organisms including humans, have provided multiple examples of BIR initiated within different cellular contexts, including collapsed replication fork and telomere maintenance in the absence of telomerase. In addition, significant progress has been made towards understanding microhomology-mediated BIR (MMBIR) that can promote complex chromosomal rearrangements, including those associated with cancer and those leading to a number of neurological disorders in humans.
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Affiliation(s)
- Cynthia J Sakofsky
- a Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences , US National Institutes of Health , Research Triangle Park , NC , USA
| | - Anna Malkova
- b Department of Biology , University of Iowa , Iowa City , IA , USA
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30
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Abstract
The fields of molecular genetics, biotechnology and synthetic biology are demanding ever more sophisticated molecular tools for programmed precise modification of cell genomic DNA and other DNA sequences. This review presents the current state of knowledge and development of one important group of DNA-modifying enzymes, the site-specific recombinases (SSRs). SSRs are Nature's 'molecular machines' for cut-and-paste editing of DNA molecules by inserting, deleting or inverting precisely defined DNA segments. We survey the SSRs that have been put to use, and the types of applications for which they are suitable. We also discuss problems associated with uses of SSRs, how these problems can be minimized, and how recombinases are being re-engineered for improved performance and novel applications.
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31
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Rtt107 BRCT domains act as a targeting module in the DNA damage response. DNA Repair (Amst) 2015; 37:22-32. [PMID: 26641499 DOI: 10.1016/j.dnarep.2015.10.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Revised: 10/22/2015] [Accepted: 10/22/2015] [Indexed: 01/11/2023]
Abstract
Cells are constantly exposed to assaults that cause DNA damage, which must be detected and repaired to prevent genome instability. The DNA damage response is mediated by key kinases that activate various signaling pathways. In Saccharomyces cerevisiae, one of these kinases is Mec1, which phosphorylates numerous targets, including H2A and the DNA damage protein Rtt107. In addition to being phosphorylated, Rtt107 contains six BRCA1 C-terminal (BRCT) domains, which typically recognize phospho-peptides. Thus Rtt107 represented an opportunity to study complementary aspects of the phosphorylation cascades within one protein. Here we sought to describe the functional roles of the multiple BRCT domains in Rtt107. Rtt107 BRCT5/6 facilitated recruitment to sites of DNA lesions via its interaction with phosphorylated H2A. Rtt107 BRCT3/4 also contributed to Rtt107 recruitment, but BRCT3/4 was not sufficient for recruitment when BRCT5/6 was absent. Intriguingly, both mutations that affected Rtt107 recruitment also abrogated its phosphorylation. Pointing to its modular nature, replacing Rtt107 BRCT5/6 with the BRCT domains from the checkpoint protein Rad9 was able to sustain Rtt107 function. Although Rtt107 physically interacts with both the endonuclease Slx4 and the DNA replication and repair protein Dpb11, only Slx4 was dependent on Rtt107 for its recruitment to DNA lesions. Fusing Rtt107 BRCT5/6 to Slx4, which presumably allows artificial recruitment of Slx4 to DNA lesions, alleviated some phenotypes of rtt107Δ mutants, indicating the functional importance of Slx4 recruitment. Together this data revealed a key function of the Rtt107 BRCT domains for targeting of both itself and its interaction partners to DNA lesions.
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32
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Mayle R, Campbell IM, Beck CR, Yu Y, Wilson M, Shaw CA, Bjergbaek L, Lupski JR, Ira G. DNA REPAIR. Mus81 and converging forks limit the mutagenicity of replication fork breakage. Science 2015; 349:742-7. [PMID: 26273056 DOI: 10.1126/science.aaa8391] [Citation(s) in RCA: 142] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Most spontaneous DNA double-strand breaks (DSBs) result from replication-fork breakage. Break-induced replication (BIR), a genome rearrangement-prone repair mechanism that requires the Pol32/POLD3 subunit of eukaryotic DNA Polδ, was proposed to repair broken forks, but how genome destabilization is avoided was unknown. We show that broken fork repair initially uses error-prone Pol32-dependent synthesis, but that mutagenic synthesis is limited to within a few kilobases from the break by Mus81 endonuclease and a converging fork. Mus81 suppresses template switches between both homologous sequences and diverged human Alu repetitive elements, highlighting its importance for stability of highly repetitive genomes. We propose that lack of a timely converging fork or Mus81 may propel genome instability observed in cancer.
