Genetic variation in open reading frame 2 of field isolates and laboratory strains of equine arteritis virus

The open reading frame 2 (ORF2) of three laboratory strains, the live attenuated vaccine virus, and 18 field isolates of equine arteritis virus (EAV) from Europe and North America was sequenced. The ORF2 of EAV encodes the G(S) protein that is abundantly expressed in infected cells but constitutes less than 2% of the virion protein mass. Variation of ORF2 among the isolates facilitated phylogenetic analysis that largely confirmed results of an earlier study based on sequence divergence of ORF5 of the same isolates of EAV, despite exposure of the proteins encoded by ORF2 (G(S)) and ORE5 (G(L)) to potentially different selective pressures in vivo. The data indicate that the G(S) protein is highly conserved between isolates, considerably more so than the G(L) protein, consistent with an important role of the G(S) protein in virus replication.