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 Rk₁₃ cell line (TCgM) that stably expressed EHV-1 gM was constructed. Proteins with apparent M_rs 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 (L11ΔgM) bearing an Escherichia coli lacZ gene inserted into the EHV-1 strain RacL11 gM gene (open reading frame 52) was purified, and cells infected with L11ΔgM did not contain detectable gM. L11ΔgM 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 L11ΔgM was grown on the complementing cell line TCgM and titrated on noncomplementing cells. L11ΔgM also exhibited slower penetration kinetics compared with those of the parental EHV-1 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-1 from cell to cell.