Electrophoretic mobility and deformation of large DNA during gel electrophoresis

We present observations of time-dependent electrophoretic mobility as large DNA molecules are being deformed in agarose gels under an applied electric field by means of movement of fluorescence pattern after photobleaching (MOFPAP). The short-time (\ensuremath{\sim}min) averaged mobility initially increased with increasing electric-field-on time, and finally reached a steady state. We observed a transition behavior in electrophoretic mobility as the ratio of the gel pore size and the DNA size became smaller. Furthermore, an unusual fluctuating fine structure was observed to superimpose on the oscillating pattern of MOFPAP during the initial period when the electric field was turned on.