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Sagi T, Sadato D, Takayasu K, Sasanuma H, Kanoh Y, Masai H. RNA-DNA hybrids on protein coding genes are stabilized by loss of RNase H and are associated with DNA damages during S-phase in fission yeast. Genes Cells 2024. [PMID: 39252397 DOI: 10.1111/gtc.13157] [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: 07/13/2024] [Revised: 08/15/2024] [Accepted: 08/23/2024] [Indexed: 09/11/2024]
Abstract
RNA-DNA hybrid is a part of the R-loop which is an important non-standard nucleic acid structure. RNA-DNA hybrid/R-loop causes genomic instability by inducing DNA damages or inhibiting DNA replication. It also plays biologically important roles in regulation of transcription, replication, recombination and repair. Here, we have employed catalytically inactive human RNase H1 mutant (D145N) to visualize RNA-DNA hybrids and map their genomic locations in fission yeast cells. The RNA-DNA hybrids appear as multiple nuclear foci in rnh1∆rnh201∆ cells lacking cellular RNase H activity, but not in the wild-type. The majority of RNA-DNA hybrid loci are detected at the protein coding regions and tRNA. In rnh1∆rnh201∆ cells, cells with multiple Rad52 foci increase during S-phase and about 20% of the RNA-DNA hybrids overlap with Rad52 loci. During S-phase, more robust association of Rad52 with RNA-DNA hybrids was observed in the protein coding region than in M-phase. These results suggest that persistent RNA-DNA hybrids in the protein coding region in rnh1∆rnh201∆ cells generate DNA damages during S-phase, potentially through collision with DNA replication forks.
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Affiliation(s)
- Tomoko Sagi
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Daichi Sadato
- Clinical Research and Trials Center, Tokyo Metropolitan Cancer and Infectious Diseases Center, Komagome Hospital, Tokyo, Japan
| | - Kazuto Takayasu
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
- Department of Biosciences, School of Science, Kitasato University, Sagamihara, Kanagawa, Japan
| | - Hiroyuki Sasanuma
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Yutaka Kanoh
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Hisao Masai
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
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2
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Davé A, Pai CC, Durley SC, Hulme L, Sarkar S, Wee BY, Prudden J, Tinline-Purvis H, Cullen JK, Walker C, Watson A, Carr AM, Murray JM, Humphrey TC. Homologous recombination repair intermediates promote efficient de novo telomere addition at DNA double-strand breaks. Nucleic Acids Res 2020; 48:1271-1284. [PMID: 31828313 PMCID: PMC7026635 DOI: 10.1093/nar/gkz1109] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Revised: 10/23/2019] [Accepted: 12/03/2019] [Indexed: 12/11/2022] Open
Abstract
The healing of broken chromosomes by de novo telomere addition, while a normal developmental process in some organisms, has the potential to cause extensive loss of heterozygosity, genetic disease, or cell death. However, it is unclear how de novo telomere addition (dnTA) is regulated at DNA double-strand breaks (DSBs). Here, using a non-essential minichromosome in fission yeast, we identify roles for the HR factors Rqh1 helicase, in concert with Rad55, in suppressing dnTA at or near a DSB. We find the frequency of dnTA in rqh1Δ rad55Δ cells is reduced following loss of Exo1, Swi5 or Rad51. Strikingly, in the absence of the distal homologous chromosome arm dnTA is further increased, with nearly half of the breaks being healed in rqh1Δ rad55Δ or rqh1Δ exo1Δ cells. These findings provide new insights into the genetic context of highly efficient dnTA within HR intermediates, and how such events are normally suppressed to maintain genome stability.
