Configurational statistics of polynucleotide chains. A single virtual bond treatment.

A simplified single virtual bond scheme has been developed for the calculation of mean-square unperturbed dimensions in polynucleotide chains. As a consequence of the structural rigidity of the sugar residues in the chain, it is possible to represent the six chemical bonds comprising the chain backbone repeating unit by a single virtual bond (connecting successive phosphorus atoms). The mutual orientation of a pair of adjoining virtual bonds is determined by the angles of rotation about the phosphodiester bonds adjoining intervening phosphorus atoms and is independent of the orientation of all other virtual bonds in the chain. Computed values of chain dimensions based on the single virtual bond scheme are comparable to those calculated previously using a two virtual bond model which permits rotational flexibility in the sugar moieties of the chain.