The anaphase promoting complex targeting subunit ama1 links meiotic exit to cytokinesis during sporulation in Saccharomyces cerevisiae

Ascospore formation in yeast is accomplished through a cell division in which daughter nuclei are engulfed by newly formed plasma membranes, termed prospore membranes. Closure of the prospore membrane must be coordinated with the end of meiosis II to ensure proper cell division. AMA1 encodes a meiosis-specific activator of the anaphase promoting complex (APC). The activity of APC ^Ama1 is inhibited before meiosis II, but the substrates specifically targeted for degradation by Ama1 at the end of meiosis are unknown. We show here that ama1δ mutants are defective in prospore membrane closure. Ssp1, a protein found at the leading edge of the prospore membrane, is stabilized in amalδ mutants. Inactivation of a conditional form of Sspl can partially rescue the sporulation defect of the amalA mutant, indicating that an essential function of Amal is to lead to the removal of Ssp1. Depletion of Cdc15 causes a defect in meiotic exit. We find that prospore membrane closure is also defective in Cdcl5 and that this defect can be overcome by expression of a form of Amal in which multiple consensus cyclin-dependent kinase phosphorylation sites have been mutated. These results demonstrate that APC ^Amal functions to coordinate the exit from meiosis II with cytokinesis.