On the compact form of linear duplex DNA: globular states of the uniform elastic (persistent) macromolecule

A theory of collapse of DNA considered as unifilar homopolymer is suggested. The collapse is interpreted as the coil-globule transition. Three reasons of the collapse such as the confinement in a microcavity, the influence of poor low-molecular-weight solvent and the influence of polymeric solvent were studied. The results are summed up by the stage diagrams in variables: DNA length versus the characteristics of the compaction factor (the cavity volume, the energy of attraction of DNA segments in poor low-molecular-weight solvent and the concentration of polymer added). It is shown that a sufficiently long DNA forms the spherical compact particle while the relatively short DNA forms the toroidal one. More delicate features of the tertiary structure are determined by the relative role of the bending stiffness and steric repulsions in preventing further collapse. As the compaction occurs in polymeric solvent almost all added polymer is forced out from the globule. Thus, the internal structure of the compact DNA particle in polymeric solvent is similar to that in the model of microcavity.