Role for the Fission Yeast RecQ Helicase in DNA Repair in G<sub>2</sub>

Laursen, Louise; Ampatzidou, Eleni; Andersen, Anders H.; Murray, Johanne M.

doi:10.1128/mcb.23.10.3692-3705.2003

Cited by 68 publications

(80 citation statements)

References 57 publications

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“…Both BLM and Sgs1 associate with Rad51 and colocalize on ssDNA after exposure to ionizing radiation (53,54). Similarly, Rqh1 foci form earlier than Rhp51 foci after UV irradiation of S. pombe cells (55). Together, these studies suggest that RecQ helicases act both early and late during HR.…”

Section: Discussionmentioning

confidence: 52%

Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity

Hope

Mense

Jalakas

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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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 ⌬rqh1 cells, repair by SCC is favored, and gene conversion rates slow significantly. When we limited the potential for SCC in ⌬rqh1 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.homologous recombination ͉ nonhomologous end joining ͉ rqh1 ͉ gene conversion D ouble strand breaks (DSBs) pose a major problem for genomic instability and cell survival, because a single unrepaired DSB is, presumably, sufficient to cause cell death (1). The sources of DSBs can be either endogenous, such as those induced during the reshuffling of DNA in Ig gene diversification, or exogenous, such as those induced by exposure to ionizing radiation (2-4). The cell has two major mechanisms for the repair of DSBs: homologous recombination (HR) and nonhomologous end joining (NHEJ), each used to varying degrees in different organisms (2,3,5,6). HR is characterized as an error-free process using homologous sequences as the template to repair the DSB. Repair by HR begins with the formation of 3Ј single strand ends at the break that can then invade homologous duplex DNA. The 3Ј end of the invading strand is extended by DNA polymerase. At this point, the DSB can be repaired by either DSB repair, which involves formation of a double Holliday junction (HJ) or synthesis-dependent strand annealing (3, 7).In NHEJ, the DNA ends are resealed by rejoining the broken ends; however, this process can lead to loss of information at the break and is, thus, referred to as error-prone repair (5,8). Whereas mammalian cells preferentially use NHEJ over HR, budding yeast, for the most part, use HR over NHEJ. In Saccharomyces cerevisiae, the MRX (MRN in Schizosaccharomyces pombe) complex has been shown to play a role in NHEJ (9, 10). In S. pombe, only pKu70͞80 and Ligase IV have been identified as functioning in NHEJ, and MRN does not appear to be active in this process (11).RecQ DNA helicases are found in vi...

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Section: Discussionmentioning

confidence: 52%

Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity

Hope

Mense

Jalakas

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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“…Similarly, the slow-growth phenotype of top3 strains is relieved in cells lacking any of the RAD52 epistasis genes that are required for homologous recombination (HR). Such interactions are also observed in S. pombe where the inviability of top3 strains is relieved by eliminating some HR functions (Gangloff et al 2000;Maftahi et al 2002;Oakley et al 2002;Shor et al 2002) and the UV sensitivity of rqh1 cells is suppressed in strains lacking HR (Laursen et al 2003).…”

Section: Introductionmentioning

confidence: 78%

Roles of SGS1, MUS81, and RAD51 in the repair of lagging-strand replication defects in Saccharomyces cerevisiae

Miki¹,

Brill²

2005

Curr Genet

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Yeast cells lacking the SGS1 DNA helicase and the MUS81 structure-specific endonuclease display a synthetic lethality that is suppressed by loss of the RAD51 recombinase. This epistatic interaction suggests that the primary function of SGS1 or MUS81, or both genes, is downstream of RAD51. To identify RAD51-independent functions of SGS1 and MUS81, a synthetic-lethal screen was performed on the sgs1 mus81 rad51 triple mutant. We found that mutation of RNH202, which encodes a subunit of the hetero-trimeric RNase H2, generates a profound synthetic-sickness in this background. RNase H2 is thought to play a non-essential role in Okazaki fragment maturation. Cells lacking RNH202 showed synthetic growth defects when combined with either mus81 or sgs1 alone. But, whereas the loss of RAD51 had little effect on rnh202 sgs1 double mutants, it strongly inhibited the growth of rnh202 mus81 cells. These data indicate that the primary function of SGS1, but not MUS81, is downstream of RAD51. SGS1 must have some RAD51-independent function, however, since the growth of rnh202 mus8 1rad51 cells was further compromised by the loss of SGS1. Consistent with these results, we show that rnh202 cells display a sensitivity to DNA-damaging agents that is exacerbated in the absence of RAD51 or MUS81. These data support a model in which defects in lagging-strand replication are repaired by the Mus81 endonuclease or through a pathway dependent on Rad51 and Sgs1.

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“…The importance of this association was corroborated by their interaction in vitro (26,64). In budding and fission yeast mutations in sgs1 act as suppressors of the slowgrowth phenotype of top3 (17,34). It has been proposed that Top3p acts on substrates created by Sgs1p.…”

mentioning

confidence: 84%

Multiple Genetic Pathways Involving the Caenorhabditis elegans Bloom's Syndrome Genes him-6, rad-51, and top-3 Are Needed To Maintain Genome Stability in the Germ Line

Wicky

Alpi

Passannante

et al. 2004

Molecular and Cellular Biology

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Bloom's syndrome (BS) is an autosomal-recessive human disorder caused by mutations in the BS RecQ helicase and is associated with loss of genomic integrity and an increased incidence of cancer. We analyzed the mitotic and the meiotic roles of Caenorhabditis elegans him-6, which we show to encode the ortholog of the human BS gene. Mutations in him-6 result in an enhanced irradiation sensitivity, a partially defective S-phase checkpoint, and in reduced levels of DNA-damage induced apoptosis. Furthermore, him-6 mutants exhibit a decreased frequency of meiotic recombination that is probably due to a defect in the progression of crossover recombination. In mitotically proliferating germ cells, our genetic interaction studies, as well as the assessment of the number of double-strand breaks via RAD-51 foci, reveal a complex regulatory network that is different from the situation in yeast. Although the number of double-strand breaks in him-6 and top-3 single mutants is elevated, the combined depletion of him-6 and top-3 leads to mitotic catastrophe concomitant with a massive increase in the level of double-strand breaks, a phenotype that is completely suppressed by rad-51. him-6 and top-3 are thus needed to maintain low levels of double-strand breaks in normally proliferating germ cells, and both act in partial redundant pathways downstream of rad-51 to prevent mitotic catastrophy. Finally, we show that topoisomerase III␣ acts independently during a late stage of meiotic recombination.

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Role for the Fission Yeast RecQ Helicase in DNA Repair in G₂

Cited by 68 publications

References 57 publications

Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity

Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity

Roles of SGS1, MUS81, and RAD51 in the repair of lagging-strand replication defects in Saccharomyces cerevisiae

Multiple Genetic Pathways Involving the Caenorhabditis elegans Bloom's Syndrome Genes him-6, rad-51, and top-3 Are Needed To Maintain Genome Stability in the Germ Line

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Role for the Fission Yeast RecQ Helicase in DNA Repair in G2

Cited by 68 publications

References 57 publications

Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity

Rqh1 blocks recombination between sister chromatids during double strand break repair, independent of its helicase activity

Roles of SGS1, MUS81, and RAD51 in the repair of lagging-strand replication defects in Saccharomyces cerevisiae

Multiple Genetic Pathways Involving the Caenorhabditis elegans Bloom's Syndrome Genes him-6, rad-51, and top-3 Are Needed To Maintain Genome Stability in the Germ Line

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Role for the Fission Yeast RecQ Helicase in DNA Repair in G₂