Viral protein synthesis in mouse hepatitis virus strain A59-infected cells: effect of tunicamycin

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Abstract
Eight protein species were identified in virions of mouse hepatitis virus strain A59 (MHV-A59). Based on their sizes, prosthetic groups and locations in virions, these proteins were designated gp180/E2, gp90/E2, pp54/N gp26.5/E1, gp25.5/E1, p24/E1, p22/X and p14.5/Y. The positions of the last 2 proteins in virions are not known. Host protein synthesis in Sac(-) [mouse] cells infected with MHV-A59 was inhibited and the following novel proteins appeared: gp150, gp90, p54, gp26.5, gp25.5, p24, p22 and p14.5. Except for gp150, these polypeptides all co-electrophoresed with MHV-A59 structural proteins. All of these proteins could be immunoprecipitated with a convalescent mouse serum or a rabbit antiserum raised against purified disrupted virus. After a 15-min pulse of infected cells with radioactive amino acids at 7 h postinfection, gp90 was not detected; gp26.5 and gp25.5 were only labeled to a small extent. During a subsequent chase period gp150 was processed to gp90; the radioactivity in gp26.5 and gp25.5 increased concomitantly with a reduction of label in p24. Tunicamycin, an antibiotic which inhibits the synthesis of glycopeptides bearing N glycosidically linked oligosaccharides, prevented the appearance of gp150 in MHV-A59-infected cells. Instead, a 110,000-dalton protein accumulated. The syntheses of the smaller viral glycoproteins gp26.5 and gp25.5 were resistant to this drug, indicating that these glycosylations were of the O glycosidical type. Although the production of infectious virus in tunicamycin-treated cells was inhibited by > 99%, release of noninfectious viral particles continued. An analysis of these particles revealed that they lacked the peplomeric glycoproteins gp90/E2 and gp180/E2. Obviously, although the surface projections were not essential for budding of virus particles from the cells, they were required for infectivity.