Driven polymer translocation through a narrow pore

Motivated by experiments in which a polynucleotide is driven through a prot einaceous pore by an electric field, we study the diffusive motion of a pol ymer threaded through a narrow channel with which it may have strong intera ctions. We show that there is a range of polymer lengths in which the syste m is approximately translationally invariant, and we develop a coarse-grain ed description of this regime. From this description, general features of t he distribution of times for the polymer to pass through the pore may be de duced. We also introduce a more microscopic model. This model provides a ph ysically reasonable scenario in which, as in experiments, the polymer's spe ed depends sensitively on its chemical composition, and even on its orienta tion in the channel. Finally, we point out that the experimental distributi on of times for the polymer to pass through the pore is much broader than e xpected from simple estimates, and speculate on why this might be.