Bovine and Human cDNA Sequences Encoding a Putative Benzodiazepine Receptor Ligand

Abstract

CDNAs containing the entire coding sequence of endozepine, a putative ligand of the benzodiazepine receptor, were isolated from bovine and human cDNA libraries. These libraries were constructed using a novel oligonucleotide adapter molecule that allowed us to combine the use of G/C tailing with the preservation of the unique Eco RI site in the vector, .lambda.gt10. The amino acid sequences derived from these cDNA clones are identical to those previously determined for the purified proteins and are homologous to a related rat protein termed diazepam-binding inhibitor. The endozepine proteins are highly conserved, as illustrated by the finding that the nucleotide sequences of the coding regions are 93% conserved between the bovine and human forms. Analysis of these sequences indicates that endozepine is not, as expected, derived from a precursor molecule containing a transient signal peptide. Moreover, Northern analyses using the cloned cDNAs as hybridization probes indicate that the 650-nucleotide endozepine mRNA is expressed in a number of peripheral tissues in addition to brain. These observations may be consistent with a recent report describing the presence in peripheral tissues of benzodiazepine receptors on the outer mitochondrial membrane (Anholt et al., 1986). In addition to the endozepine cDNAs, we also isolated a bovine cDNA clone which encodes a larger protein, a portion of which is homologous to endozepine. This related protein may be synthesized in a precursor form containing putative signal peptide and membrane-spanning domains.