Spindle Assembly Checkpoint Overview
The spindle assembly checkpoint (SAC) is an active signal produced by improperly attached kinetochores, which is conserved in all eukaryotes. The SAC stops the cell cycle by negatively regulating CDC20, thereby preventing the activation of the polyubiquitylation activities of anaphase promoting complex (APC). The proteins responsible for the SAC signal compose the mitotic checkpoint complex (MCC), which includes SAC proteins, MAD2/MAD3 (mitotic arrest deficient), BUB3 (budding uninhibited by benzimidazole), and CDC20. Other proteins involved in the SAC include MAD1, BUB1, MPS1, and Aurora B. For higher eukaryotes, additional regulators of the SAC include constituents of the ROD-ZW10 complex, p31comet, MAPK, CDK1-cyclin-B, NEK2, and PLK1.
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