Stretching and overstretching of DNA in pulsed field gel electrophoresis. II. Coupling of orientation and transport in initial response to the field

The rise of the birefringence following the application of an electric field to DNA in an agarose gel has been quantitatively analyzed to demonstrate the major role played by the chain overstretching. By analyzing the field free decay after short times, we demonstrate that the overshoot is completely due to overstretching. Its time of appearance τ ov varies with the field and DNA length in fair agreement with the E −l N 0 ln N 0 prediction of Lim et al. [ (1990), Journal of Chemical Physics , Vol. 92, pp. 709–721]. The τ ov is also the time corresponding to one tube renewal after relaxation of the overstretching.