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Affiliation(s)
- Anoushka Davé
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Sussex BN1 9RQ, UK
| | - Chen-Chun Pai
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - Samuel C Durley
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Sussex BN1 9RQ, UK
| | - Lydia Hulme
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - Sovan Sarkar
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - Boon-Yu Wee
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - John Prudden
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - Helen Tinline-Purvis
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - Jason K Cullen
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
- QIMR Berghofer Medical Research Institute, Brisbane 4006, Australia
| | - Carol Walker
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | - Adam Watson
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Sussex BN1 9RQ, UK
| | - Antony M Carr
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Sussex BN1 9RQ, UK
| | - Johanne M Murray
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Sussex BN1 9RQ, UK
| | - Timothy C Humphrey
- CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
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3
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The RecQ DNA helicase Rqh1 constrains Exonuclease 1-dependent recombination at stalled replication forks. Sci Rep 2016; 6:22837. [PMID: 26957021 PMCID: PMC4783781 DOI: 10.1038/srep22837] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 02/22/2016] [Indexed: 01/28/2023] Open
Abstract
DNA double-strand break (DSB) repair by homologous recombination (HR) involves resection of the break to expose a 3' single-stranded DNA tail. In budding yeast, resection occurs in two steps: initial short-range resection, performed by Mre11-Rad50-Xrs2 and Sae2; and long-range resection catalysed by either Exo1 or Sgs1-Dna2. Here we use genetic assays to investigate the importance of Exo1 and the Sgs1 homologue Rqh1 for DNA repair and promotion of direct repeat recombination in the fission yeast Schizosaccharomyces pombe. We find that Exo1 and Rqh1 function in alternative redundant pathways for promoting survival following replication fork breakage. Exo1 promotes replication fork barrier-induced direct repeat recombination but intriguingly limits recombination induced by fork breakage. Direct repeat recombination induced by ultraviolet light depends on either Exo1 or Rqh1. Finally, we show that Rqh1 plays a major role in limiting Exo1-dependent direct repeat recombination induced by replication fork stalling but only a minor role in constraining recombination induced by fork breakage. The implications of our findings are discussed in the context of the benefits that long-range resection may bring to processing perturbed replication forks.
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4
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Role of Blm and collaborating factors in recombination and survival following replication stress in Ustilago maydis. DNA Repair (Amst) 2009; 8:752-9. [PMID: 19349216 DOI: 10.1016/j.dnarep.2009.02.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 01/16/2009] [Accepted: 02/06/2009] [Indexed: 11/20/2022]
Abstract
Inactivation of the structural gene for the RecQ family member, BLM in human, Sgs1 in budding yeast, or Rqh1 in fission yeast leads to inappropriate recombination, chromosome abnormalities, and disturbed replication fork progression. Studies with yeasts have demonstrated that auxiliary gene functions can contribute in overlapping ways with Sgs1 or Rqh1 to circumvent or overcome lesions in DNA caused by certain genotoxic agents. In the combined absence of these functions, recombination-mediated processes lead to severe loss of fitness. Here we performed a genetic study to determine the role of the Ustilago maydis Blm homolog in DNA repair and in alleviating replication stress. We characterized the single mutant as well as double mutants additionally deleted of genes encoding Srs2, Fbh1, Mus81, or Exo1. Unlike yeasts, neither the blm srs2, blm exo1, nor blm mus81 double mutant exhibited extreme loss of fitness. Inactivation of Brh2, the BRCA2 homolog, suppressed toxicity to hydroxyurea caused by loss of Blm function. However, differential suppression by Brh2 derivatives lacking the canonical DNA-binding region suggests that the particular domain structure comprising this DNA-binding region may be instrumental in promoting the observed hydroxyurea toxicity.
