A variant of western equine encephalitis virus with nonglycosylated E3 protein

A variant clone (At/A125) of western equine encephalitis virus was isolated from a line of mosquito cells persistently infected with a temperature-sensitive parent strain, A125. Variant-infected cells produced an altered form of PE2 protein which migrated with a higher electrophoretic mobility than wild type or A125 PE2. The altered PE2, like PE2 of wild type, was precipitated by anti-envelope proteins serum but not by anti-E1 serum. In pulse-chase experiments the altered PE2 protein was shown to yield E2 of normal electrophoretic mobility in SDS-polyacrylamide gel electrophoresis. The unglycosylated form of the altered PE2 synthesized in the presence of tunicamycin migrated at the same position as the unglycosylated PE2 obtained from tunicamycin-treated, parent strain-infected cells. This suggested that migration difference might be ascribable to incomplete glycosylation of PE2, possibly of its E3 component. E3 is released into culture fluid of wild-type-infected cells as an approximately 11-kd glycoprotein, while variant-infected culture fluid yielded a smaller, apparently virus-specific protein. The protein could not be labeled with [3H]mannose, suggesting that the polypeptide moiety of E3 in the variant infected cells failed to be glycosylated. The parent strain, A125, and a revertant of the variant, At/A125/rev, did not synthesize such altered PE2 and E3 proteins. The growth of At/A125 in mosquito cells was similar to that of parent or wild type but depressed in vertebrate cells.