 Apart from being an often-overlooked component of the Cdk1 cyclin complex, Cks1 is critical for Sic1 multi-phosphorylation and degradation.The phospho-binding pocket of Cks1 is capable of binding independently to phosphorylated CDK sites on Sic1.Additionally, the binding affinity of Cks1 for phosphoserines is extremely weak, essentially making Cks1 binding dependent on the presence of phosphothreonines only.