Figure 2.

Regulation of the G2/M transition and mitotic exit by the APC/C. Destruction of Pds1 (securin) by APC/C^Cdc20 triggers the metaphase-anaphase transition. Checkpoint pathways monitoring spindle attachment or DNA damage can inhibit APC/C^Cdc20 activity by direct association of spindle assembly checkpoint (SAC) components or phosphorylation by PKA. The exit from mitosis initially requires the degradation of several regulatory proteins including the B-type cyclin Clb2 by APC/C^Cdc20. Final mitotic exit requires APC/C^Cdh1 which continues Clb2 degradation to completion. APC/C^Cdh1 remains active in G1 partially destroying Cdc20. The decision to enter meiosis occurs early in G1 and requires APC/C^Cdc20 destruction of Ume6. Inhibition of Cdc20 function by PKA phosphorylation drives the cell through G1 to reinitiate another round of mitotic cell division.