Gel electrophoretic mobility of single-stranded DNA: The two reptation field-dependent factors

The reptation model is the dominant theory in understanding the electrophor etic separation of single-stranded DNA molecules in gels or entangled polym er solutions. Recently, we showed that the Ogston and reptation regimes are separated by an entropic trapping regime at low field intensities. Here, w e report the first comparison of the field-dependent part of the DNA mobili ty for both small and long reptating molecules. We show that both mobilitie s increase linearly with field intensity, with the mobility of the longer ( comigrating) fragments increasing faster than that of the smaller ones. We compare our results to the predictions of the biased reptation model.