Fig. 5

Spindle assembly checkpoint (SAC) independent ubiquitination of Cyclin A2. a Phosphorylation of inactive, apo-APC/C leads to binding of CDK1-Cyclin A2-CKS1 complex to CDC20. The degrons of Cyclin A2 can bind in two different modes to APC/C^CDC20, only one mode is shown here that engages KEN- (K) and non-canonical D-box (D2), and activates ubiquitination of Cyclin A2. b Cyclin A can also bind to APC/C^CDC20-MCC complex. In the closed APC/C–MCC conformation, BUBR1 forms a lariat like structure between APC/C^CDC20 and CDC20^MCC via its multiple degrons. ABBA-box of Cyclin A2 (A) competes with the ABBA-box 2 of BUBR1 (A2) and can bridge both CDC20 molecules in APC/C by interaction of its D2- and KEN- boxes. This is proposed to induce the open conformation of APC/C–MCC and facilitates Cyclin A2 ubiquitination. For clarity, only relevant subunits are shown here. Yellow circle shows ubiquitination, degrons bounds with dashed lines indicate no interaction, those with solid lines indicate binding. Flexible linkers are shown by dashed lines. P denotes phosphorylation