The Bcl-2 (B-cell leukemia/lymphoma 2) family proteins function to either inhibit (Bcl-2 and Bcl-XL) or promote (Bax and Bak) apoptosis. Bax contains the conserved Bcl-2 homology 1 (BH1) and 2 (BH2) domains that allow for its homodimerization or heterodimerization with Bcl-2. When Bcl-2 is in excess, apoptosis is inhibited. However, if Bax levels increase in response to a death signal, the cell is pushed toward death.