In the presence of an appropriate stimulus, accelerates programmed cell death by binding to, and antagonizing the anti-apoptotic action of BCL2. Homodimer. Formation of the homodimer is zinc-dependent. Forms heterodimers with BCL2 and BCL2L1 isoform Bcl-X(L). Forms heterooligomers with BAX (By similarity). Interacts with BCL2A1 (PubMed:18462686). Interacts withRTL10/BOP (PubMed:18462686). Interacts with VDAC1 (By similarity). Interacts with GIMAP3/IAN4 and GIMAP5/IAN5 (PubMed:16509771). (Microbial infection) Interacts with gamma-herpesvirus 68 protein vBCL2. Widely expressed. Intact BH3 motif is required by BIK, BID, BAK, BAD and BAX for their pro-apoptotic activity and for their interaction with anti-apoptotic members of the Bcl-2 family. Belongs to the Bcl-2 family.