Expression cloning and antigenic analysis of the nucleocapsid protein of equine arteritis virus

A series of recombinant fusion proteins derived from equine arteritis virus (EAV) open reading frame (ORF) 7 have been used to define the immunoreactive region of the viral nucleocapsid (N) protein. Reactivities of recombinant N fusion proteins with post-infection equine sera in immunoblots and ELISAs indicate that the major nucleocapsid protein epitope is located within amino acid residues 1–69. In ELISAs two recombinant nucleocapsid fusion proteins containing residues 1–69 (rN1–69) and 1–28 (rN1–28) discriminated between pre- and post-infection, and pre- and post-vaccination serum samples. Additionally rN1–69 and rN1–28 detected seroconversions following vaccination with a killed virus preparation, even in the absence of a detectable virus neutralising response. Although a good correlation existed between virus neutralising antibody and rN1–69 ELISA positive values in post-infection sera, all the rN proteins failed to induce any virus neutralising response in immunised rabbits.