A DIAZEPAM-BINDING INHIBITOR (DBI) HOMOLOG FROM THE TOBACCO HORNWORM, MANDUCA-SEXTA

A cDNA clone encoding a protein with 42-51% identity to the mammalian diazepam binding inhibitors (DBIs) has been isolated and sequenced from a midgut cDNA library of the tobacco hornworm, Manduca sexta. The putative M. sexta DBI is 90 residues in length and shares the predicted internal a-helices common to the mammalian DBIs. Sequence alignments indicate that the M. sexta DBI contains three potential proteolytic cleavage site lysines in the same positions as the mammalian DBIs. High DBI mRNA levels were found in larval midgut, larval fat body, and adult ovary. DBI mRNA was also detected in larval prothoracic glands, larval nerve cord, and adult testis. These results suggest that the putative M. sexta DBI is an important gene product with a high degree of identity to the known mammalian DBIs. The M. sexta DBI may therefore be the functional homolog to the mammalian DBIs.