 Cks1-dependent multi-phosphorylation occurs in a processive or semi-processive manner, evidenced by the lack of intermediate Sic1 phosphorylation states in normal cells.This processivity is also dependent on the presence of the cyclin docking site since increasing the numbers of mutations in this site decreases the net phosphorylation rate.Processive phosphorylation has two plausible mechanisms where a single binding event leads to the phosphorylation of two or more sites.