PDS1P, AN INHIBITOR OF ANAPHASE IN BUDDING YEAST, PLAYS A CRITICAL ROLE IN THE APC AND CHECKPOINT PATHWAY(S)

We report the isolation and characterization of pds1 mutants in Saccha romyces cerevisiae. The initial pds1-1 allele was identified by its in viability after transient exposure to microtubule inhibitors and its p recocious dissociation of sister chromatids in the presence of these m icrotubule inhibitors. These findings suggest that pds1 mutants might be defective in anaphase arrest that normally is imposed by a spindle- damage checkpoint. To further examine a role for Pds1p in anaphase arr est, we compared the cell cycle arrest of pds1 mutants and PDS1 cells after: (a) the inactivation of Cdc16p or Cdc23p, two proteins that are required for the degradation of mitotic cyclins and are putative comp onents of the yeast anaphase promoting complex (APC); (b) the inactiva tion of Cdc20p, another protein implicated in the degradation of mitot ic cyclins; and (c) the inactivation of Cdc13 protein or gamma irradia tion, two circumstances that induce a DNA-damage checkpoint. Under all these conditions, anaphase is inhibited in PDS1 cells but not in pds1 mutants. From these results we suggest that Pds1 protein is an anapha se inhibitor that plays a critical role in the control of anaphase by both APC and checkpoints. We also show that pds1 mutants exit mitosis and initiate new rounds of cell division after gamma irradiation and C dc13p inactivation but not after nocodazole-treatment or inactivation of Cdc16p, Cdc20p or Cdc23p function. Therefore, in the DNA-damage che ckpoint, Pds1p is required for the inhibition of cytokinesis and DNA r eplication as well as anaphase. The role of Pds1 protein in anaphase i nhibition and general cell cycle regulation is discussed.