Multidense satellite of tobacco ringspot virus: A regular series of components of different densities

Abstract

Satellite of tobacco ringspot virus (S-TRSV) is composed of at least 11 and possibly as many as 14 components, ranging in density from ϱ = 1.408 through ϱ = 1.529. Each component differs in buoyant density from its nearest neighbor by approximately †ϱ = 0.009. The buoyant density of middle component of tobacco ringspot virus is approximately ϱ = 1.423, about †ϱ = 0.015 greater than that of the S-TRSV component with the lowest buoyant density. Bottom component of tobacco ringspot virus is composed of two populations, one population with an average ϱ = 1.507 and the other with an average ϱ = 1.518. The buoyant densities found in a S-TRSV population are not artifacts caused by CsCl, but are characteristic of the population before the particles are exposed to CsCl, and correlate with the position of the particles sedimenting in a sucrose gradient. Since some TRSV particles are always in S-TRSV preparations, the three components with densities approximating those of bottom and middle, may not be S-TRSV. Thus S-TRSV is composed of at least 11, but possibly 14 components. A high proportion of satellite to TRSV in inoculum resulted in a high proportion of S-TRSV in the infected plants. Plants inoculated with TRSV and “low-density” S-TRSV yielded both “high” - and “low-density” S-TRSV as well as TRSV. No significant difference was detected in the base ratio of the nucleic acids within TRSV (strain WS)—middle or bottom components—and the base ratio of the nucleic acid strands within S-TRSV that had been activated by TRSV (strain WS). The data fit with the following view. All S-TRSV particles contain numerous nucleic acid strands of uniform size, each strand approximating 86,000 daltons. Each S-TRSV particle of the lowest buoyant density has approximately 12 nucleic acid strands; each S-TRSV particle of higher density has one more nucleic acid strand than its nearest neighbor of lower density. Most members of this continuous series are consistently found in purified preparations of S-TRSV. Particles with the highest density contain approximately 25 nucleic acid strands per particle.