The purification and characterization of the type, nasturtium ringspot and petunia ringspot strains of broad bean wilt virus are described. The use of sucrose throughout purification reduced losses due to aggregation of the virus particles. Electron microscopy of virus preparations revealed particles which were apparently hexagonal in outline and approx. 27 nm in diam. Each virus had three sedimenting components, top (T), middle (M) and bottom (B), indistinguishable from those of cowpea mosaic virus (CPMV) in co-sedimentation experiments. The sedimentation coefficients, of PRSV were 56S (T), 95S(M) and 116S(B). The buoyant densities of M and B components of BBWV, NRSV and PRSV in CsCl + 2.34% (w/v) Igepon T73 were approx. 1.40 and 1.44 g/ml respectively. B components of the viruses contained a single RNA species (RNA-1) of mol. wt. 2.0 ± 0.1 × 10 and approximate molar percentage base ratio of 26% guanine, 30% adenine, 17.5% cytosine and 26.5% uracil. M components of the viruses contained a single RNA species (RNA-2), mol. wt. 1.5 to 1.6 × 10. The base ratios of RNA-1 and RNA-2 of BBWV were very similar. Mixtures of RNA-1 and RNA-2 (or M and B components) were more infective than the separate RNA species (or virus components). Mol. wt. of the formaldehyde-denatured RNA species of BBWV, NRSV and PRSV were very similar to those of CPMV. BBWV, NRSV and PRSV contained two species of polypeptide, mol. wt. 42000 and 26000.

These properties in conjunction with serological evidence indicate that the viruses are closely related strains. The similarity between some of the properties of BBWV, NRSV and PRSV and those of CPMV is discussed.


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