PROPERTIES OF COWPEA CHLOROTIC MOTTLE VIRUS ITS PROTEIN AND NUCLEIC ACID

The hydrodynamic behavior of cowpea chlorotic mottle virus (CCMV) suggests that it exists as two forms, depending on pH. The virus, which contains about 24% RNA, has a sedimentation coefficient of 88.3 S and a diffusion coefficient of 1.50 ± 0.04 × 10-7 cm2/sec at pH 5.0. At neutrality, the sedimentation coefficient is 77.8 S and the diffusion coefficient is 1.37 ± 0.03 × 10-7 cm2/sec. The two forms of the virus are interconvertible in terms of gross physical behavior, but once the virus has been converted to the slowly sedimenting or swollen form, infectivity is lost because the nucleic acid is ruptured during swelling. The hydrodynamic molecular weights of the normal and swollen forms are 4.6 ± 0.1 and 4.4 ± 0.1 × 106 avograms, respectively. The molecular weight derived by multiplying the number of structure units by the molecular weight of the chemical unit, obtained from amino acid analysis, plus the weight of RNA, is also about 4.6 × 106 avograms. The virus has an isoelectric point of pH 3.65 at μ = 0.1. When centrifuged to equilibrium in CsCl, CCMV forms two populations of particles interpreted as being monomers and tetramers. The nucleic acid has a base ratio of C:A:G:U = 20.3:25.3:26.4:28.2. Phenol extracts of virus yield three sedimenting species of RNA with sedimentation coefficients of 23.1, 18.2, and 12.6 S. Only the fastest sedimenting class of the RNA is infectious and this class becomes labeled with 32P at a greater rate than the two more slowly sedimenting classes, which are probably derived from the infectious class by a single break. The physical condition of the RNA is dependent on the in vivo and in vitro history of the virus. © 1968.