THE UL10 GENE OF HERPES-SIMPLEX VIRUS-1 ENCODES A NOVEL VIRAL GLYCOPROTEIN, GM, WHICH IS PRESENT IN THE VIRION AND IN THE PLASMA-MEMBRANE OF INFECTED-CELLS

The herpes simplex virus 1 U(L)10 gene encodes a hydrophobic membrane protein dispensable for viral replication in cell culture (J. D. Baines and B. Roizman, J. Virol. 65:938-944, 1991). We report the following. (i) A fusion protein consisting of glutathione S-transferase fused to the C-terminal 93 amino acids of the U(L)10 protein was used to produce a rabbit polyclonal antiserum. The antiserum reacted with infected-cell proteins which formed in denaturing polyacrylamide gels a sharp band (apparent M(r) of 50,000) and a very broad band (M(r) of 53,000 to 63,000). These bands were not formed by lysates of U(L)10- virus or by lysates of infected cells boiled in the presence of sodium dodecyl sulfate before electrophoresis. (ii) The proteins forming both bands were labeled by [H-3]glucosamine, indicating that they were glycosylated. (iii) The U(L)10 protein in cells treated with tunicamycin formed a single band (apparent M(r) of 47,000) reactive with the anti-U(L)10 antibody, indicating that the 47,000-M(r) protein was a precursor of N-glycosylated, more slowly migrating forms of U(L)10. Treatment of the immunoprecipitate with endoglycosidase H increased the electrophoretic mobility of the 50,000-M(r) species to that of the 47,000-M(r) species, indicating that the 50,000-M(r) species contained high-mannose polysaccharide chains, whereas the proteins forming the 53,000- to 63,000-M(r) bands contained mature chains inasmuch as they were resistant to digestion by the enzyme. (iv) The U(L)10 protein of R7221 carrying a 20-amino-acid epitope formed only one band with an M(r) of 53,000. This band was sensitive to endoglycosidase H, suggesting that the epitope inserted in the R7221 U(L)10 protein may have interfered with glycosylation. (v) The U(L)10 protein does not contain a cleavable signal sequence inasmuch as the first U(L)10 methionine codon was reflected in the 50,000-M(r) protein. (vi) The U(L)10 protein is present in virions and plasma membranes of unfixed cells that were reacted with the polyclonal rabbit antibody. In accordance with the current nomenclature, the U(L)10 protein is designated glycoprotein M.