Purified preparations of several isolates of tomato ring-spot virus were shown by rate-zonal centrifugation in sucrose and equilibrium centrifugation in CsCl to be composed of two individual nucleoprotein components. Acrylamide-gel electrophoresis showed that the lighter (middle) component contained a nucleic acid (RNA 2) that was distinct from the species (RNA 1) contained in the heavier (bottom) component. The bottom was more infectious than the middle component and infectivity was enhanced by mixing the components, indicating that the virus genome is divided between component types. Similar results were obtained from infectivity tests on the two nucleic acids. The nucleic acid contents of the middle and bottom components were about 40 and 41%, respectively. The average molecular weights of RNA 2 and RNA 1 from three virus isolates, as determined by acrylamide-gel electrophoresis, were 2.5 and 2.6 × 106, respectively. Molecular complexing between the RNA species during electrophoresis was prevented with the use of formamide. The single protein subunit from the same three isolates had an average molecular weight of about 58 000. Serological comparisons of five tomato ring-spot isolates associated with diseases of fruit trees and grapevines indicated that only the grape yellow vein strain was antigenically distinct. These and other properties indicate that this virus is similar to other members of the nepovirus group.
Serological Evidence for the Presence of Prunus Necrotic Ring Spot Virus in Stone Fruits with Particular Reference to Peach
