APC is also an acronym for the anaphase promoting complex. The APC is an E3 ubiquitin ligase that plays a key roll in control of the cell cycle. Ubiquitin ligases promote regulated proteolysis (protein degradation) by attaching chains of a small protein called ubiquitin to target proteins, which causes their degradation. The APC has two major mitotic substrate specificity factors that target different proteins for degradation at different times in the cell cycle. These are known as Cdc20 and Cdh1.

The APC has two major functions:
1) To promote the onset of anaphase by allowing chromosomes to separate.
2) To establish and maintain a low level of Cyclin-CDK activity during G1 phase of the cell cycle.

Function 1
The APC targets a protein known as securin for degradation. Securin is an inhibitor of the protease called separase that cleaves a protein called cohesisn, which holds sister chromatids together. Thus when securin is present seperase is not active and sister chromatids are held together. However, when securin is targeted for degradation by the APC, seperase becomes active and sister chromatids are separated (anaphase occurs). This is carried out by the specificity factor Cdc20.

Function 2
The cell cycle is built upon the principle of an oscillator. The key component of this oscillator is the Cyclin Dependent Kinase or CDK. Levels of CDK are low in G1 and peak in mitosis. The APC promotes the mitosis to G1 transition of the cell cycle by targeting cyclins, the CDK activators, for degradation beginning in anaphase and persisting throughout G1. The low CDK level established in late anaphase allows the cells to exit from mitosis, and the maintenance of this low level of activity during G1 prevents DNA replication from happening prematurely. This is mediated by the specificty factors Cdc20 and Cdh1 in late mitosis, and by Cdh1 in G1.