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Affiliation(s)
- Ryan Mayle
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Ian M Campbell
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Christine R Beck
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Yang Yu
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Marenda Wilson
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Chad A Shaw
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Lotte Bjergbaek
- Department of Molecular Biology and Genetics, University of Aarhus, Aarhus 8000, Denmark
| | - James R Lupski
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. Department of Pediatrics, and Human Genome Sequencing Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. Texas Children's Hospital, Houston, TX 77030, USA
| | - Grzegorz Ira
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
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33
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Abstract
Homology-dependent exchange of genetic information between DNA molecules has a profound impact on the maintenance of genome integrity by facilitating error-free DNA repair, replication, and chromosome segregation during cell division as well as programmed cell developmental events. This chapter will focus on homologous mitotic recombination in budding yeast Saccharomyces cerevisiae. However, there is an important link between mitotic and meiotic recombination (covered in the forthcoming chapter by Hunter et al. 2015) and many of the functions are evolutionarily conserved. Here we will discuss several models that have been proposed to explain the mechanism of mitotic recombination, the genes and proteins involved in various pathways, the genetic and physical assays used to discover and study these genes, and the roles of many of these proteins inside the cell.
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34
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Kristoffersen EL, Jørgensen LA, Franch O, Etzerodt M, Frøhlich R, Bjergbæk L, Stougaard M, Ho YP, Knudsen BR. Real-time investigation of human topoisomerase I reaction kinetics using an optical sensor: a fast method for drug screening and determination of active enzyme concentrations. NANOSCALE 2015; 7:9825-9834. [PMID: 25963854 DOI: 10.1039/c5nr01474c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment.
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35
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Abstract
Genetic instabilities, including mutations and chromosomal rearrangements, lead to cancer and other diseases in humans and play an important role in evolution. A frequent cause of genetic instabilities is double-strand DNA breaks (DSBs), which may arise from a wide range of exogeneous and endogeneous cellular factors. Although the repair of DSBs is required, some repair pathways are dangerous because they may destabilize the genome. One such pathway, break-induced replication (BIR), is the mechanism for repairing DSBs that possesses only one repairable end. This situation commonly arises as a result of eroded telomeres or collapsed replication forks. Although BIR plays a positive role in repairing DSBs, it can alternatively be a dangerous source of several types of genetic instabilities, including loss of heterozygosity, telomere maintenance in the absence of telomerase, and non-reciprocal translocations. Also, mutation rates in BIR are about 1000 times higher as compared to normal DNA replication. In addition, micro-homology-mediated BIR (MMBIR), which is a mechanism related to BIR, can generate copy-number variations (CNVs) as well as various complex chromosomal rearrangements. Overall, activation of BIR may contribute to genomic destabilization resulting in substantial biological consequences including those affecting human health.
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Affiliation(s)
| | | | - Anna Malkova
- Author to whom correspondence should be addressed; ; Tel.: +1-317-278-5717; Fax: +1-317-274-2946
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36
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Larsen NB, Sass E, Suski C, Mankouri HW, Hickson ID. The Escherichia coli Tus-Ter replication fork barrier causes site-specific DNA replication perturbation in yeast. Nat Commun 2014; 5:3574. [PMID: 24705096 DOI: 10.1038/ncomms4574] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 03/06/2014] [Indexed: 01/01/2023] Open
Abstract
Replication fork (RF) pausing occurs at both 'programmed' sites and non-physiological barriers (for example, DNA adducts). Programmed RF pausing is required for site-specific DNA replication termination in Escherichia coli, and this process requires the binding of the polar terminator protein, Tus, to specific DNA sequences called Ter. Here, we demonstrate that Tus-Ter modules also induce polar RF pausing when engineered into the Saccharomyces cerevisiae genome. This heterologous RF barrier is distinct from a number of previously characterized, protein-mediated, RF pause sites in yeast, as it is neither Tof1-dependent nor counteracted by the Rrm3 helicase. Although the yeast replisome can overcome RF pausing at Tus-Ter modules, this event triggers site-specific homologous recombination that requires the RecQ helicase, Sgs1, for its timely resolution. We propose that Tus-Ter can be utilized as a versatile, site-specific, heterologous DNA replication-perturbing system, with a variety of potential applications.
