Isolation and Characterization of a Silkworm cDNA Encoding a Protein Homologous to the 14kDa Protein of Bovine Ubiquinol-cytochrome C Reductase

In this study, we characterized the small subunit of ubiquinol-cytochrome C reductase (Bmuccr) of the silkworm Bombyx mori, a model insect of Lepidopteron species. The Bmuccr gene covers a 1.4 kb genome region and contains 3 exons. The ORF contained 354bp and encoded 117 amino acid residues, which shares 69% overall amino acid sequence identities with the subunit VII of ubiquinol-cytochrome C reductase from bovine. Phylogenetic tree showed Bmuccr had high homology with T. castaneum homologous. The multiple sequence alignment of 16 subunit VII homologues shows that Bmuccr is very hydrophilic, has a characteristic charge distribution, and has a high helical content. Expression analysis indicated that Bmuccr was highly expressed in larva stage and was down-regulated in embryos stage and adult stage of silkworm. The tissue-specific expression indicated Bmuccr had high-expression level in tissues that consume oxygen. The analysis of domain structure of this protein suggested that it might be involved in correct assembly of the cytochrome bcl complex. Definition of the homologous of bovine subunit VII of ubiquinol-cytochrome C reductase should facilitate further analysis of structure/function relationships of silkworm cytochrome bcl complex.