ANALYSIS OF THE STRUCTURE AND BIOLOGICAL ACTIVITY OF PRUNUS NECROTIC RINGSPOT AND APPLE MOSAIC VIRUSES USING MONOCLONAL ANTIBODIES

Abstract

Monoclonal antibodies reactive with two ilarviruses, Prunus necrotic ringspot virus (PNRSV) and apple mosaic virus (ApMV) were utilized to determine the structural and biological properties of the viruses. Three monoclonal antibodies (Mabs 1, 2 and 3) which reacted only to ApMV in various ELISA tests were found to bind to conformation independent epitopes which are hidden between or within viral subunits. Three other monoclonal antibodies (Mabs 5, 6 and 7) which reacted only to PNRSV in various ELISA tests were found to bind to conformation dependent, externally located epitopes. One monoclonal antibody, Mab 4, which reacted with both viruses was found to bind to a conformation dependent, partialiy hidden epitope on ApMV, but a conformation independent, external ,Titope on PNRSV. Further, the three ApMV-specific antibodies reacted with viral coat protein in Western blots. None of the three PNRSV-specific antibodies reacted with viral coat protein in Western blots. Mab 4, however, did react with PNRSV coat protein but not ApMV coat protein in Western blots. Fragments of PNRSV coat protein were generated by proteolysis, and, in Western blots, all were found to be bound by Mab 4. Thus, attempts to isolate a specific polypeptide containing the epitope were unsuccessful. In neutralization of infectivity studies, Mab 4 blocked PNRSV infectivity although the antibody did not precipitate the virus in Ouchterlony double diffusion tests. This suggests that Mab 4 may bind to an epitope located in a region of the coat protein necessary for infection. Although not yet examined for PNRSV, a characteristic of other ilarviruses is coat protein dependent initiation of infection, where coat protein, or a subgenomic RNA which codes for coat protein, is required for the RNAs to be infectious. Thus, Mab 4 may be a useful probe for studying this process in PNRSV and other ilarviruses.