Kinetic study of the self-assembly of brome mosaic virus capsid

The protein of brome mosaic virus can self assemble in-vitro to form empty capsids. In the absence of RNA at pH=7 and 0.5 M KCl there is a dynamic equilibrium between monomers and oligomers. At pH=5 the protein assembles into empty capsids. The kinetics of this assembly, triggered by pH jump from neutral to acidic pH, was investigated by X-ray and light scattering.Cryoelectron microscopy observations suggested that reconstitution is achieved by progressive incorporation of small building units in a spherical shell. This hypothesis has been tested by the analysis of the scattering data in terms of four classes of incomplete capsids represented as spherical shells with holes of different sizes. The time dependence of the population of each class was determined by a least squares analysis of the experimental data. Although the basic polymerizing unit has not been uniquely characterized, the results are compatible with a dimer for this species. The characteristic times for capsid assembly are found to vary as the inverse of the square of the concentration.