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5
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Hope JC, Cruzata LD, Duvshani A, Mitsumoto J, Maftahi M, Freyer GA. Mus81-Eme1-dependent and -independent crossovers form in mitotic cells during double-strand break repair in Schizosaccharomyces pombe. Mol Cell Biol 2007; 27:3828-38. [PMID: 17353272 PMCID: PMC1900003 DOI: 10.1128/mcb.01596-06] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2006] [Revised: 09/18/2006] [Accepted: 03/02/2007] [Indexed: 11/20/2022] Open
Abstract
During meiosis, double-strand breaks (DSBs) lead to crossovers, thought to arise from the resolution of double Holliday junctions (HJs) by an HJ resolvase. In Schizosaccharomyces pombe, meiotic crossovers are produced primarily through a mechanism requiring the Mus81-Eme1 endonuclease complex. Less is known about the processes that produces crossovers during the repair of DSBs in mitotic cells. We employed an inducible DSB system to determine the role of Rqh1-Top3 and Mus81-Eme1 in mitotic DSB repair and crossover formation in S. pombe. In agreement with the meiotic data, crossovers are suppressed in cells lacking Mus81-Eme1. And relative to the wild type, rqh1Delta cells show a fourfold increase in crossover frequency. This suppression of crossover formation by Rqh1 is dependent on its helicase activity. We found that the synthetic lethality of cells lacking both Rqh1 and Eme1 is suppressed by loss of swi5(+), which allowed us to show that the excess crossovers formed in an rqh1Delta background are independent of Mus81-Eme1. This result suggests that a second process for crossover formation exists in S. pombe and is consistent with our finding that deletion of swi5(+) restored meiotic crossovers in eme1Delta cells. Evidence suggesting that Rqh1 also acts downstream of Swi5 in crossover formation was uncovered in these studies. Our results suggest that during Rhp51-dependent repair of DSBs, Rqh1-Top3 suppresses crossovers in the Rhp57-dependent pathway while Mus81-Eme1 and possibly Rqh1 promote crossovers in the Swi5-dependent pathway.
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Affiliation(s)
- Justin C Hope
- Graduate Program in Anatomy and Cell Biology, Columbia University, 722 W. 168th Street, New York, NY 10032, USA
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6
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Raji H, Hartsuiker E. Double-strand break repair and homologous recombination in Schizosaccharomyces pombe. Yeast 2007; 23:963-76. [PMID: 17072889 DOI: 10.1002/yea.1414] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The study of double-strand break repair and homologous recombination in Saccharomyces cerevisiae meiosis has provided important information about the mechanisms involved. However, it has become clear that the resulting recombination models are only partially applicable to repair in mitotic cells, where crossover formation is suppressed. In recent years our understanding of double-strand break repair and homologous recombination in Schizosaccharomyces pombe has increased significantly, and the identification of novel pathways and genes with homologues in higher eukaryotes has increased its value as a model organism for double-strand break repair. In this review we will focus on the involvement of homologous recombination and repair in different aspects of genome stability in Sz. pombe meiosis, replication and telomere maintenance. We will also discuss anti-recombination pathways (that suppress crossover formation), non-homologous end-joining, single-strand annealing and factors that influence the choice and prevalence of the different repair pathways in Sz. pombe.
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Affiliation(s)
- Hayatu Raji
- Genome Damage and Stability Centre, University of Sussex, Brighton BN1 9RQ, UK
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7
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Lo YC, Paffett KS, Amit O, Clikeman JA, Sterk R, Brenneman MA, Nickoloff JA. Sgs1 regulates gene conversion tract lengths and crossovers independently of its helicase activity. Mol Cell Biol 2006; 26:4086-94. [PMID: 16705162 PMCID: PMC1489077 DOI: 10.1128/mcb.00136-06] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
RecQ helicases maintain genome stability and suppress tumors in higher eukaryotes through roles in replication and DNA repair. The yeast RecQ homolog Sgs1 interacts with Top3 topoisomerase and Rmi1. In vitro, Sgs1 binds to and branch migrates Holliday junctions (HJs) and the human RecQ homolog BLM, with Top3alpha, resolves synthetic double HJs in a noncrossover sense. Sgs1 suppresses crossovers during the homologous recombination (HR) repair of DNA double-strand breaks (DSBs). Crossovers are associated with long gene conversion tracts, suggesting a model in which Sgs1 helicase catalyzes reverse branch migration and convergence of double HJs for noncrossover resolution by Top3. Consistent with this model, we show that allelic crossovers and gene conversion tract lengths are increased in sgs1Delta. However, crossover and tract length suppression was independent of Sgs1 helicase activity, which argues against helicase-dependent HJ convergence. HJs may converge passively by a "random walk," and Sgs1 may play a structural role in stimulating Top3-dependent resolution. In addition to the new helicase-independent functions for Sgs1 in crossover and tract length control, we define three new helicase-dependent functions, including the suppression of chromosome loss, chromosome missegregation, and synthetic lethality in srs2Delta. We propose that Sgs1 has helicase-dependent functions in replication and helicase-independent functions in DSB repair by HR.
