Cloning and Sequencing of cDNA Encoding the Diazepam Binding Inhibitor (DBI)

The anti-morphine peptide PPC from dog brain has an inhibitory effect on morphine analgesia. It is highly homologous to DBI. The analgesic effect of bovine DBI was measured, showing the potentiation effect on morphine analgesia. In order to study the relationship between PPC and DBI, cDNA library derived from dog liver had been screened using partial gene of rat DBI as a probe. A positive clone was obtained. The entire sequence of the insert of this positive clone provided complete sequence of a peptide which was identified as the DBI peptide. It shows 88.5% homology with pig DBI, 87.4% with bovine, 83.9% with human, 46.5% with yeast, respectively. The sequence of N-terminal 50 amino acid residues except 55th, 58th site and C-terminal 17 amino acids is the same to DBI from dog. PPC has 23 amino acids more than DBI inside.