Sister chromatid separation and chromosome re-duplication are regulated by different mechanisms in response to spindle damage

Abstract

In yeast, anaphase entry depends on Pds1 proteolysis, while chromosome re-duplication in the subsequent S-phase involves degradation of mitotic cyclins such as Clb2. Sequential proteolysis of Pds1 and mitotic cyclins is mediated by the anaphase-promoting complex (APC). Lagging chromosomes or spindle damage are detected by surveillance mechanisms (checkpoints) which block anaphase onset, cytokinesis and DNA re-replication. Until now the MAD and BUB genes implicated in this regulation were thought to function in a single pathway that blocks APC activity. We show that spindle damage blocks sister chromatid separation solely by inhibiting APC(Cdc20)-dependent Pds1 proteolysis and that this process requires Mad2. Blocking APC(Cdh1)-mediated Clb2 proteolysis and chromosome re-duplication does not require Mad2 but a different protein, Bub2. Our data imply that Mad1, Mad2, Mad3 and Bub1 regulate ApC(Cdc20), whereas Bub2 regulates ApC(Cdh1).