Effect of nonparallel alternating fields on the mobility of DNA in the biased reptation model of gel electrophoresis

Chromosome-size DNA molecules can now be separated using a variety of pulsed field gel electrophoresis techniques. In this article, we study the predictions of the biased reptation model concerning the effect of two pulsed fields, making an arbitrary angle, on the power of separation of gel electrophoresis. Separation is predicted to be largely enhanced for obtuse angles, in agreement with experiments. Interestingly, very large molecules, which are not separated by pulsed fields, are predicted not to migrate along the gel diagonal for fairly long periods of time. Finally, we discuss the optimization of these techniques using the results of the theory, and the limitations of the latter when fluctuations and intramolecular modes probably dominate the system.