The helical repeat of DNA at high temperature.

The increasing number of studies on thermophilic organisms addressed the question of DNA double helix parameters at high temperature. The present study shows that the helix rotation angle per base pair omega of an unconstrained DNA decreases linearly upon temperature increase, up to the premelting range. In the ionic conditions tested, this rule extends to temperatures up to 85 degrees C, which is a common growth temperature for many hyperthermophilic organisms. In addition, the torsional constant K of DNA decreases with temperature, indicating that the energy required to modify the DNA twist is lower at high temperature. These findings have several implications for people working on the structure and enzymology of DNA at high temperature.