Polymerization studies on protein from the dahlemense strain of tobacco mosaic virus: Light scattering and related studies

Light-scattering and related studies on protein of Dahlmense strain of tobacco mosaic virus (DTMV) show that its polymerization characteristics are considerably different from those of TMV protein. At pH 6.0 in phosphate buffer (I = 0.1), the extent of polymerization of DTMV protein is greater than that of TMV protein, they are nearly the same at pH 6.25, and that of DTMV protein is less than that of TMV protein at pH 6.5. At pH 7.0 and 7.5, DTMV protein polymerizes more readily than TMV protein. Similar studies in phosphate buffer (I = 0.05) show that the extent of polymerization for DTMV protein is less than that of TMV protein at pH 6.0 and almost negligible at pH 6.25. Acid-base titration studies show that, upon temperature-mediated polymerization, about 2 H⁺ ions are bound per monomer of DTMV protein at pH 6.O.Electron microscope studies show that DTMV protein exists at room temperature as double discs and polymerized rods in phosphate buffer at pH 7.5, I = 0.1; at pH values below 6.5, DTMV protein is entirely in the form of polymerized rods. Velocity sedimentation studies of DTMV protein at room temperature are in agreement with these findings. At low temperatures, except at pH 7.5, most of the material sedimented with an s value of around 25 S. Thus, at low temperatures, except at pH 7.5, DTMV protein in solution is in the form of particles the size of double discs with an $\text{M}\text{?}{}_{\mathrm{<mtext>r</mtext>}}$ of 596,000 g/mole or even larger. Therefore, temperature-mediated polymerization of DTMV protein at pH values below 6.5 in phosphate buffer (I = 0.1) and below 6.25 in phosphate buffer (I = 0.05) involves particles at least as large as double discs as the starting material.