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 BAK1 for binding to MCL1 and can displace BAK1 from its binding site on MCL1 (By similarity). Competes with BIM/BCL2L11 for binding to MCL1 and can displace BIM/BCL2L11 from its binding site on MCL1. Interacts with MCL1 (PubMed:15694340, PubMed:17374615, PubMed:17389404). Interacts with BCL2A1 (Ref.11). Interacts with BAX (PubMed:15705586). Interacts with BCL2L10 (PubMed:23563182). Highly expressed in adult T-cell leukemia cell line. Up-regulated by p53/TP53, phorbol esters, double-stranded RNA, IFNB1/IFN-beta and viruses. The BH3 motif is essential for pro-apoptotic activity. Belongs to the PMAIP1 family.