Equine herpesvirus 1 (EHV-1) glycoprotein M: Effect of deletions of transmembrane domains

Equine herpesvirus 1 (EHV-1) recombinants that carry either a deletion of g lycoprotein M (gM) or express mutant forms of gM were constructed. The reco mbinants were derived from strain Kentucky A (KyA), which also lacks genes encoding gE and gl. Plaques on RK13 cells induced by the gM-negative KyA we re reduced in size by 80%, but plaque sizes were restored to wild-type leve ls on gM-expressing cells. Electron microscopic studies revealed a massive defect in virus release after the deletion of gM in the gE- and gl-negative KyA, which was caused by a block in secondary envelopment of virions at Go lgi vesicles. Recombinant KyA expressing mutant gM with deletions of predic ted transmembrane domains was generated and characterized. It was shown tha t mutant gM was expressed and formed dimeric and oligomeric structures. How ever, subcellular localization of mutant gM proteins differed from that of wild-type gM. Mutant glycoproteins were not transported to the Golgi networ k and consequently were not incorporated into the envelope of extracellular virions. Also. a small plaque phenotype of mutant Viruses that was indisti nguishable from that of the gM-negative KyA was observed. Plaque sizes of m utant viruses were restored to wild-type levels by plating onto RK13 cells constitutively expressing full-length EHV-1 gM, indicating that mutant prot eins did not exert a transdominant negative effect on wild-type gM. (C) 200 0 Academic Press.