BLM Helicase Ortholog Sgs1 Is a Central Regulator of Meiotic Recombination Intermediate Metabolism

SummaryThe BLM helicase has been shown to maintain genome stability by preventing accumulation of aberrant recombination intermediates. We show here that the Saccharomyces cerevisiae BLM ortholog, Sgs1, plays an integral role in normal meiotic recombination, beyond its documented activity limiting aberrant recombination intermediates. In wild-type meiosis, temporally and mechanistically distinct pathways produce crossover and noncrossover recombinants. Crossovers form late in meiosis I prophase, by polo kinase-triggered resolution of Holliday junction (HJ) intermediates. Noncrossovers form earlier, via processes that do not involve stable HJ intermediates. In contrast, sgs1 mutants abolish early noncrossover formation. Instead, both noncrossovers and crossovers form by late HJ intermediate resolution, using an alternate pathway requiring the overlapping activities of Mus81-Mms4, Yen1, and Slx1-Slx4, nucleases with minor roles in wild-type meiosis. We conclude that Sgs1 is a primary regulator of recombination pathway choice during meiosis and suggest a similar function in the mitotic cell cycle.

Graphical AbstractFigure optionsDownload high-quality image (168 K)Download as PowerPoint slideHighlights
► Sgs1 is required for normal noncrossover and crossover formation during meiosis
► Noncrossovers and crossovers form via different pathways in wild-type
► Noncrossovers and crossovers form via a common pathway in sgs1 mutants
► Polo kinase Cdc5 triggers joint molecule resolution in both wild-type and sgs1