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Some physico-chemical studies on two icosahedral viruses Kalmakoff, James


An investigation into the physical and chemical properties of two icosahedral viruses was undertaken, one a plant virus, carnation ringspot virus (CRSV), and the other an insect virus, Tipula iridescent virus (TIV). These viruses were studied using accepted chemical and biophysical methods and parameters such as amino acid composition, nucleotide composition, sedimentation coefficients, diffusion coefficients, molecular weights, hydration, and morphology in the electron microscope were determined. CRSV could be purified by frontal elution from AG1-X8 quaternary ammonium anion exchange resin with a NaCl-phosphate buffer, pH 6.8. The composition of CRSV based on nucleotides and amino acids recovered was 20.48% and 79.52% protein. Amino acid analyses indicated that the subunit protein was composed of approximately 347 amino acid residues with a subunit molecular weight of 38,000. The sedimentation and diffusion coefficients were 132 x 10¯¹³ sec and 1.48 x 10¯⁷ cm² /sec, respectively. A molecular weight based on the above two parameters was 7.07 x 10⁶. An uncorrected extinction coefficient at 260 mµ for the virus was found to be 6.46 cm² /mg virus. The frictional ratio calculated from the hypothetical diffusion coefficient of the anhydrous particle and the observed diffusion was 1.16. Assuming the virus particle to be spherical the degree of hydration was O.38 g water/g of virus. TIV was purified by sedimentation through a 5-40% sucrose density gradient. The particle molecular weight of TIV based on a sedimentation coefficient of 2200 x 10¯¹³ sec and a diffusion coefficient of 3.3 x 10¯⁸ cm²/sec was 5.51 x 10⁸ g/mole. A frictional ratio of 1.22 was calculated and the value of 0.57 g water/g virus was obtained assuming the deviation of the frictional ratio from unity was due to hydration. The DNA content based on total inorganic phosphorous liberated was 19 ± 0.2%. At 260 mμ the virus gave an uncorrected absorbance of 18.2 cm² /mg virus and a light scattering corrected absorbance of 9.8 cm² /mg virus. Amino acid analyses of the virus protein revealed a remarkable similarity to Sericesthis iridescent virus (SIV), suggesting a strain relationship. The relative amounts of all the amino acids of these two viruses, with the exception of arginine, are within experimental error. The possibility that the four iridescent insect viruses Sericesthis iridescent virus (SIV), mosquito iridescent virus (MIV), and Chilo iridescent virus (CIV) bear a strain relationship is discussed.

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