Expression and glycosylation of the respiratory syncytial virus G protein in Saccharomyces cerevisiae.

A cDNA encoding the entire amino acid sequence of the G glycoprotein of respiratory syncytial virus (RSV) was inserted into a yeast-Escherichia coli shuttle vector such that expression of the virus gene was regulated by the yeast GAL1 promoter. Transformation of Saccharomyces cerevisiae with the vector led to the formation of the G protein when cells were grown in the presence of galactose. Under these conditions the RSV G appeared as a 60- to 65-kDa glycosylated protein. Expression of the G cDNA in secretory mutants of S. cerevisiae yielded a protein of 35 kDa in a mutant unable to glycosylate secreted proteins and a 65-kDa polypeptide in a mutant unable to transport proteins beyond the endoplasmic reticulum. The RSV protein formed in the latter mutant was converted to a 60-kDa protein by endoglycosidase H. Our results show that yeast can recognize the internal signal sequence of RSV G protein and add glycosyl groups to the polypeptide in the endoplasmic reticulum. Evidence is presented for both N- and O-linked glycosylation of the virus glycoprotein.