P21

Cyclin-dependent kinase inhibitor 1A (p21, Cip1), also known as CDKN1A, is a human gene.

p21, also known as cyclin-dependent kinase inhibitor 1A or CDKN1A, is a human gene on chromosome 6 (location 6p21.2), that encodes a cyclin-dependent kinase inhibitor that directly inhibits the activity of cyclin-CDK2 and cyclin-CDK4 complexes. p21 functions as a regulator of cell cycle progression at G1 phase. The expression of p21 is controlled by the tumor suppressor protein p53.

The function of this gene relates in part to stress response.

p21 is also mediating the resistance of hematopoietic cells to an infection with HIV by complexing with the HIV integrase and thereby aborting chromosomal integration of the provirus.