Homologous recombination is responsible for cell death in the absence of the Sgs1 and Srs2 helicases

Abstract

DNA helicases are involved in many aspects of DNA metabolism, including transcription, replication, recombination and repair. In the yeast Saccharomyces cerevisiae, the absence of the Sgs1 helicase results in genomic instability and accelerated ageing. In human cells, mutations in orthologues of SGS1 lead to Bloom (BS), Werner (WS) or Rothmund-Thomson (RTS) syndromes, which are rare, autosomal recessive diseases characterized by genetic instability associated with cancer predisposition. Although data concerning these human diseases are accumulating, there is still no clear idea of the function of the proteins involved. Here we show that sgs1Delta mutants are deficient in DNA repair and are defective for induced recombination events that involve homologous chromosomes. The role of homologous recombination is further evidenced in haploid cells in which both Sgs1p and Srs2p are absent. Yeast SRS2 encodes another DNA helicase involved in the maintenance of genome integrity. Our data suggest that some defects observed in BS, WS or RTS are the consequence of unrestrained recombination.

Genetic evidence for a role of Saccharomyces cerevisiae Mph1 in recombinational DNA repair under replicative stress

“…Srs2 probably favours resolution via the Mms4/Mus81-Mph1 pathway. SGS1 's ability to partially rescue camptothecin sensitivity of srs2 and mph1 srs2 mutants, the sgs1 srs2, sgs1 mus81 (Gangloff et al, 2000;Fabre et al, 2002) and mph1 srs2 defects, support the model.…”

Regulation of Recombination and Genomic Maintenance

“…For example, ectopic recombination between repeated DNA is a potent driver of chromosomal rearrangements, as suspected from genomic analysis and established in genetic model systems (Szankasi et al 1986;Cooper et al 1997;Agarwal et al 2006;Haber 2006;Weinstock et al 2006;Putnam et al 2009;Song et al 2014). Furthermore, the identification of synthetic lethality in double mutants that depend on HR, called recombination-dependent lethality, shows that uncontrolled HR leads to potentially toxic intermediates and cell death (Heude et al 1995;Schild 1995;Gangloff et al 2000;Fabre et al 2002;Bastin-Shanower et al 2003).…”

Shu Proteins Promote the Formation of Homologous Recombination Intermediates That Are Processed by Sgs1-Rmi1-Top3

“…Indeed, Bloom's syndrome cells classically demonstrate elevated levels of sister chromatid exchanges, mitotic recombination, and genome instability. Mutation of the BLM, hTOPOIII␣, or hRMI1 homologues in Saccharomyces cerevisiae (SGS1, TOP3, or RMI1, respectively) similarly causes sensitivity to genotoxic agents, hyper-recombination, and synthetic lethality with mutations in other genes also implicated in HRR (e.g., MUS81 and SRS2; Gangloff et al, 1994;Watt et al, 1996;Gangloff et al, 2000;Mullen et al, 2001;Fabre et al, 2002;Chang et al, 2005;Mullen et al, 2005). Furthermore, unresolved HRR intermediates have been directly visualized by two-dimensional (2D) gel electrophoresis in cells lacking Sgs1 or in cells with impaired Top3 function (Liberi et al, 2005;Mankouri and Hickson, 2006).…”

“…Furthermore, unresolved HRR intermediates have been directly visualized by two-dimensional (2D) gel electrophoresis in cells lacking Sgs1 or in cells with impaired Top3 function (Liberi et al, 2005;Mankouri and Hickson, 2006). Interestingly, many of the cellular/phenotypic defects observed in sgs1, top3, or rmi1 cells can be suppressed by deletion of genes that control the early steps of HRR (e.g., RAD52, RAD51, RAD55, RAD57, and RAD54; Gangloff et al, 2000;Fabre et al, 2002;Oakley et al, 2002;Shor et al, 2002;Chang et al, 2005;Mullen et al, 2005). Taken together, these observations suggest that excessive, unscheduled, or incomplete HRR can create toxic DNA repair intermediates, and highlights the requirement for cells to carefully regulate HRR during S-phase.…”