Srs2 and Sgs1-Top3 suppress crossovers during double-strand break repair in yeast.
Very few gene conversions in mitotic cells are associated with crossovers, suggesting that these events are regulated. This may be important for the maintenance of genetic stability. We have analyzed the relationship between homologous recombination and crossing-over in haploid budding yeast and identified factors involved in the regulation of crossover outcomes. Gene conversions unaccompanied by a crossover appear 30 min before conversions accompanied by exchange, indicating that there are two different repair mechanisms in mitotic cells. Crossovers are rare (5%), but deleting the BLM/WRN homolog, SGS1, or the SRS2 helicase increases crossovers 2- to 3-fold. Overexpressing SRS2 nearly eliminates crossovers, whereas overexpression of RAD51 in srs2Delta cells almost completely eliminates the noncrossover recombination pathway. We suggest Sgs1 and its associated topoisomerase Top3 remove double Holliday junction intermediates from a crossover-producing repair pathway, thereby reducing crossovers. Srs2 promotes the noncrossover synthesis-dependent strand-annealing (SDSA) pathway, apparently by regulating Rad51 binding during strand exchange.
Ira
Grzegorz
G
Rosenstiel Center and Department of Biology, Brandeis University, Waltham, MA 02454, USA.
Malkova
Anna
A
Liberi
Giordano
G
Foiani
Marco
M
Haber
James E
JE
D003434:Crossing Over, Genetic; D004249:DNA Damage; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D045566:DNA, Cruciform / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D008938:Mitosis / Q000235:genetics; D051135:Rad51 Recombinase; D053484:RecQ Helicases; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
D045566:DNA, Cruciform; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C061376:SRS2 protein, S cerevisiae; C495151:RAD51 protein, S cerevisiae; D051135:Rad51 Recombinase; C090472:SGS1 protein, S cerevisiae; D004265:DNA Helicases; D053484:RecQ Helicases; D004264:DNA Topoisomerases, Type I