Bcl-B, a novel Bcl-2 family member that differentially binds and regulatesBax and Bak

A novel human member of the Bcl-2 family was identified, Bcl-B, which is cl osest in amino acid sequence homology to the Boo (Diva) protein. The Bcl-B protein contains four Bcl-2 homology (BH) domains (BH1, BH2, BH3, BH4) and a predicted carboxyl-terminal transmembrane (TM) domain. The BCL-B mRNA is widely expressed in adult human tissues. The Bcl-B protein binds Bcl-2, Bcl -X-L, and Bar but not Bah. In transient transfection assays, Bcl-B suppress es apoptosis induced by Bar but not Bah. Deletion of the TM domain of Bcl-B impairs its association with intracellular organelles and diminishes its a nti-apoptotic function. Bcl-B thus displays a unique pattern of selectivity for binding and regulating the function of other members of the Bcl-2 fami ly.