  The question of how stiff polymers are able to pack into small containers is
particularly relevant to the study of DNA packaging in viruses. A reduced
version of the problem based on coarse-grained representations of the main
components of the system -- the DNA polymer and the spherical viral capsid --
has been studied by molecular dynamics simulation. The results, involving
longer polymers than in earlier work, show that as polymers become more rigid
there is an increasing tendency to self-organize as spools that wrap from the
inside out, rather than the inverse direction seen previously. In the final
state, a substantial part of the polymer is packed into one or more coaxial
spools, concentrically layered with different orientations, a form of packaging
achievable without twisting the polymer.
