CDC20 - Spindle Assembly Checkpoint

Spindle Assembly Checkpoint

Cdc20 is also a part of, and regulated by, the Spindle Assembly Checkpoint (SAC). This checkpoint ensures that anaphase proceeds only when the centromeres of all sister chromatids lined up on the metaphase plate are properly attached to microtubules. The checkpoint is held active by any unattached centromere; only when all centromeres are attached will anaphase commence. The APCCdc20 is an important target of the SAC, which consists of several different proteins, including Mad2, Mad3(BubR1), and Bub3. In fact, these three proteins, together with Cdc20, likely form the mitotic checkpoint complex (MCC), which inhibits APCCdc20 so that anaphase cannot begin prematurely. Moreover, Bub1 phosphorylates and thus inhibits Cdc20 directly, while in yeast Mad2 and Mad3, when bound to Cdc20, trigger its autoubiquitiniation. ( For more information see Spindle Checkpoint.)