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Affiliation(s)
- Nicolai B Larsen
- Nordea Center for Healthy Aging, Department of Cellular and Molecular Medicine, Panum Institute 18.1, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark
| | - Ehud Sass
- 1] Nordea Center for Healthy Aging, Department of Cellular and Molecular Medicine, Panum Institute 18.1, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark [2] Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK [3]
| | - Catherine Suski
- 1] Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK [2]
| | - Hocine W Mankouri
- 1] Nordea Center for Healthy Aging, Department of Cellular and Molecular Medicine, Panum Institute 18.1, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark [2] Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
| | - Ian D Hickson
- 1] Nordea Center for Healthy Aging, Department of Cellular and Molecular Medicine, Panum Institute 18.1, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark [2] Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
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37
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Abstract
Recombination-dependent DNA replication, often called break-induced replication (BIR), was initially invoked to explain recombination events in bacteriophage but it has recently been recognized as a fundamentally important mechanism to repair double-strand chromosome breaks in eukaryotes. This mechanism appears to be critically important in the restarting of stalled and broken replication forks and in maintaining the integrity of eroded telomeres. Although BIR helps preserve genome integrity during replication, it also promotes genome instability by the production of loss of heterozygosity and the formation of nonreciprocal translocations, as well as in the generation of complex chromosomal rearrangements.
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Affiliation(s)
- Ranjith P Anand
- Rosenstiel Basic Medical Sciences Research Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02254-9110
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38
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Dion V, Kalck V, Seeber A, Schleker T, Gasser SM. Cohesin and the nucleolus constrain the mobility of spontaneous repair foci. EMBO Rep 2013; 14:984-91. [PMID: 24018421 PMCID: PMC3818071 DOI: 10.1038/embor.2013.142] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Revised: 08/13/2013] [Accepted: 08/13/2013] [Indexed: 12/24/2022] Open
Abstract
The regulation of chromatin mobility in response to DNA damage is important for homologous recombination in yeast. Anchorage reduces rates of recombination, whereas increased chromatin mobility correlates with more efficient homology search. Here we tracked the mobility and localization of spontaneous S-phase lesions bound by Rad52, and find that these foci have reduced movement, unlike enzymatically induced double-strand breaks. Moreover, spontaneous repair foci are positioned in the nuclear core, abutting the nucleolus. We show that cohesin and nucleolar integrity constrain the mobility of these foci, consistent with the notion that spontaneous, S-phase damage is preferentially repaired from the sister chromatid.
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Affiliation(s)
- Vincent Dion
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel, Switzerland
| | - Véronique Kalck
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel, Switzerland
| | - Andrew Seeber
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel, Switzerland
- Faculty of Natural Sciences, University of Basel, CH-4056 Basel, Switzerland
| | - Thomas Schleker
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel, Switzerland
| | - Susan M Gasser
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel, Switzerland
- Faculty of Natural Sciences, University of Basel, CH-4056 Basel, Switzerland
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39
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Replication checkpoint: tuning and coordination of replication forks in s phase. Genes (Basel) 2013; 4:388-434. [PMID: 24705211 PMCID: PMC3924824 DOI: 10.3390/genes4030388] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 07/30/2013] [Accepted: 08/02/2013] [Indexed: 12/01/2022] Open
Abstract
Checkpoints monitor critical cell cycle events such as chromosome duplication and segregation. They are highly conserved mechanisms that prevent progression into the next phase of the cell cycle when cells are unable to accomplish the previous event properly. During S phase, cells also provide a surveillance mechanism called the DNA replication checkpoint, which consists of a conserved kinase cascade that is provoked by insults that block or slow down replication forks. The DNA replication checkpoint is crucial for maintaining genome stability, because replication forks become vulnerable to collapse when they encounter obstacles such as nucleotide adducts, nicks, RNA-DNA hybrids, or stable protein-DNA complexes. These can be exogenously induced or can arise from endogenous cellular activity. Here, we summarize the initiation and transduction of the replication checkpoint as well as its targets, which coordinate cell cycle events and DNA replication fork stability.
