DIFFERENT POINT MUTATIONS WITHIN THE CONSERVED N-GLYCOSYLATION MOTIF OF PSEUDORABIES VIRUS GLYCOPROTEIN-M RESULT IN EXPRESSION OF A NONGLYCOSYLATED FORM OF THE PROTEIN

Glycoprotein M (gM) constitutes one of the rare examples of a nonessen tial glycoprotein conserved throughout all herpesvirus subfamilies. Wh ereas gM in wild-type pseudorabies virus (PrV) strains carries an N-gl ycan, gM of the attenuated strain Bartha is not glycosylated due to a point mutation in the N-glycosylation motif. Since PrV Bartha lacks gl ycoproteins E and I and carries a mutated gC, we analysed glycosylatio n of gM in isogenic PrV glycoprotein deletion mutants. Whereas gM was glycosylated normally in most mutants, two independent gC deletion mut ants and a gI mutant expressed a nonglycosylated form of gM. DNA seque nce analyses revealed the presence of point mutations in the N-glycosy lation consensus motif. Surprisingly, mutations in strain Bartha, the two gC-deletion mutants and the gI mutant proved to be different, alth ough all affected the N-glycosylation motif. Thus, our data show that different, apparently independent point mutations cause expression of nonglycosylated gM.