Structural Aspects of Tobacco Mosaic Virus

Polymerization-depoly-merization of tobacco mosaic virus protein. I. Kinetics

It was shown that a reversible endothermic association of TMV protein subunits (A protein) can take place at pH values below the isoelectric point as well as at pH 6.5. The polymerization occurring below the isoelectric point was found to be more complex than that at pH 6.5 probably because products other than the usual TMV-like rods were formed in addition to those rods and also because side-to-side aggregation of the rods took place readily. Kinetic studies indicated that polymerization can be treated as a second-order linear condensation. The rate of polymerization was found to be a critical function of pH, having a maximum value near pH 4.3. This behavior is at variance with the hypothesis that hydrogen-bonded carboxyl pairs play a dominant rate-determining role in the association of subunits. The dependence of the rate on pH was interpreted to indicate that electrostatic forces between subunits are a significant controlling factor in the polymerization of TMV protein.

Polymerization of tobacco mosaic virus protein without and with hydrogen ion binding

When tobacco mosaic virus (TMV) protein is polymerized at pH values above 7 in unbuffered solutions, either by raising temperature at constant ionic strength or by increasing ionic strength at constant temperature, a 20 S component is formed having bound only the very small amount of H+ ion supplied by the unpolymerized protein. When hydrogen ion is added by titration during polymerization so as to keep pH constant, as would occur automatically if a buffer were present, a 20 S component is formed with one H+ ion bound each for half of the subunits. Thus, a 20 S form with and a 20 S form without bound H+ ion exist. Furthermore, the 20 S form without bound H+ ion binds H+ ion when supplied by titration to produce a 20 S form with the same amount of bound H+ ion as when H+ ion is supplied during the polymerization.

Action of urea on tobacco mosaic virus. II. The bonds between protein subunits

The rate of urea degradation is not uniform over the tobacco mosaic virus (TMV) rod, as might be expected since the protein subunits appear to be chemically identical. Only two stable intermediates are formed; the four components with sedimentation constants, S(40) (20), about 80, 120, 140, and 165 correspond to the two intermediates with and without RNA tails. Analysis of the reaction kinetics for the disappearance of whole virus and of the first intermediate was made in terms of a new hypothesis concerning protein bonding.