Activation of the human anaphase-promoting complex by proteins of the CDC20/Fizzy family.

Abstract The initiation of anaphase and exit from mitosis depend on the activation of the cyclosome/anaphase-promoting complex (APC) that ubiquitinates regulatory proteins such as anaphase inhibitors and mitotic cyclins [1–4]. Genetic experiments have demonstrated that two related WD40-repeat proteins – called Cdc20p and Hct1p/Cdh1p in budding yeast and Fizzy and Fizzy-related in Drosophila – are essential for APC-dependent proteolysis [5–11]. Human orthologs of these proteins – hCDC20/p55 CDC [12] and hCDH1 – have recently been found to associate with APC in a cell-cycle-dependent manner [13,14]. Here, we show that the amount of hCDC20 and hCDH1 bound to APC correlates with a high ubiquitination activity of APC and that binding of recombinant hCDC20 and hCDH1 can activate APC in vitro . Our results suggest that the association between hCDH1 and APC is regulated by post-translational mechanisms, whereas the amount of hCDC20 bound to APC may in addition be controlled by hCDC20 synthesis and destruction [15]. The temporally distinct association of hCDC20 and hCDH1 with APC suggests that these proteins are, respectively, mitosis-specific and G1-specific activating subunits of APC.