Activation of Prunus necrotic ringspot virus and rose mosaic virus by RNa 4 components of some llarviruses

RNA extracted from rose mosaic virus (RMV) and from necrotic ringspot virus-G(NRSV) separated into four sedimenting components in sucrose density gradients. The components were designated RNAs 1, 2, 3, and 4 in order of decreasing sedimentation velocities. Sodium dodecyl sulfate (SDS)-denatured NRSV and RMV preparations showed a prominent protein species of about 25,000 daltons when electrophoresed in polyacrylamide gels. In addition, two closely migrating protein species of about 19,000 daltons were also observed in SDS-denatured RMV preparations. Preparations containing RNA 1+2+3 and preparations containing RNA 4 were obtained by two successive cycles of sucrose density gradient centrifugation. Neither preparation was infectious alone. Mixtures of RNA 1+2+3 from each virus became infectious, however, with the addition of homologous RNA 4. RMV protein also activated RMV-RNA 1+2+3 preparations. NRSV-RNA 4 efficiently activated RMV-RNA 1+2+3, but RMV-RNA 4 had very little ability to activate NRSV-RNA 1+2+3 even though it efficiently activated its homologous RNA 1+2+3 preparations. RNA 4 preparations from alfalfa mosaic virus (AMV) and citrus leaf rugose virus (CLRV) activated RMV-RNA 1+2+3. Comparable concentrations of RMV-RNA 4, however, failed to activate RNA 1+2+3 from AMV and from CLRV. RNA from CLRV, RMV, and citrus variegation virus (CVV) efficiently uncoated AMV particles. However, AMV-RNA and CLRV-RNA 4 uncoated CVV but not CLRV or RMV. The evidence presented indicated that viruses in the new Ilarvirus group [Shepherd, R. J., et al. (1976). Intervirology 6, 181–1841 have similar infectivity requirements; that is, mixtures of RNA 1+2+3 are not infectious but can be activated by either RNA 4 or coat protein.