The Ama1-directed APC/C ubiquitin ligase regulates the Smk1 MAPK during meiosis in yeast

Smk1 is a meiosis-specific MAPK homolog in Saccharomyces cerevisiae that regulates the post-meiotic program of spore formation. Similar to other MAPKs, it is activated via phosphorylation of the T-X-Y motif in its regulatory loop, but the signals controlling Smk1 activation have not been defined. Here we show that Ama1, a meiosis-specific activator of the anaphase-promoting complex/cyclosome (APC/C) promotes Smk1 activation during meiosis. A weakened allele of CDC28 suppresses the sporulation defect of an ama1 null strain and increases the activation state of Smk1. The function of Ama1 in regulating Smk1 is independent of the FEAR/MEN network, which promotes exit from mitosis and exit from meiosis I through the Cdc14 phosphatase. The data indicate that Cdc28 and Ama1 function in a pathway to trigger Smk1-dependent steps in spore morphogenesis. We propose that this novel mechanism for controlling MAPK activation plays a role in coupling the completion of meiosis II to gamete formation.

Key Words: AMA1, CDC28, SMK1, meiosis, sporulation

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