  Capsids of many viruses assemble around nucleic acids or other polymers.
Understanding how the properties of the packaged polymer affect the assembly
process could promote biomedical efforts to prevent viral assembly or
nanomaterials applications that exploit assembly. To this end, we simulate on a
lattice the dynamical assembly of closed, hollow shells composed of several
hundred to 1000 subunits, around a flexible polymer. We find that assembly is
most efficient at an optimum polymer length that scales with the surface area
of the capsid; significantly longer than optimal polymers often lead to
partial-capsids with unpackaged polymer `tails' or a competition between
multiple partial-capsids attached to a single polymer. These predictions can be
tested with bulk experiments in which capsid proteins assemble around
homopolymeric RNA or synthetic polyelectrolytes. We also find that the polymer
can increase the net rate of subunit accretion to a growing capsid both by
stabilizing the addition of new subunits and by enhancing the incoming flux of
subunits; the effects of these processes may be distinguishable with
experiments that monitor the assembly of individual capsids.
