p53 transcriptionally activates genes leading to cell cycle arrest or cell death (apoptosis). p21WAF1/CIP1 is a G1 cyclin/cyclin-dependent protein kinase inhibitor which blocks the activity of a G1 cyclin-dependent protein kinase. This results in cell cycle arrest. Transcription of the BAX gene is directly activated by p53-binding sites in the regulatory region of the gene. Bax is located in mitochondria. When overexpressed, Bax induces apoptosis.