4-STRANDED DNA HELICES - CONFORMATIONAL-ANALYSIS OF REGULAR POLY(DT).POLY(DA).POLY(DA).POLY(DT) HELICES WITH VARIOUS TYPES OF BASE BINDING

The paper presents results obtained in conformational analysis of homopolymeric four-stranded poly(dT).poly(dA).poly(dA).poly(dT)DNA helices in which the pairs of strands with identical bases are parallel and have a two-fold symmetry axis. All possible models of base binding to yield a symmetric complex have been considered. The dihedral angles of sugar-phosphate backbones and helix parameters, which are consistent with the minima of conformational energy for four-stranded DNAs, have been determined using the results of optimization of conformational energy calculated at atom-atom approximation. Potential energy is shown to depend on the structure of base complexes and on the mutual orientation of unlike strands. Possible biological functions of four-stranded helices are discussed.