Background: CDC20 is a WD repeat containing cell cycle-regulator that binds to and activates the ubiquitin-ligase activity of the APC/c (anaphase-promoting complex/cyclosome). APC/c ubiquitinating activity is responsible for the degradation of securin and cyclin B that prompts the onset of anaphase and exit from mitosis. CDC20 has also been reported to form a complex with histone deacetylases and can function as a transcriptional repressor involved in cell cycle arrest. As a regulator of APC/c activity, CDC20 plays a key role in the spindle-assembly checkpoint.