Bax-α is thought to form heterodimers with Bcl-2 and prevent apoptotic cell death. A sequence was isolated from oligodendrocyte cDNA corresponding to the uncloned 3 end of the rat bax-α coding region and part of the 3 UTR via a degenerate polymerase chain reaction (PCR)-based cloning method. The rat bax-α clone is 96 and 91% homologous to mouse and human clones, respectively, and the 3 UTR demonstrates high homology with the cloned human 3 UTR. Northern analysis demonstrated that the 1.0 kb bax-α mRNA species was predominant. bax-α mRNA is expressed in mitotic, oligodendrocyte progenitors, and is subsequently down-regulated 2-fold in differentiating oligodendrocytes.