Polymerization-Depolymerization of Tobacco Mosaic Virus Protein: Refinement of a Model

Abstract

Detailed analysis of the difference between “low temperature,” pH insensitive, and “high temperature,” pH sensitive polymerization of TMV A protein has led to a revision of the model originally proposed by Lauffer. All of the basic postulates are retained, but the positions of the various types of water-interacting center on the surface of the monomeric unit have been changed. In the new model, lateral polymerization will take place at “low temperatures” and will lead to the formation of double discs. At “high temperatures,” diagonal polymerization will take place leading to open helices, possibly like those shown by the PM 2 strain. At still higher temperatures, the open helices polymerize side by side to form closed cylindrical helices similar to TMV. A consequence of this theory is that polymerization at pH 7.5 should result primarily in the formation of double discs and polymerization at pH values below 6.5 should form open helices and complete helical cylinders. Preliminary optical rotatory dispersion measurements and electron microscope results are consistent with this prediction.