Identification and Characterization of the Protein Product of Gene 71 in Equine Herpesvirus 1

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Abstract
Equine herpesvirus 1 (EHV-1) strain Ab4 gene 71 is predicted to encode a primary product with a M r of 80.1K. We have previously constructed a deletion/lacZ insertion mutant, ED71, and demonstrated that gene 71 is dispensable for growth of virus in cell culture. We have now constructed a gene 71 revertant, Re71. To identify and characterize the product of gene 71, we produced a specific antiserum, anti-71, against a β-galactosidase fusion protein containing the carboxy terminus of the gene 71 polypeptide. Using the anti-71 serum, mutant ED71 and the revertant Re71, we have demonstrated that gene 71 encodes a 192K polypeptide. Experiments with glycosylation inhibitors revealed that the protein product of gene 71 is N-glycosylated and heavily O-glycosylated. When the 192K polypeptide is synthesized in the presence of monensin, the M r of the polypeptide is reduced to 80K, the predicted unmodified M r of the gene 71 polypeptide. The gene 71 product is found in virions and L particles in a fully processed form that runs as a diffuse band in electrophoresis, with a M r in excess of 200K. Immunofluorescence and virion surface labelling experiments showed that the polypeptide product of gene 71 is located on cellular membranes and the virion envelope. A time course of infection confirmed that gene 71 is regulated as a leaky late gene in infected cells. Finally, using wild-type EHV-1 Ab4, mutant ED71, revertant Re71 and two antibodies (P19 against EHV-1 glycoprotein gp300, and anti-71) we conclusively demonstrated that gene 71 encodes gp300. This contradicts published results with P19 alone, which indicated gp300 was the product of EHV-1 gene 28.

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