  Single-stranded (ss) RNA viruses self-assemble spontaneously in solutions
that contain the viral RNA genome molecules and the viral capsid proteins. The
self-assembly of empty capsids can be understood on the basis of free energy
minimization of rather simple models. However, during the self-assembly of
complete viral particles in the cytoplasm of an infected cell, the viral genome
molecules must be selected from a large pool of very similar host messenger RNA
molecules. It is known that the assembly process takes the form of preferential
heterogeneous nucleation of capsid proteins on viral RNA molecules ("selective
nucleation"). Recently, a simple mathematical model was proposed for the
selective nucleation of small ssRNA viruses. In this paper we present a
statistical physics analysis of the thermal equilibrium and kinetic properties
of that model and show that it can account, at least qualitatively, for
numerous observations of the self-assembly of small ssRNA viruses.
