Cloning of cDNAs for Cecropins A and B,and Expression of the Genes in the Silkworm,Bombyx mori

cDNA clones coding cecropins A and B were isolated from a cDNA library constructed from the fat body of immunized Bombyx mori larvae. The cloned cDNAs had an open reading frame of 63 amino acids, indicating the primary translated peptides were processed to form mature cecropins of 35 amino acid residues. The homology in the coding regions of cecropins A and B was 73%.

In immunized fat body, the expression of both cecropin A and B genes reached the maximal level 5 h after the injection of soluble peptidoglycan, and the high level was maintained until 9 h after immunization. The cecropin A and B genes were expressed at high levels in fat body and hemocytes, at lower but significant levels in malpighian tube, slightly in midgut, and none in silk gland.