A Bombyx mori gene, BmChi-h, encodes a protein homologous to bacterial and baculovirus chitinases

Abstract

We have cloned and characterized a novel chitinase gene ( BmChi-h) from the silkworm, Bombyx mori. BmChi-h cDNA has an open reading frame of 1665 nucleotides, encoding a protein of 555 amino acid residues. The predicted protein shared extensive similarities with bacterial and baculovirus chitinases in both amino acid sequences (73% identity with Serratia marcescens chiA and 63% with Autographa californica nucleopolyhedrovirus chiA) and domain architectures. BmChi-h was a single-copy gene and located on chromosome 7. The expression of BmChi-h mRNA was observed in a stage- and tissue-specific manner that was almost identical to that of another chitinase gene previously cloned from B. mori. We further determined the overall genomic organization of BmChi-h. There was no intron in the ORF of BmChi-h. However, BmChi-h was transcribed from three promoters, which generated three isoforms in the 5′-UTR of the transcript. Phylogenetic analysis suggested that ancestral species of B. mori acquired the chitinase gene from a bacterium or an ancestral baculovirus via horizontal gene transfer.