Structure of two cecropin B-encoding genes and bacteria-inducible DNA-binding proteins which bind to the 5'-upstream regulatory region in the silkworm, Bombyx mori.

Two genomic DNAs encoding cecropin B (CecB), an antibacterial protein from Bombyx mori, were cloned and sequenced. The number of CecB genes was estimated to be more than four copies per haploid by genomic Southern blotting. Two genes, CecB1 and CecB2, were located tandemly within 12 kb in the same orientation. These two genes encoded identical amino acids, though 15 nucleotides (nt) were different in the coding region and the intron size varied. About 90% of the nt spanning 800 bp in the 5'-untranslated region (UTR) were identical between the two genes. This 5'-flanking region contained characteristic sequences such as a repetitive element of B. mori (Bm1), an interleukin-6 response element (IL-6 RE), and two putative lipopolysaccharide (LPS) response elements (LPS RE). An electrophoretic mobility shift assay (EMSA) showed that the fat body contains at least three different nuclear proteins inducible by bacteria which bind to the 5'-UTR, suggesting that these proteins may be involved in CecB expression triggered by bacteria.