Structure and organization of four clustered genes that encode bombyxin, an insulin-related brain secretory peptide of the silkmoth Bombyx mori.

Four genes encoding bombyxin have been located in a 14-kilobase Bombyx genomic DNA segment. All of these genes encode preprobombyxin, the precursor molecule for bombyxin, with the domain organization of signal peptide/B chain/C peptide/A chain. Bombyxins are classified as family A or B according to their sequence homology. Two genes, each belonging to a different family, are closely apposed to form a pair with opposite orientation, presumably forming a regulatory unit for transcription. Genomic Southern blot hybridization suggested that there are many such gene pairs in the Bombyx genome. Differences between bombyxin genes and vertebrate insulin-family genes indicate that different mechanisms operate in the evolution of invertebrate and vertebrate insulin-family genes.