Conformations of deoxydinucleoside phosphates containing pyrimidine-pyrimidine photodimers.

Conformational analysis of deoxydinucleoside monophosphates with the sequences TpT and CpC have been carried out with the incorporation of both cyclobutane type pyrimidine dimers and 6-4 photoadducts using the methods of molecular mechanics energy minimization. The effect of flexibility with respect to sugar geometries and glycosidic torsions have been studied and the relative energies of a large variety of structures have been compared. The salient features obtained from these calculations have been compared with the crystallographic and spectroscopic data on pyrimidine dimer incorporated deoxydinucleoside monophosphates. Effects of "inserting" the energetically favourable conformations of such structures into B-DNA helices have been discussed in terms of the distortions in helical structures.