Fig. (1).

ATM and its target proteins. In the active state ATM phosphorylates target proteins that signal to cell cycle checkpoints, DNA repair proteins or to the cell death machinery. Phosphorylation of Brca1 or the activation of the MRN complex results in the initiation of DNA repair. Activation of cell cycle checkpoints that lead to cell cycle arrest are achieved by phosphorylation of the p53 tumor suppressor protein or the Chk2 kinase. In addition, by transcriptional induction of pro-apoptotic proteins like Bax and PUMA, p53 can also induce apoptosis.