AN ESP1 PDS1 COMPLEX REGULATES LOSS OF SISTER-CHROMATID COHESION AT THE METAPHASE TO ANAPHASE TRANSITION IN YEAST/

Cohesion between sister chromatids during G2 and M phases depends on t he ''cohesin'' protein Scc1p (Mcd1p). Loss of cohesion at the metaphas e to anaphase transition is accompanied by Scc1p's dissociation from c hromatids, which depends on proteolysis of Pds1p mediated by a ubiquit in protein ligase called the anaphase promoting complex (APC). We show that destruction of Pds1p is the APC's sole role in triggering Scc1p' s dissociation from chromatids and that Pds1p forms a stable complex w ith a 180 kDa protein called Esp1p, which is essential for the dissoci ation of Scc1p from sister chromatids and for their separation. We pro pose that the APC promotes sister separation not by destroying cohesin s but instead by liberating the ''sister-separating'' Esp1 protein fro m its inhibitor Pds1p.