 Following this, the T33, T45, and S76 residues are phosphorylated by Cln2-Cdk1, but no degron pairs are phosphorylated.However, these phosphorylated sites enhance Clb5-Cdk1 docking, leading to increased Sic1 phosphorylation at suboptimal sites and a positive feedback loop where Clb5-Cdk1 inhibition is continually decreased while Sic1 degradation is increased.The protein p27Kip1 is a human homologue of Sic1, both having a conserved inhibitory domain, but p27Kip1 inhibits G1 cyclins and not cyclin B.