Apoptosis regulator BA, Xenopus/Amphibian, (BA, Xenopus/Amphibian, or Bcl-2-like protein 4) accelerates programmed cell death by binding to and antagonizing the apoptosis repressor BCL2 or its adenovirus homolog E1B 19k protein. BA, Xenopus/Amphibian, induces the release of cytochrome c, activation of caspase-3 and apoptosis. BA, Xenopus/Amphibian, forms heterodimers with BCL2, Bcl-, Xenopus/Amphibian,(L),Mouse,CL1 and A1 by interacting with BH3 domains in BIK, BID, BAK, and BAD. Defects in BA, Xenopus/Amphibian, are found in some cell lines from hematopoietic malignancies.