Role of glycosylation in transport of vesicular stomatitis virus envelope glycoprotein. A new class of mutant defective in glycosylation and transport of G protein.

A temperature-sensitive mutant (ts gamma 1) of the Cocal serotype of vesicular stomatitis virus synthesizes at the permissive temperature (32 degrees C) a glycoprotein G whose size is smaller (Mr 68,000) than the wild-type (Mr 71,000) and that renders the virion thermolabile. At the nonpermissive temperature (39 degrees C), reduced amounts of noninfectious virus-like particles deficient in G protein were produced. The size of the intracellular G protein was further decreased (Mr 64,000) at the nonpermissive temperature. Biochemical studies including sugar labeling, tryptic peptide analysis, and NH2-terminal sequence analysis of the various glycoproteins suggest that at 32 degrees C a G protein containing a single glycosidic moiety is synthesized. The G protein containing only 1 oligosaccharide residue is transported to the cell surface and is incorporated in infectious virus particles. In contrast, the G protein synthesized at 39 degrees C is nonglycosylated and fails to reach the cell surface. These results suggest that glycosylation of G protein is essential for its transport to the cell surface, and the presence of a single carbohydrate chain is sufficient for this purpose.