Sic1
Sic1, a protein, is a stoichiometric inhibitor of Cdk1-Clb (B-type cyclins) complexes in the budding yeast Saccharomyces cerevisiae. Because B-type cyclin-Cdk1 complexes are the drivers of S-phase initiation, Sic1 prevents premature S-phase entry. Multisite phosphorylation of Sic1 is thought to time Sic1 ubiquitination and destruction, and by extension, the timing of S-phase entry.
Read more about Sic1: Role of Sic1 in The Cell Cycle Control, Ubiquitin-dependent Degradation of Sic1, Multiple Phosphorylations Allow Fine-tuning, Sic1 Homologue in Human and Diseases, See Also