A Characterization of Alfalfa‐Mosaic‐Virus Protein Polymerization in the Presence of Nucleic Acid

Abstract

The polymerization of alfalfa mosaic virus (AMV) protein in the presence of homologous nucleic acids and a number of other natural and synthetic nucleic acids was studied. The conditions for optimal assembly were pH 6.0 and low ionic strength (I = 0.1 M) at room temperature, irrespective of the type of nucleic acid. The resulting nucleoprotein particles exhibited the same structural characteristics as the virus. This information emerged from optical diffraction and computer filtering of electron micrographs from the reconstituted particles. Irrespective of the type of nucleic acid present the polymerization of the protein resulting in a nucleoprotein particle is a cooperative process. Evidence for this was obtained by nitrocellulose filter binding assay, sodium dodecylsulfate/polyacrylamide gel electrophoresis, sedimentation velocity and EM of the reaction mixtures. The rates and efficiencies of reconstitution were of the same order of magnitude for a number of RNA. Sedimentation data derived from AMV protein and AMV RNA mixtures suggested the existence of a specific nucleation product in the 1st stage of assembly. The results are discussed in terms of a tentative model of the assembly, in which at least 2 different steps (nucleation and elongation) can be distinguished, each characterized by an association constant.