The execution of meiotic divisions in Saccharomyces cerevisiae is regulated by anaphase-promoting complex/cyclosome (APC/C)-mediated protein degradation. During meiosis, the APC/C is activated by association with Cdc20p or the meiosis-specific activator Ama1p. We present evidence that, as cells exit from meiosis II, APC/C(Ama1) mediates Cdc20p destruction. APC/C(Ama1) recognizes two degrons on Cdc20p, the destruction box and destruction degron, with either domain being sufficient to mediate Cdc20p destruction. Cdc20p does not need to associate with the APC/C to bind Ama1p or be destroyed. Coimmunoprecipitation analyses showed that the diverged amino-terminal region of Ama1p recognizes both Cdc20p and Clb1p, a previously identified substrate of APC/C(Ama1). Domain swap experiments revealed that the C-terminal WD region of Cdh1p, when fused to the N-terminal region of Ama1p, could direct most of Ama1p functions, although at a reduced level. In addition, this fusion protein cannot complement the spore wall defect in ama1Δ strains, indicating that substrate specificity is also derived from the WD repeat domain. These findings provide a mechanism to temporally down-regulate APC/C(Cdc20) activity as the cells complete meiosis II and form spores.
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