In vitro processing of the dsrnase precursor isolated from silkworm midgut tissue, Bombyx mori

Analysis of cDNA encoding the double-stranded ribonuclease (Bm-dsRNase) of the silkworm, Bombyx mori, elucidated a possible conclusion that the 41 kDa mature dsRNase is produced from the 45 kDa precursor protein in the middle midgut tissue by post-translational processing. To strengthen this speculation, the 41 kDa protein was produced in vitro: the 43 kDa-45 kDa protein-rich fraction was partially purified by gel filtration and then treated with bovine trypsin. Specifc conversion of the 43 kDa and 45 kDa proteins into the enzymically-active 41 kDa protein was demonstrated by a Western blot analysis and dsRNase activity assay, strongly supporting that the 41 kDa Bm-dsRNase is produced in vivo by the limited proteolysis that was induced by an endogenous trypsin-like enzyme, and immediately released into midgut lumen.