Cyclins are a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes.

Cyclin is degraded by the ubiquitin pathway.
Inhibitors of mammalian G1 cyclin
Cyclins and cancer II: Cyclin D and CDK inhibitors come of age
p21 is a universal inhibitor of cyclin kinases
Inhibitors of mammalian G1 cyclin-dependent kinases.
Deletions of the cyclin-dependent kinase-4 inhibitor gene in multiple human cancers
Beta-catenin regulates expression of cyclin D1 in colon carcinoma cells
Cloning of p27Kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals
The p21 Cdk-interacting protein Cip1 is a potent inhibitor of G1 cyclin-dependent kinases.
A new regulatory motif in cell-cycle control causing specific inhibition of cyclin D/CDK4.