CLONING AND EXPRESSION OF AN ANTIGENIC DOMAIN OF GLYCOPROTEIN GE OF PSEUDORABIES VIRUS IN ESCHERICHIA-COLI AND ITS USE AS ANTIGEN IN DIAGNOSTIC ASSAYS

Use of a combination of an effective gE gene-deleted pseudorabies viru s (PRV) vaccine with a companion diagnostic kit for PRV glycoprotein g E has proven successful in several pseudorabies-eradication programs. To produce a large quantity of functional gE protein for development o f a PRV-gE diagnostic kit, an Escherichia coli expression system conta ining the distal region of the PRV-gE gene of a PRV strain CF was cons tructed. The expressed protein contained 134 amino acids of gE protein (amino acids 77-210) fused to a 19-amino acids tag containing 6 histi dine residues. After induction, a truncated PRV-gE polypeptide of 18-k d was expressed to about 20% of the total E coli proteins. Results of immunoblot analysis indicated that this E coli-produced PRV-gE protein reacted specifically with serum from PRV-hyperimmunized pigs and from field PRV-infected pigs, but not with serum samples from specific-pat hogen-free pigs or pigs inoculated with gE-deleted PRV vaccine. These data indicate that, although the recombinant gE protein is produced in E coli, it still retains the antigenicity of the viral gE glycoprotei n. Comparison between the recombinant gE protein, using immunoblot ana lysis with a commercial gE ELISA containing natural PRV-gE protein, re vealed comparable test performance. This finding indicated that recomb inant gE protein produced by E coli can be used for development of a c ompanion serologic assay for a PRV-gE gene-deleted vaccine.