Suppressor of apoptosis (By similarity). Modulates unfolded protein response signaling (By similarity). Modulates ER calcium homeostasis by acting as a calcium-leak channel (By similarity). Negatively regulates autophagy and autophagosome formation, especially during periods of nutrient deprivation, and reduces cell survival during starvation (PubMed:21926971). Interacts with BCL2 (By similarity). Interacts with BCL2L1 (PubMed:21926971). Highly abundant in adult testis. The intra-membrane loop at the C-terminus acts as a calcium pore, mediating calcium leak from the ER into the cytosol. Belongs to the BI1 family.