cDNA cloning and gene expression of cecropin D, an antibacterial protein in the silkworm, Bombyx mori

We have isolated a cDNA clone encoding a cecropin D precursor from the fat body of Bombyx mori larvae immunized with bacteria by means of differential display. The cDNA contains 298 bp with a coding region of 183 bp for 61 am ino acids plus a termination codon (TAG), a 5'-untranslated region of 36 bp , and a 3'-untranslated region of 79 bp including the poly(A) tail. There i s a polyadenylation signal sequence of AATAAA at position 266, 43 nucleotid es downstream from the termination codon TAG. The homology of the deduced a mino acids is greater to the cecropin D precursor from Hyalophora cecropia (67% identity) than to the precursors of cecropins A and B from B. mori (49 % to both). Northern blotting analyses reveal that the gene expression of c ecropin D is detectable by 4 h after the bacterial injection and reaches th e maximal level at 24 h. That high level is maintained up to 48 h post-immu nization. Additionally, the gene is expressed mainly in the fat body and sl ightly in hemocytes, but it is undetectable in other tissues such as the mi dgut, the Malpighian tubule and silk gland. (C) 1999 Elsevier Science Inc. All rights reserved.