Expression of reovirus type 3 (Dearing) sigma 1 and sigma s polypeptides in Escherichia coli

The reovirus S1 gene codes for two polypeptides: sigma 1 and sigma s. In order to characterize the structure and function of the sigma 1 polypeptide, we have expressed the sigma 1 protein in Escherichia coli. The S1 gene from mammalian reovirus type 3 (Dearing strain) and the variant K strain were subcloned into an expression vector containing the tac (trp-lac) promoter designed to express foreign gene products in E. coli efficiently. The hybrid plasmids, upon induction with isopropyl-beta-D-thiogalactopyranoside, expressed two polypeptides that were detected by [35S]methionine labelling. One of the induced proteins had a relative molecular mass (Mr) of approx. 46,000 and corresponded to sigma 1, as shown by immunoprecipitation with goat anti-reovirus antibody and a monoclonal antibody against sigma 1. The second induced protein had a Mr of approx. 12,000 and was very similar to sigma s as judged by comparative tryptic peptide map analysis. Protein sigma 1 produced in E. coli was shown to be functional as judged from its ability to bind to mouse L fibroblasts.