Cyclin-dependent kinase inhibitor 1 (p21) is an important intermediate by which p53/TP53 mediates its role as an inhibitor of cellular proliferation in response to DNA damage. P21 binds to and inhibits cyclin-dependent kinase activity,Porcinereventing phosphorylation of critical cyclin-dependent kinase substrates and blocking cell cycle progression. p21 functions in the nuclear localization and assembly of the cyclin D-CDK4 comple, Xenopus/Amphibian, and promotes its kinase activity towards RB1. At higher stoichiometric ratios,Porcine21 inhibits the kinase activity of the cyclin D-CDK4 comple, Xenopus/Amphibian,.