Abstract
The molecular weight of the nucleic acid is a basic property of a virus, and has been shown to be of great value for classifying animal viruses (Bellett, 1967). However, this property is known for few plant viruses. In the potato virus X group, for example, only the RNA of potato virus X (PVX) itself has a known molecular weight. The reported value (2.1 x 106) has been calculated from the total particle weight of the virus and its phosphorus content (Knight, 1963).
Recently electrophoresis in acrylamide gels of low concentration has been successfully used to estimate the molecular weights of large RNA molecules (Loening, 1968; 1969). Studies including the RNAs of five plant viruses have been reported by Bishop, Claybrook & Spiegelman (1967), and the RNA of tobacco mosaic virus (TMV) has been used as a marker in the re-examination of the molecular weight of poliovirus RNA (Tannock, Gibbs & Cooper, 1970).