Promotes activation of caspases and apoptosis. Promotes mitochondrial membrane changes and efflux of apoptogenic proteins from the mitochondria. Contributes to p53/TP53-dependent apoptosis after radiation exposure. Promotes proteasomal degradation of MCL1. Competes with BIM/BCL2L11 for binding to MCL1 and can displace BIM/BCL2L11 from its binding site on MCL1 (By similarity). Competes with BAK1 for binding to MCL1 and can displace BAK1 from its binding site on MCL1. Interacts with MCL1 (PubMed:10807576, PubMed:15901672, PubMed:15694340, PubMed:17389404). Interacts with BCL2A1 (By similarity). Interacts with BAX (By similarity). Interacts with BCL2L10 (By similarity). Detected in thymocytes after irradiation with X-rays. Not detectable in untreated thymocytes (at protein level). Detected in embryonic neural precursor cells of the telencephalon Constitutively expressed at low levels in adult brain, testis, thymus, spleen, lung and kidney. Up-regulated after exposure to ionizing radiation and other genotoxic agents. Up-regulation is mediated by p53. The BH3 motif is essential for pro-apoptotic activity. Belongs to the PMAIP1 family.