BCL-2 homology (BH) domains within BCL-2 family members. (A) Schematic representation of BCL-2, BCL-X_L, BAK, and BAX and the relative positions of the BH1, BH2, BH3, and BH4 domains and transmembrane region. (B) Schematic overview of BAX open reading frame. Exons are numbered. BH1, BH2, and BH3 and transmembrane domains are shaded. Positions of PCR primers (A through D) are indicated. PCR amplification using primer pair A, B results in a 377-bp product. PCR amplification using primer pair C, D results in a 246-bp product.