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Affiliation(s)
- Yi-Chen Lo
- Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
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8
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Hope JC, Mense SM, Jalakas M, Mitsumoto J, Freyer GA. Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity. Proc Natl Acad Sci U S A 2006; 103:5875-80. [PMID: 16595622 PMCID: PMC1458666 DOI: 10.1073/pnas.0601571103] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Many questions remain about the process of DNA double strand break (DSB) repair by homologous recombination (HR), particularly concerning the exact function played by individual proteins and the details of specific steps in this process. Some recent studies have shown that RecQ DNA helicases have a function in HR. We studied the role of the RecQ helicase Rqh1 with HR proteins in the repair of a DSB created at a unique site within the Schizosaccharomyces pombe genome. We found that DSBs in rqh1(+) cells, are predominantly repaired by interchromosomal gene conversion, with HR between sister chromatids [sister-chromatid conversion (SCC)], occurring less frequently. In Deltarqh1 cells, repair by SCC is favored, and gene conversion rates slow significantly. When we limited the potential for SCC in Deltarqh1 cells by reducing the length of the G2 phase of the cell cycle, DSB repair continued to be predominated by SCC, whereas it was essentially eliminated in wild-type cells. These data indicate that Rqh1 acts to regulate DSB repair by blocking SCC. Interestingly, we found that this role for Rqh1 is independent of its helicase activity. In the course of these studies, we also found nonhomologous end joining to be largely faithful in S. pombe, contrary to current belief. These findings provide insight into the regulation of DSB repair by RecQ helicases.
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Affiliation(s)
| | - Sarah M. Mense
- Graduate Program in Environmental Health Sciences, Columbia University, Kolb Building Room 140, 722 West 168th Street, New York, NY 10032
| | - Merle Jalakas
- Graduate Program in Environmental Health Sciences, Columbia University, Kolb Building Room 140, 722 West 168th Street, New York, NY 10032
| | - Jun Mitsumoto
- Graduate Program in Environmental Health Sciences, Columbia University, Kolb Building Room 140, 722 West 168th Street, New York, NY 10032
| | - Greg A. Freyer
- *Graduate Program in Anatomy and Cell Biology and
- To whom correspondence should be addressed. E-mail:
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9
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Hartung F, Puchta H. The RecQ gene family in plants. JOURNAL OF PLANT PHYSIOLOGY 2006; 163:287-96. [PMID: 16371241 DOI: 10.1016/j.jplph.2005.10.013] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Accepted: 10/15/2005] [Indexed: 05/05/2023]
Abstract
RecQ helicases are conserved throughout all kingdoms of life regarding their overall structure and function. They are 3'-5' DNA helicases resolving different recombinogenic DNA structures. The RecQ helicases are key factors in a number of DNA repair and recombination pathways involved in the maintenance of genome integrity. In eukaryotes the number of RecQ genes and the structure of RecQ proteins vary strongly between organisms. Therefore, they have been named RecQ-like genes. Knockouts of several RecQ-like genes cause severe diseases in animals or harmful cellular phenotypes in yeast. Until now the largest number of RecQ-like genes per organism has been found in plants. Arabidopsis and rice possess seven different RecQ-like genes each. In the almost completely sequenced genome of the moss Physcomitrella patens at least five RecQ-like genes are present. One of the major present and future research aims is to define putative plant-specific functions and to assign their roles in DNA repair and recombination pathways in relation to RecQ genes from other eukaryotes. Regarding their intron positions, the structures of six RecQ-like genes of dicots and monocots are virtually identical indicating a conservation over a time scale of 150 million years. In contrast to other eukaryotes one gene (RecQsim) exists exclusively in plants. It possesses an interrupted helicase domain but nevertheless seems to have maintained the RecQ function. Owing to a recent gene duplication besides the AtRecQl4A gene an additional RecQ-like gene (AtRecQl4B) exists in the Brassicaceae only. Genetic studies indicate that a AtRecQl4A knockout results in sensitivity to mutagens as well as an hyper-recombination phenotype. Since AtRecQl4B was still present, both genes must have non-redundant roles. Analysis of plant RecQ-like genes will not only increase the knowledge on DNA repair and recombination, but also on the evolution and radiation of protein families.
