  The ability of double-stranded DNA or RNA to locally melt and form kinks
leads to strong non-linear elasticity effects that qualitatively affect their
packing in confined spaces. Using analytical theory and numerical simulation we
show that kink formation entails a mixed spool-nematic ordering of
double-stranded DNA or RNA in spherical capsids, consisting of an outer spool
domain and an inner, twisted nematic domain. These findings explain the
experimentally observed nematic domains in viral capsids and imply that
non-linear elasticity must be considered to predict the configurations and
dynamics of double-stranded genomes in viruses, bacterial nucleoids or
gene-delivery vehicles.
