Effect of the electric field on the apparent mobility of large DNA fragments in agarose gels

Abstract The electrophoresis of a series of DNA fragments ranging in size from 0.5 to 12 kilobase pairs, has been studied as a function of agarose gel concentration and electric field strength. The apparent mobility of all fragments decreased with decreasing electric field strength and with increasing gel concentration. When extrapolated to zero electric field strength and zero agarose concentration, the apparent mobility of all DNA fragments extrapolated to a common value (2.0 ± 0.1) × 10 −4 cm 2 /V s. The square roots of the retardation coefficients of the various fragments were found to be linearly related to the root‐mean‐square radii of gyration of the fragments, as predicted by pore‐size distribution theory. As predicted by reptation theory, the molecular weights of the various fragments were found to be linearly related to the reciprocal of the apparent mobilities. An equation is given for estimating the apparent pore size of agarose gels between 0.25 and 1.5% in concentration.