STRETCHING AND OVERSTRETCHING OF DNA IN PULSED-FIELD GEL-ELECTROPHORESIS .2. 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 de monstrate the major role played by the chain overstretching. By analyz ing the field free decay after short times, we demonstrate that the ov ershoot is completely due to overstretching. Its time of appearance ta u(ov) varies with the field and DNA length in fair agreement with the E-1N0ln N0 prediction of Lim et al. [(1990), Journal of Chemical Physi cs, Vol. 92, pp. 709-721]. The tau(ov) is also the time corresponding to one tube renewal after relaxation of the overstretching. (C) 1993 J ohn Wiley & Sons, Inc.