Localization of two cellular forms of the vesicular stomatitis viral glycoprotein

Abstract

Two cell-associated forms of the glycoprotein (G) of vesicular stomatitis virus, termed G_1 and G_2, have been resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. G_1 has the higher electrophoretic mobility, but both forms migrate more slowly than G protein synthesized in a wheat germ cell-free system (G_0), which presumably is the unglycosylated form. G_1 is a kinetic precursor of the G_2 form, and the apparent cause of the electrophoretic difference between the two species is the presence of N-acetylneuraminic acid on the G_2 form. Conversion of G_1 to G_2 occurs 10 to 20 min prior to the appearance of the G_2 form of the protein on the cell surface. This suggests that the G protein may be completely glycosylated several minutes prior to its migration to the cell surface and that glycosylation is not the limiting step in its maturation. No glycoprotein comigrating with G_0 can be detected in the infected cells, even after 5-min labeling periods; this suggests that partial clycosylation of G occurs concomitantly with or immediately after its synthesis.