Differences in conformational behavior of ATA and TAT sequences in single strand DNA trimer.

The conformational behavior of single strand (ss) TAT and ATA trimers of DNA have been studied by computational chemistry tools including CICADA software interfaced with AMBER molecular mechanics and dynamics. The Single-Coordinate-Driving (SCD) method has been used in conjunction with molecular dynamics simulated annealing. It has been revealed that the conformational flexibility of each sequence differs substantially from the other one. Four common conformational families have been found for both trimers. These are: helical, reverse-stacked (base 3), half-stacked (base 3), reverse-stacked (base 1). However, the energies of conformers representing the families are different for both the studied systems. An additional conformational family, bulged, has been found for ss(ATA), while ss(TAT) has been found also in half-stacked (base 1) conformation. In general, ss(TAT) exhibits a higher number of low energy conformations while ss(ATA) shows one interesting low energy conformational interconversion between reverse-stacked (A3) family and half-stacked (A3) family. The high conformational variability of the trimers has been confirmed by flexibility analysis and by molecular dynamics simulations, which have also shown the conformational stability of single conformational families. It has been concluded that the methodology used is able to provide a very detailed picture of the conformational space of these molecules.