Bcl-2 family proteins. The domain arrangements of the known members of the Bcl-2 family are presented. The BH1, BH2, BH3, BH4, and transmembrane domains are indicated. In addition to human or murine proteins, included in the diagram are the chicken Nr13 protein, C. elegans proteins CED-9, EGL1, and CeBNIP, and the Drosophila proteins DBok (Drob1, dBorg 1, Debcl). Homologues from viruses, xenopas, and marine sponges are not depicted. Human noxa (APR) has only one BH3 domain.