Suppressor of apoptosis. Modulates unfolded protein response signaling. Modulates ER calcium homeostasis by acting as a calcium-leak channel. Negatively regulates autophagy and autophagosome formation, especially during periods of nutrient deprivation, and reduces cell survival during starvation. Interacts with BCL2. Interacts with BCL2L1. Highly abundant in adult testis. During spermatogenesis, it is mainly expressed postmeiotically. 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.