Static and dynamic conformational properties of AT sequences in B-DNA.

A theoretical study of the optimal conformations of nucleic acid oligomers containing tracts of AT base pairs is presented. The oligomers are studied in isolation and complexed with netropsin, a minor groove binding ligand. The flexibility of the oligomers and of their complexes is calculated by adiabatic mapping with respect to the total winding angle. The results of this study show that in uncomplexed oligomers the dinucleotide junctions AA, AT and TA have very different structural parameters and different responses to winding stress. The TA junction is clearly the most flexible and is the principal site for accommodating the imposed overwinding. Complexation by netropsin leads to two important effects: firstly, the three junctions adopt more uniform structures, the largest changes again being observed for TA, secondly, the differences in flexibility as a function of sequence are strongly attenuated.