The Bcl-2 (B-cell leukemia/lymphoma 2) family proteins function to either inhibit (Bcl-2 and Bcl-XL) or promote (Bax and Bad) apoptosis. Similar to other family member, Bad also exhibits sequence homology to Bcl-2. Bad can selectively dimerize with Bcl-xL and Bcl-2, but not with Bax, Bcl-xs, Mcl-1, or itself. In mammalian cells, Bad binds more strongly to Bcl-xL than Bcl-2. This may explain why Bad reverse the death repressor activity of Bcl-xL, but not that of Bcl-2