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40
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Dion V, Gasser SM. Chromatin movement in the maintenance of genome stability. Cell 2013; 152:1355-64. [PMID: 23498942 DOI: 10.1016/j.cell.2013.02.010] [Citation(s) in RCA: 166] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Indexed: 11/24/2022]
Abstract
Mechanistic analyses based on improved imaging techniques have begun to explore the biological implications of chromatin movement within the nucleus. Studies in both prokaryotes and eukaryotes have shed light on what regulates the mobility of DNA over long distances. Interestingly, in eukaryotes, genomic loci increase their movement in response to double-strand break induction. Break mobility, in turn, correlates with the efficiency of repair by homologous recombination. We review here the source and regulation of DNA mobility and discuss how it can both contribute to and jeopardize genome stability.
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Affiliation(s)
- Vincent Dion
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
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41
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Abstract
Mutations stimulate evolutionary change and lead to birth defects and cancer in humans as well as to antibiotic resistance in bacteria. According to the classic view, most mutations arise in dividing cells and result from uncorrected errors of S-phase DNA replication, which is highly accurate because of the involvement of selective DNA polymerases and efficient error-correcting mechanisms. In contrast, studies in bacteria and yeast reveal that DNA synthesis associated with repair of double-strand chromosomal breaks (DSBs) by homologous recombination is highly inaccurate, thus making DSBs and their repair an important source of mutations. Different error-prone mechanisms appear to operate in different repair scenarios. In the filling in of single-stranded DNA regions, error-prone translesion DNA polymerases appear to produce most errors. In contrast, in gene conversion gap repair and in break-induced replication, errors are independent of translesion polymerases, and many mutations have the signatures of template switching during DNA repair synthesis. DNA repair also appears to create complex copy-number variants. Overall, homologous recombination, which is traditionally considered a safe pathway of DSB repair, is an important source of mutagenesis that may contribute to human disease and evolution.
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Affiliation(s)
- Anna Malkova
- Department of Biology, School of Science, IUPUI, Indianapolis, Indiana 46202-5132, USA.
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42
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Bentsen IB, Nielsen I, Lisby M, Nielsen HB, Gupta SS, Mundbjerg K, Andersen AH, Bjergbaek L. MRX protects fork integrity at protein-DNA barriers, and its absence causes checkpoint activation dependent on chromatin context. Nucleic Acids Res 2013; 41:3173-89. [PMID: 23376930 PMCID: PMC3597703 DOI: 10.1093/nar/gkt051] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
To address how eukaryotic replication forks respond to fork stalling caused by strong non-covalent protein-DNA barriers, we engineered the controllable Fob-block system in Saccharomyces cerevisiae. This system allows us to strongly induce and control replication fork barriers (RFB) at their natural location within the rDNA. We discover a pivotal role for the MRX (Mre11, Rad50, Xrs2) complex for fork integrity at RFBs, which differs from its acknowledged function in double-strand break processing. Consequently, in the absence of the MRX complex, single-stranded DNA (ssDNA) accumulates at the rDNA. Based on this, we propose a model where the MRX complex specifically protects stalled forks at protein-DNA barriers, and its absence leads to processing resulting in ssDNA. To our surprise, this ssDNA does not trigger a checkpoint response. Intriguingly, however, placing RFBs ectopically on chromosome VI provokes a strong Rad53 checkpoint activation in the absence of Mre11. We demonstrate that proper checkpoint signalling within the rDNA is restored on deletion of SIR2. This suggests the surprising and novel concept that chromatin is an important player in checkpoint signalling.
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Affiliation(s)
- Iben B Bentsen
- Department of Molecular Biology and Genetics, University of Aarhus, Aarhus 8000, Denmark.
