MULTIPLE GENE COPIES FOR BOMBYXIN, AN INSULIN-RELATED PEPTIDE OF THE SILKMOTH BOMBYX-MORI - STRUCTURAL SIGNS FOR GENE REARRANGEMENT AND DUPLICATION RESPONSIBLE FOR GENERATION OF MULTIPLE MOLECULAR-FORMS OF BOMBYXIN

Thirty-eight genes that encode bombyxin, the insulin-related brain sec retory peptide of the silkmoth Bombyx mori, have been cloned and chara cterized. These genes have been classified into four families, A, B, C and D, according to their sequence similarity. All the bombyxin genes lack introns. Five of them have structural features of pseudogenes. T he 38 genes cluster in the three DNA segments of Bombyx in unique dist ribution patterns. Their arrangement has been classified into three ca tegories: gene pairs, gene triplets and single genes. In the pairs, tw o bombyxin genes belonging to families B and A (B/A) or to families B and C (B/C) are apposed with opposite transcriptional orientation. All triplets are arranged in the order of the family-B, family-C and fami ly-A genes, and the transcriptional directions of the family-C and fam ily-A genes are opposite to the direction of the family-B gene. The bo mbyxin gene triplets may have been generated by an unequal crossing-ov er between two gene pairs, B/A and B/C. Crossing-over may have occurre d in the bombyxin family-B genes to increase their structural diversit y. Duplications may have served to multiply the bombyxin gene triplets . These genomic rearrangements are thought to have led to the generati on of multiple bombyxin gene copies and their diversity in structure a nd genomic organization. (C) 1996 Academic Press Limited