Nora, a BH3-only member of the Bcl-2 family and candidate mediator of p53-induced apoptosis

A critical function of tumor suppressor p53 is the induction of apoptosis i n cells exposed to noxious stresses. We report a previously unidentified pr o-apoptotic gene, Nora. Expression of Nora induction in primary mouse cells exposed to x-ray irradiation was dependent on p53, Nora encodes a Bcl-2 ho mology 3 (BH3)-only member of the Bcl-2 family of proteins; this member con tains the BH3 region but not other BH domains. When ectopically expressed, Nora underwent BH3 motif-dependent Localization to mitochondria and interac ted with anti-apoptotic Bcl-2 family members, resulting in the activation o f caspase-9. We also demonstrate that blocking the endogenous Nora inductio n results in the suppression of apoptosis. Nora may thus represent a mediat or of p53-dependent apoptosis.