BNIP3, formerly NIP3 (nineteen kDa interacting protein-3), is a pro-apoptotic, mitochondrial protein classified in the Bcl 2 family based on limited sequence homology to the Bcl 2 homology 3 (BH3) domain (amino acids 110-118) and C-terminal TM domain. BNIP3 expressed in yeast and mammalian cells interacts with survival promoting proteins Bcl 2, Bcl XL, CED9 and the adenovirus E1B 19K protein. BNIP3 represents a subfamily of Bcl 2 related proteins, which functions without a typical BH3 domain to regulate apoptosis from both mitochondrial and nonmitochondrial sites by selective Bcl 2/Bcl XL interactions.