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43
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Pedersen JM, Fredsoe J, Roedgaard M, Andreasen L, Mundbjerg K, Kruhøffer M, Brinch M, Schierup MH, Bjergbaek L, Andersen AH. DNA Topoisomerases maintain promoters in a state competent for transcriptional activation in Saccharomyces cerevisiae. PLoS Genet 2012; 8:e1003128. [PMID: 23284296 PMCID: PMC3527272 DOI: 10.1371/journal.pgen.1003128] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Accepted: 10/15/2012] [Indexed: 11/19/2022] Open
Abstract
To investigate the role of DNA topoisomerases in transcription, we have studied global gene expression in Saccharomyces cerevisiae cells deficient for topoisomerases I and II and performed single-gene analyses to support our findings. The genome-wide studies show a general transcriptional down-regulation upon lack of the enzymes, which correlates with gene activity but not gene length. Furthermore, our data reveal a distinct subclass of genes with a strong requirement for topoisomerases. These genes are characterized by high transcriptional plasticity, chromatin regulation, TATA box presence, and enrichment of a nucleosome at a critical position in the promoter region, in line with a repressible/inducible mode of regulation. Single-gene studies with a range of genes belonging to this group demonstrate that topoisomerases play an important role during activation of these genes. Subsequent in-depth analysis of the inducible PHO5 gene reveals that topoisomerases are essential for binding of the Pho4p transcription factor to the PHO5 promoter, which is required for promoter nucleosome removal during activation. In contrast, topoisomerases are dispensable for constitutive transcription initiation and elongation of PHO5, as well as the nuclear entrance of Pho4p. Finally, we provide evidence that topoisomerases are required to maintain the PHO5 promoter in a superhelical state, which is competent for proper activation. In conclusion, our results reveal a hitherto unknown function of topoisomerases during transcriptional activation of genes with a repressible/inducible mode of regulation. Gene expression is controlled at many different levels to assure appropriate responses to internal and environmental changes. The effect of topological changes in the DNA double helix on gene transcription in vivo is a poorly understood factor in the regulation of eukaryotic gene expression. Topological changes are constantly generated by DNA tracking processes and may influence gene expression if not constantly removed by DNA topoisomerases. For decades it has been generally accepted that these enzymes regulate transcription by removing excess topological strain generated during tracking of the RNA polymerase, but we still lack a more holistic view of how these enzymes influence gene transcription in their native environment. Here, we examine both global and gene-specific changes in transcription following lack of DNA topoisomerases in budding yeast. Taken together, our findings show that topoisomerases play a profound role during transcriptional activation of genes with a repressible/inducible mode of regulation. For the PHO5 gene, which is investigated in more detail, we demonstrate that topoisomerases are required for binding of a transcription factor, which is crucial for promoter opening during PHO5 activation. Our data thus suggest that inducible gene promoters are highly sensitive to changes in DNA superhelicity.
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Affiliation(s)
- Jakob Madsen Pedersen
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Jacob Fredsoe
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Morten Roedgaard
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Lotte Andreasen
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | | | | | - Marie Brinch
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Mikkel Heide Schierup
- Bioinformatics Research Center, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Lotte Bjergbaek
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Anni Hangaard Andersen
- Laboratory of Genome Research, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
- * E-mail:
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44
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Dion V, Kalck V, Horigome C, Towbin BD, Gasser SM. Increased mobility of double-strand breaks requires Mec1, Rad9 and the homologous recombination machinery. Nat Cell Biol 2012; 14:502-9. [PMID: 22484486 DOI: 10.1038/ncb2465] [Citation(s) in RCA: 236] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 02/14/2012] [Indexed: 01/13/2023]
Abstract
Chromatin mobility is thought to facilitate homology search during homologous recombination and to shift damage either towards or away from specialized repair compartments. However, unconstrained mobility of double-strand breaks could also promote deleterious chromosomal translocations. Here we use live time-lapse fluorescence microscopy to track the mobility of damaged DNA in budding yeast. We found that a Rad52-YFP focus formed at an irreparable double-strand break moves in a larger subnuclear volume than the undamaged locus. In contrast, Rad52-YFP bound at damage arising from a protein-DNA adduct shows no increase in movement. Mutant analysis shows that enhanced double-strand-break mobility requires Rad51, the ATPase activity of Rad54, the ATR homologue Mec1 and the DNA-damage-response mediator Rad9. Consistent with a role for movement in the homology-search step of homologous recombination, we show that recombination intermediates take longer to form in cells lacking Rad9.