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Affiliation(s)
- Frank Hartung
- Botanisches Institut II, Universität Karlsruhe (TH), Kaiserstr. 12, 76128 Karlsruhe, Germany.
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10
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Ahmad F, Stewart E. The N-terminal region of the Schizosaccharomyces pombe RecQ helicase, Rqh1p, physically interacts with Topoisomerase III and is required for Rqh1p function. Mol Genet Genomics 2005; 273:102-14. [PMID: 15702347 DOI: 10.1007/s00438-005-1111-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2004] [Accepted: 01/03/2005] [Indexed: 11/29/2022]
Abstract
The Schizosaccharomyces pombe rqh1+ gene encodes a member of the RecQ DNA helicase family. Members of this protein family are essential for the maintenance of genetic integrity. Thus, mutations in the genes encoding the human RecQ homologues Blm, Wrn and RecQ4 cause Bloom syndrome, Werner syndrome and Rothmund-Thomson syndrome, respectively-diseases which result from genome instability. S. pombe cells that lack a functional rqh1+ gene show reduced viability and display defective chromosome segregation, particularly after UV irradiation or S-phase arrest. In this study we used an rqh1+ deletion series to show that the N-terminal portion of Rqh1 is essential for Rqh1 function. Moreover, the conserved Helicase and RNaseD C-terminal (HRDC) domain of Rqh1 also plays a role in allowing cells to tolerate exposure to DNA damaging agents and the S-phase inhibitor hydroxyurea (HU). We also demonstrate that Topoisomerase III (Top3) binds to a site within the first 322 N-terminal amino acids of Rqh1 and that this binding correlates with Rqh1 function. Genetic analysis of rqh1- top3delta mutants reveals that, in the presence of functional or partially functional Rqh1 protein, Top3 is required to maintain genome integrity and cell viability.
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Affiliation(s)
- Fouzia Ahmad
- School of Biological Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester, M13 9PT, UK.
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11
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Rockmill B, Fung JC, Branda SS, Roeder GS. The Sgs1 helicase regulates chromosome synapsis and meiotic crossing over. Curr Biol 2004; 13:1954-62. [PMID: 14614820 DOI: 10.1016/j.cub.2003.10.059] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
BACKGROUND In budding yeast, Sgs1 is the sole member of the RecQ family of DNA helicases. Like the human Bloom syndrome helicase (BLM), Sgs1 functions during both vegetative growth and meiosis. The sgs1 null mutant sporulates poorly and displays reduced spore viability. RESULTS We have identified novel functions for Sgs1 in meiosis. Loss of Sgs1 increases the number of axial associations, which are connections between homologous chromosomes that serve as initiation sites for synaptonemal complex formation. In addition, mutation of SGS1 increases the number of synapsis initiation complexes and increases the rate of chromosome synapsis. Loss of Sgs1 also increases the number of meiotic crossovers without changing the frequency of gene conversion. The sgs1 defect in sporulation is due to checkpoint-induced arrest/delay at the pachytene stage of meiotic prophase. A non-null allele of SGS1 that specifically deletes the helicase domain is defective in the newly described meiotic functions of Sgs1, but wild-type for most vegetative functions and for spore formation. CONCLUSIONS We have shown that the helicase domain of Sgs1 serves as a negative regulator of meiotic interchromosomal interactions. The activity of the wild-type Sgs1 protein reduces the numbers of axial associations, synapsis initiation complexes, and crossovers, and decreases the rate of chromosome synapsis. Our data argue strongly that axial associations marked by synapsis initiation complexes correspond to sites of reciprocal exchange. We propose that the Sgs1 helicase prevents a subset of recombination intermediates from becoming crossovers, and this distinction is made at an early stage in meiotic prophase.
