Fig. 1

ATM (ataxia telangiectasia mutated) and ataxia-telangiectasia-mutated-and-Rad3-related kinase (ATR) protein kinases phosphorylate p53 at serine 15 to activate and enhance the p53 stability. The phosphorylation of a variety of substrates, including casein kinase (CK1), checkpoint kinase 1 (Chk2), and p53, regulates cancer cell viability by modulating many critical biochemical pathways that lead to cell cycle arrest, DNA repair, senescence, and death