Figure 8. Model for SCF-mediated regulation of COMA assembly at the budding yeast kinetochore.

(A) Scheme illustrating stepwise phosphorylation of the degron motif on Ame1 by Cdk1 and protection from phosphorylation within the kinetochore. In addition to Cdk1, other kinases might be involved in addition, in particular in the phosphorylation of Okp1. (B) Cell cycle regulation of COMA complex stability; for details, see discussion. In S-phase, COMA is only partially phosphorylated, allowing assembly at the kinetochore. In M-phase, free COMA is fully phosphorylated and targeted for degradation, while kinetochore-bound COMA is protected.