Cdc20 and cdh1 are coactivators of the anaphase-promoting complex (APC). APCcdc20 is necessary for the metaphase-anaphase transition and, at the end of mitosis, vertebrate cdc20 itself becomes a target for degradation through KEN-box-dependent APCcdh1 activity. By studying the degradation of fluorescent protein chimaeras in mammalian oocytes and early embryos, we found that cdc20 was degraded through two independent degradation signals (degrons), the KEN box and a newly described CRY box. In both oocytes and G1-stage embryos, the rate of degradation through the CRY box was greater than through the KEN box, although both were mediated by APCcdh1. Thus, mammalian oocytes and embryos have the capacity to recognize two degrons in cdc20.
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