Conformations of dinucleoside monophosphates in relation to duplex DNA structures.

Mononucleotide conformations are important in understanding the structural aspects of nucleic acids and polynucleotides. In order to study the influence of stacking interactions between adjacent bases in a polynucleotide on the preferred conformations of mononucleotides, conformational energy calculations have been carried out on dinucleoside monophosphate fragments. Four base sequences-d(ApT), d(TpA), d(CpG), and d(GpC)have been analyzed in the framework of helical structures. Flexibility of the furanose ring has been incorporated in the investigations. Energetically favored conformers of the four compounds correspond to a variety of leftand right-handed uniform helical structures, similar to those of the commonly observed polymorphous forms. Implications of these investigations on the further understanding of doublehelical polynucleotide conformations are briefly discussed.