Abstract: The heterotrimeric GTP-binding proteins are vital molecules in eukaryotic cell signal transduction;they mediate extracellular signals to pass down to the downstream effectors. In order to investigate the physiological function and action mechanism of the silkworm G protein which takes part in multiple signal transduction pathways, we found a known G protein alpha subunit homolog in silkworm genome database by means of bioinformatics. A novel G protein alpha subunit from Bombyx mori was cloned by PCR and RACE using specific primers and named BmGα73B. The full length BmGα73B gene (GenBank accession no. EU914850) was 1 509 bp with a 1 158 bp ORF coding for 385 amino acid residues. Sequence analysis aided by Blast and DNAstar revealed that the BmGα73B protein contained all the well conserved domains and motifs that were critical sites for interaction with receptors and other binding effectors compared with the already known Gα sequences in other species. RT-PCR was conducted to investigate the BmGα73B expression in different tissues and at different developmental stages. The results indicated that BmGα73B was widely expressed in B. mori tissues, especially rich in the midgut; it was also obviously present in head, Malpighian tubule and other tissues. The stage specific expression patterns indicated that BmGα73Bwas mainly expressed in larvae, also existed in early pupae, but less or not expressed in later pupae and adults. The results suggest that BmGα73B may play crucial roles at the early developmental stage of the B. mori midgut, which could be a clue to further investigate the function of G proteins in silkworm development.

Key words: G protein, alpha subunit, Bombyx mori, cloning, expression, RT-PCR