Essential mediator of p53/TP53-dependent and p53/TP53- independent apoptosis. Interacts with MCL1 and BCL2A1. Interacts with BCL2 and BCL2L1/BCL-XL. By DNA damage, glucocorticoid treatment, growth factor deprivation and p53/TP53. Ubiquitously expressed. Belongs to the Bcl-2 family. 4 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.