Plays a role in apoptosis. Diffusely distributed throughout the cytosol. Predominantly localized to cytosolic organelles. Isoform 1 is widely expressed. Isoform 2 is testis-specific. Phosphorylated by MELK, leading to inhibit its pro-apoptotic function. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the Bcl-2 family.