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Affiliation(s)
- Vincent Dion
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
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Silva S, Gallina I, Eckert-Boulet N, Lisby M. Live cell microscopy of DNA damage response in Saccharomyces cerevisiae. Methods Mol Biol 2012; 920:433-443. [PMID: 22941621 DOI: 10.1007/978-1-61779-998-3_30] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Fluorescence microscopy of the DNA damage response in living cells stands out from many other DNA repair assays by its ability to monitor the response to individual DNA lesions in single cells. This is particularly true in yeast, where the frequency of spontaneous DNA lesions is relatively low compared to organisms with much larger genomes such as mammalian cells. Single cell analysis of individual DNA lesions allows specific events in the DNA damage response to be correlated with cell morphology, cell cycle phase, and other specific characteristics of a particular cell. Moreover, fluorescence live cell imaging allows for multiple cellular markers to be monitored over several hours. This chapter reviews useful fluorescent markers and genotoxic agents for studying the DNA damage response in living cells and provides protocols for live cell imaging, time-lapse microscopy, and for induction of site-specific DNA lesions.
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Affiliation(s)
- Sonia Silva
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
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Nielsen I, Andersen AH, Bjergbæk L. Studying repair of a single protein-bound nick in vivo using the Flp-nick system. Methods Mol Biol 2012; 920:393-415. [PMID: 22941619 DOI: 10.1007/978-1-61779-998-3_28] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The Flp-nick system is a simple in vivo system developed for studying the cellular responses to a protein-bound nick at a single genomic site in the budding yeast Saccharomyces cerevisiae. The Flp-nick system takes advantage of a mutant Flp recombinase that can introduce a nick at a specific Flp recombinase recognition target (FRT) site, which has been integrated into the yeast genome. Upon cleavage at the FRT site, the Flp mutant becomes covalently linked to the 3' DNA end at the nick in an irreversible manner, as the mutant fails to accomplish the required religation process. Thus, the established damage mimics a stabilized topoisomerase I-DNA cleavage complex. DNA topoisomerases are ubiquitous enzymes that relieve topological stress in the DNA arising during DNA replication or transcription. During this process, they make transient enzyme-DNA cleavage complexes, which normally are reversed by a rapid ligation step. However, aberrant long-lived enzyme-DNA complexes may occur frequently due to either endogenous or exogenous damage, and the cellular repair machinery therefore needs to be able to eliminate this type of damage. This chapter describes how to establish the Flp-nick system in S. cerevisiae, how to detect FlpH305L at the FRT site using a modified chromatin immunoprecipitation assay where formaldehyde fixation is omitted, and how to monitor nicking at the FRT site by alkaline denaturing gel analysis.
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Affiliation(s)
- Ida Nielsen
- Department of Molecular Biology and Genetics, University of Aarhus, Aarhus, Denmark
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Leung GP, Lee L, Schmidt TI, Shirahige K, Kobor MS. Rtt107 is required for recruitment of the SMC5/6 complex to DNA double strand breaks. J Biol Chem 2011; 286:26250-7. [PMID: 21642432 DOI: 10.1074/jbc.m111.235200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Genome integrity is maintained by a network of DNA damage response pathways, including checkpoints and DNA repair processes. In Saccharomyces cerevisiae, the BRCT domain-containing protein Rtt107/Esc4 is required for the restart of DNA replication after successful repair of DNA damage and for cellular resistance to DNA-damaging agents. In addition to its well characterized interaction with the endonuclease Slx4, Rtt107 interacts with a number of other DNA repair and recombination proteins. These include the evolutionarily conserved SMC5/6 complex, which is involved in numerous chromosome maintenance activities, such as DNA repair, chromosome segregation, and telomere function. The interaction between Rtt107 and the SMC5/6 complex was mediated through the N-terminal BRCT domains of Rtt107 and the Nse6 subunit of SMC5/6 and was independent of methyl methane sulfonate-induced damage and Slx4. Supporting a shared function in the DNA damage response, Rtt107 was required for recruitment of SMC5/6 to DNA double strand breaks. However, this functional relationship did not extend to other types of DNA lesions such as protein-bound nicks. Interestingly, Rtt107 was phosphorylated when SMC5/6 function was compromised in the absence of DNA-damaging agents, indicating a connection beyond the DNA damage response. Genetic analyses revealed that, although a subset of Rtt107 and SMC5/6 functions was shared, these proteins also contributed independently to maintenance of genome integrity.
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Affiliation(s)
- Grace P Leung
- Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada
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