The equine herpesvirus 1 glycoprotein gp21/22a, the herpes simplex virus type 1 gM homolog, is involved in virus penetration and cell-to-cell spread of virions

Experiments to analyze the function of the equine herpesvirus 1 (EHV-1) glycoprotein gM homolog were conducted. To this end, an Rk(13) cell line (TCgM) that stably expressed EHV-1 gM was constructed. Proteins with apparent M(r)s of 46,000 to 48,000 and 50,000 to 55,000 were detected in TCgM cells with specific anti-gM antibodies, and the gM protein pattern was indistinguishable from that in cells infected with EHV-1 strain RacL11, A viral mutant (L11 Delta gM) bearing an Escherichia coli lacZ gene inserted into the EHV-I strain RacL11 gM gene (open reading frame 52) was purified, and cells infected with L11 Delta gM did not contain detectable gM. L11 Delta gM exhibited approximately 100-fold lower titers and a more than 2-fold reduction in plaque size relative to wild-type EHV-1 when grown and titrated on noncomplementing cells. Viral titers were reduced only 10-fold when L11 Delta gM was grown on the complementing cell line TCgM and titrated on noncomplementing cells. L11 Delta gM also exhibited slower penetration kinetics compared with those of the parental EHV-I RacL11. It is concluded that EHV-1 gM plays important roles in the penetration of virus into the target cell and in spread of EHV-I from cell to cell.