Accelerates programmed cell death by binding to, and antagonizing the apoptosis repressor BCL2 or its adenovirus homolog E1B 19k protein. Under stress conditions, undergoes a conformation change that causes translocation to the mitochondrion membrane, leading to the release of cytochrome c that then triggers apoptosis. Promotes activation of CASP3, and thereby apoptosis. Homodimer. Forms higher oligomers under stress conditions. Forms heterooligomers with BAK. Interacts with BCL2L11. Interaction with BCL2L11 promotes BAX oligomerization and association with mitochondrial membranes, with subsequent release of cytochrome c. Forms heterodimers with BCL2, E1B 19K protein, BCL2L1 isoform Bcl-X(L), BCL2L2, MCL1 and A1. Interacts with SH3GLB1. Interacts with SFN and YWHAZ; the interaction occurs in the cytoplasm. Under stress conditions, JNK-mediated phosphorylation of SFN and YWHAZ, releases BAX to mitochondria. Interacts with RNF144B, which regulates the ubiquitin-dependent stability of BAX. Interacts with CLU under stress conditions that cause a conformation change leading to BAX oligomerization and association with mitochondria. Does not interact with CLU in unstressed cells (By similarity). Interacts with FAIM2/LFG2 (By similarity). Interacts with BOP (By similarity). Interacts (via a C-terminal 33 residues) with NOL3 (via CARD domain); inhibits BAX activation and translocationand consequently cytochrome c release from mitochondria (PubMed:15383280). Interacts with GIMAP3/IAN4 and GIMAP5/IAN5; this interaction is increased, when cells initiate apoptosis upon IL2 withdrawal (By similarity). Interacts with IRF3; the interaction is direct and, upon virus infection, mediates the formation of the apoptosis complex TOMM70:HSP90AA1:IRF3:BAX (By similarity). Interacts with MOAP1, facilitating BAX-dependent mitochondrial outer membrane permeabilization and apoptosis (By similarity). Interacts with BCL2L10/BCL-B (By similarity). Colocalizes with 14-3-3 proteins in the cytoplasm. Under stress conditions, undergoes a conformation change that causes release from JNK-phosphorylated 14-3-3 proteins and translocation to the mitochondrion membrane (By similarity). Expressed in a wide variety of tissues, with highest levels in the testis and ovary. 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.