STRUCTURAL PROTEINS OF EQUINE ARTERITIS VIRUS

We have recently shown that the genome of equine arteritis virus (EAV) contains seven open reading frames (ORFs). We now present data on the structural proteins of EAV and the assignment of their respective genes. Virions are composed of a 14-kDa nucleocapsid protein (N) and three membrane proteins designated M, G(S), and G(L). M is an unglycosylated protein of 16 kDa, and G(S) and G(L) are N-glycosylated proteins of 25 and 30 to 42 kDa, respectively. The broad size distribution of G(L) results from heterogeneous N-acetyllactosamine addition since it is susceptible to digestion by endo-beta-galactosidase. Using monospecific antisera as well as an antivirion serum, and by expression of individual ORFs, the genes for the structural proteins were identified: ORF 7 codes for N, ORF 6 for M, ORF 5 for G(L), and ORF 2 for G(S). With the exception of G(S), the proteins are about equally abundant in EAV virions, being present at a molar ratio of 3 (N):2 (M):3 (G(L)). The G(S) protein, which is expressed at a level similar to that of M in infected cells, is strikingly underrepresented in virus particles (I to 2%). Our data justify a distinct taxonomic position for EAV, together with lactate dehydrogenase-elevating virus and simian hemorrhagic fever virus; although coronavirus- and toroviruslike in features of transcription and translation, the virion architecture of EAV is fundamentally different.