THEORY OF DNA ELECTROPHORESIS IN PHYSICAL GELS AND ENTANGLED POLYMER-SOLUTIONS

A scaling theory is presented for the electrophoretic mobility of DNA in sieving media that form dynamically evolving meshworks, such as phy sical gels and solutions of entangled polymers. In such media, the top ological constraints on the DNA's motion are perpetually changing as c ross links break and rejoin or as the polymers diffuse. It is shown th at if the rate of constraint release falls within a certain range (whi ch depends on the field strength), fractionation can be extended to hi gher molecular weights than would be feasible using a permanent gel of equivalent pore size. This improvement is a consequence of the disrup tive effect that constraint release has on the mechanism of molecular orientation. Numerical simulations support the predictions of the theo ry. The possibility of realizing such a system in practice, with the a im of improving on current electrophoresis methods, is commented upon. It is suggested that semidilute polymer solutions may be a versatile medium for the rapid separation of long single-stranded DNA molecules, and the particular quality of solution required is identified.