ATM/p53 regulation network inTP53-mutant,ATM-mutant, and wild-type tumors based on their differential global expression profiles. Regulation of IR-induced transcriptional responses by ATM and p53. All transcriptional responses to IR are under ATM control, whereby a subset of responses involves p53 and either supports apoptosis (cluster 1) or inhibits IR-induced survival (cluster 3). Responses independent of p53 support damage-induced survival (cluster 2). A small subset of genes involved in DNA repair and transcription regulation is suppressed by ATM after IR (cluster 4).