Fig. 2

Activation of APC/C^CDC20 by phosphorylation. In the unphosphorylated APC/C, the C-box binding site on APC8 is occupied by an auto-inhibitory loop of APC1, thus preventing the C-box of CDC20 to bind to APC/C. Phosphorylation of a loop in APC3 subunits results in recruitment of CDK1-CyclinB-CKS complex to this loop, leading to phosphorylation of the APC1 loop and displacing it from the C-box binding site, and allowing the CDC20 C-box to associate with APC8. The IR tail of CDC20 interacts with APC3A while the phosphorylated loop of APC3B interacts with the IR tail of APC10. Coactivator binding induces the movement of the catalytic core in the ‘up’ position