Some properties of the virions of galinsoga mosaic virus

An increasing number of plant viruses with stable isometric virions are being described, but their classification will be possible only when the biochemical and biophysical properties of these virions are better known. This paper reports additional properties of one such virus, namely Galinsoga mosaic virus (GMV), which was originally isolated from the roots of an annual weed species Galinsoga parviflora Cav. (1) in Queensland, but has a wide host range and is soil-borne (2). Virions of GMV were purified as described by Behncken (1) using the primary leaves of bean (Phaseolus vulgaris) as both propagation and assay host. Virion concentration was correlated with symptom severity; the most concentrated preparations were obtained from the leaves of the cultivars Hawkesbury Wonder, Canadian Wonder and Royal Windsor, and least from Blue Lake, Epicure, Purple King, Redland Pioneer and Westralia. With infective sap diluted to give between 5 and 100 lesions per leaf, there was a linear correlation between sap concentration and lesion num bers, suggesting that one sort of particle determined infectivity. Properties of GMV virions were assessed by the techniques used by Skotnicki et al. (3). Virion preparations had ultraviolet absorption spectra of nucleoprotein suspensions with an A260/A2soratio of 1.66, indicating an RNA content of about 22%. When negatively stained in 1% uranylacetate, the virions were isometric with a rounded profile and a diameter of 28 nm (measured against the lattice of bovine catalase crystals). The virions had a sedimentation coefficient of 117.9 ± 2.1 S20, w(3 estimates). Some preparations also contained a component that sedimented more slowly (f. 48S) and had a much smaller A260/A280 ratio than the virions. GMV genome RNA, compared electrophoretically with 23S and 16S ribosomal RNA of E. coli in 0.5, 1.5 and 3.0% polyacrylamide gels, had an estimated molecular weight of 1.55 x 106. This RNA had a molar base composition (5 analyses) of G 24.8 ± 0.3; A 28.1 ± 0.6; C 21.8 ± 1.0; U 25.3 ± 0.7. GMV virion protein migrated as a single species in PAGE experiments and had a mean molecular weight (3 estimates) of 36.4 (± 1.8) x 10 • The percentage molar composition and 'best fitting' integral number of amino acids were assessed from samples hydrolysed for 1, 2 and 4 days and others oxidised with performic acid. The resulting estimates were Ala 7.07 (26), Arg 4.44 (16), Asx 9.30 (34), Cys 1.61 (6), Glx 8.08 (29), Gly 9.97 (36), His 2.14 (8), lie