The structure of tobacco rattle virus ribonucleic acids: nature of the 3'-terminal nucleosides.

Tobacco rattle virus (TRV) is a multicomponent RNA plant virus which consists of two or more types of helical particle. All strains possess a long particle about I9 ° n m . long and one, or sometimes more, short particles whose lengths differ in different strains (Harrison & Woods, I966). Long particles of the virus are infectious in the absence of short but the product of the infection is long particle RNA and no mature particles are made (Frost, Harrison & Woods, t967). In contrast, short particles alone are non-infectious. The coat proteins of the different particles of any particular strain are identical (Harrison & Nixon, 1959; Lister & Bracker, 1969) and, in addition, Sanger (I968) has shown that, following infection with long and short particles of different strains, the virus produced has the serotype of the added short particles. These observations suggest that the genome of the short particle has the information for the coat protein of the virus whereas the information for an RNA replicase system which replicates all viral RNA species may be encoded in the genome of the long particle. If the various RNA species share a common replicase, they might be expected to have similar nucleotide sequences at their 3'-ends which act as binding sites for the enzyme. The CAM isolate of TRV consists of two particles, the shorter 52 nm. long and the longer i97 nm. long (Harrison & Woods, 1966 ). This strain is particularly convenient because its short particle is smaller than that of other strains in which there are only two size classes of particles. This simplifies the purification of the particles and the isolation of their RNA species. In this paper, we describe the purification of the particles from the CAM isolate of TRV and the isolation of their RNA species. We have shown that the RNA molecules from both particles are terminated at their 3' ends by unphosphorylated cytidine residues.