This gene encodes a potent cyclin-dependent kinase inhibitor. The encoded protein binds to and inhibits the activity of cyclin-CDK2 or -CDK4 complexes, and thus functions as a regulator of cell cycle progression at G1. The expression of this gene is tightly controlled by the tumor suppressor protein p53, through which this protein mediates the p53-dependent cell cycle G1 phase arrest in response to a variety of stress stimuli. This protein can interact with proliferating cell nuclear antigen (PCNA), a DNA polymerase accessory factor, and plays a regulatory role in S phase DNA replication and DNA damage repair. This protein was reported to be specifically cleaved by CASP3-like caspases, which thus leads to a dramatic activation of CDK2, and may be instrumental in the execution of apoptosis following caspase activation. Multiple alternatively spliced variants have been found for this gene. Alias Symbols: CAP20, CDKN1, CIP1, MDA-6, P21, SDI1, WAF1, p21CIP1 Protein Interaction Partner: CCND1, PCNA, KRT31, TRIM54, TEX11, IKZF3, UBC, TRAF1, TCF4, SKP2, CCND3, CCND2, PHKG2, PHKA1, NCL, HSPA9, HSPA8, HSPA5, HSPA2, HSPA1A, HNRNPA2B1, CDK2, CDK5, CDK4, CDK3, CDC20, CCNE1, CCNB1, CCNA2, CAMK2D, ABR, GIGYF2, ANKRD17, UBR4, SNRNP200, FBXO21, PUF Protein Size: 164