Some Properties of the Particles of Three Tobravirus Isolates

When centrifuged in caesium chloride solutions, purified preparations of uncloned cultures of the cam and prn strains of tobacco rattle virus contained more than one component but single lesion isolates of each strain contained only one component with buoyant densities of 1.306 and 1.324 g./ml. respectively. The buoyant density of the sp5 strain of pea early-browning virus was 1.310. As determined by electron microscopy the diameters of the particle and the core were respectively 23 and 5 nm. for prn and about 21.5 and 4 nm. for both cam and sp5. The mol. wt of the single virus protein, obtained from each freshly purified virus and estimated by polyacrylamide gel electrophoresis, were 28,500 (cam and prn) and 24,000 (sp5). Each virus produced nucleoprotein particles of two predominant lengths and these yielded two RNA species whose mol. wt were proportional to those lengths. The mol. wt (× 10-6) estimated by polyacrylamide gel electrophoresis were 0.7 and 2.5 (cam), 1.0 and 2.5 (prn) and 1.3 and 2.5 (sp5).

At pH 8.6 the electrophoretic mobility of the long particle of cam was 16% greater than that of the short particles. However, the long particles of cam have few if any antigenic determinants not possessed by short particles.