The cell division cycle protein 20 homolog is an essential regulator of cell division that is encoded by the CDC20 gene in humans. To the best of current knowledge its most important function is to activate the anaphase promoting complex , a large 11-13 subunit complex that initiates chromatid separation and entrance into anaphase. The APC/CCdc20 protein complex has two main downstream targets. Firstly, it targets securin for destruction, enabling the eventual destruction of cohesin and thus sister chromatid separation. It also targets S and M-phase cyclins for destruction, which inactivates S/M cyclin-dependent kinases and allows the cell to exit from mitosis. A closely related protein, Cdc20homologue-1 plays a complementary role in the cell cycle.