Transient orientation of linear DNA molecules during pulsed-field gel electrophoresis.

The transient orientation of lambda DNA and lambda-DNA oligomers has been measured during pulsed field gel electrophoresis. The DNA becomes substantially aligned parallel to the electric field E. In response to a single rectangular pulse, orientation shows an overshoot with a peak at 1 second, then a small undershoot, and finally a plateau. When the field is turned off, the orientation dissipates in two distinct exponential phases. Field inversion leads to periods of orientation with intervening periods of reduced orientation as the chains reverse direction. Field inversion pulses applied to linear oligomers of lambda-DNA show that orientation responses slow down but increase in amplitude as molecular weight increases, for a given field. Because DNA stretching and alignment parallel to E are expected to correlate with DNA velocity, the velocity in response to a pulsed field is also expected to exhibit an overshoot.