Reptation theories of electrophoresis

In this review, we present the main aspects of the reptation theory, which has provided an essential insight into the processes at work during DNA electrophoretic separation in gels. We avoid mathematical developments, and rely as much as possible on an intuitive description. We first present the original biased reptation model, which assumes that the DNA threads its way as a "worm" of fixed length among the fibers of the gel. We then introduce a more recent version, the model of Biased Reptation with Fluctuations (BRF), which allows for longitudinal flexibility along the DNA. We then propose a quantitative comparison with experiments performed in constant field, and discuss the application of reptation theories to pulsed field techniques either with crossed fields or with field inversion. We also discuss at some length the different experiments that led to a criticism of reptation ideas, such as orientation measurements and videomicroscopy. Finally, we use these experiments together with various computer simulations developed recently for gel electrophoresis, to propose a more realistic qualitative description of DNA motion in gels, and we discuss what elements in this motion are relevant to reptation and what processes are not included in present analytical models.