Disjunction of homologous chromosomes in meiosis I depends on proteolytic cleavage of the meiotic cohesin Rec8 by separin

It has been proposed but never proven that cohesion between sister chromati ds distal to chiasmata is responsible for holding homologous chromosomes to gether while spindles attempt to pull them toward opposite poles during met aphase of meiosis I. Meanwhile, the mechanism by which disjunction of homol ogs is triggered at the onset of anaphase I has remained a complete mystery . In yeast, cohesion between sister chromatid arms during meiosis depends o n a meiosis-specific cohesin subunit called Rec8, whose mitotic equivalent, Scc1, is cleaved at the metaphase to anaphase transition by an endopeptida se called separin. We show here that cleavage of Rec8 by separin at one of two different sites is necessary for the resolution of chiasmata and the di sjunction of homologous chromosomes during meiosis.