Dynamics and thermomechanical stability of DNA in solution

We present an analysis of the response of native DNA solutions to well‐defined elongational flow fields. At low strain rates the DNA duplex behaves as an expanded coil. It shows a noncritical coil‐stretch transition, suggesting relatively little hysteresis of the relaxation time. On the other hand, the relaxation time is consistent with a nonfree draining coil. At higher strain rates we observe midpoint scission. This has been modeled very successfully as a thermomechanically activated process. Scission occurs at hydrolyzable weak linkages along the constituent strands. Complete scission of the DNA helix is, however, considerably less prevalent than would be expected given the low stability of the constituent strands. We speculate upon the molecular origin and biological consequences of this enhanced stability.