HENRY M. SOBELL
Low amplitude breather motions present within a premelton, showing the central beta-structural element alternating between its lowest and highest energy states. These hinge-like motions are coupled with the concerted movement of kink and antikink boundaries on either side.
Isoenergetic breather motions such as these demonstrate the collective effect, an effect well known in many areas of physics. Small movements of atoms in sugar residues within kink and antikink boundaries combine together to give larger movements of atoms in base pairs in the central core region (i.e., 0.025 Angstroms versus 2 to 3 Angstroms). This effect explains how energy is transiently focused into the centers of premeltons to create an "open state" into which drugs and dyes intercalate.
Larger amplitude breather motions give rise to transient breathing distortions that cause (alternate) base pair unstacking, followed by the stretching and the eventual rupture of H-bonds connecting base pairs. These, as well as more complex breather motions, are not shown in this figure.
The molecular structures of premeltons in A- and B- DNA, as well as premeltons connecting A- with B- DNA, have been calculated by nonlinear least squares methods. The results of these studies appear elsewhere in this website.
(Redrawn, from Sobell, H.M. 1985a)