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Affiliation(s)
- Beth Rockmill
- Howard Hughes Medical Institute, Yale University, P.O. Box 208103, New Haven, 06520 CT, USA
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12
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Bachrati CZ, Hickson ID. RecQ helicases: suppressors of tumorigenesis and premature aging. Biochem J 2003; 374:577-606. [PMID: 12803543 PMCID: PMC1223634 DOI: 10.1042/bj20030491] [Citation(s) in RCA: 302] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2003] [Revised: 06/10/2003] [Accepted: 06/12/2003] [Indexed: 02/04/2023]
Abstract
The RecQ helicases represent a subfamily of DNA helicases that are highly conserved in evolution. Loss of RecQ helicase function leads to a breakdown in the maintenance of genome integrity, in particular hyper-recombination. Germ-line defects in three of the five known human RecQ helicases give rise to defined genetic disorders associated with cancer predisposition and/or premature aging. These are Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome, which are caused by defects in the genes BLM, WRN and RECQ4 respectively. Here we review the properties of RecQ helicases in organisms from bacteria to humans, with an emphasis on the biochemical functions of these enzymes and the range of protein partners that they operate with. We will discuss models in which RecQ helicases are required to protect against replication fork demise, either through prevention of fork breakdown or restoration of productive DNA synthesis.
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Affiliation(s)
- Csanád Z Bachrati
- Cancer Research UK Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
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13
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Bernstein DA, Keck JL. Domain mapping of Escherichia coli RecQ defines the roles of conserved N- and C-terminal regions in the RecQ family. Nucleic Acids Res 2003; 31:2778-85. [PMID: 12771204 PMCID: PMC156711 DOI: 10.1093/nar/gkg376] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
RecQ DNA helicases function in DNA replication, recombination and repair. Although the precise cellular roles played by this family of enzymes remain elusive, the importance of RecQ proteins is clear; mutations in any of three human RecQ genes lead to genomic instability and cancer. In this report, proteolysis is used to define a two-domain structure for Escherichia coli RecQ, revealing a large (approximately 59 kDa) N-terminal and a small (approximately 9 kDa) C-terminal domain. A short N-terminal segment (7 or 21 residues) is also shown to be sensitive to proteases. The effects of removing these regions of RecQ are tested in vitro. Removing 21 N-terminal residues from RecQ severely diminishes its DNA-dependent ATPase and helicase activities, but does not affect its ability to bind DNA in electrophoretic mobility shift assays. In contrast, removing the approximately 9 kDa C-terminal domain from RecQ results in a fragment with normal levels of ATPase and helicase activity, but that has lost the ability to stably associate with DNA. These results establish the biochemical roles of an N-terminal sequence motif in RecQ catalytic function and for the C-terminal RecQ domain in stable DNA binding.
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Affiliation(s)
- Douglas A Bernstein
- Department of Biomolecular Chemistry, 550 Medical Science Center, 1300 University Avenue, University of Wisconsin, Madison, WI 53706-1532, USA
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14
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Current awareness on yeast. Yeast 2003; 20:273-80. [PMID: 12622058 DOI: 10.1002/yea.942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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