Abstract
The dynamics of polymer translocation through a pore has been the subject ofrecent theoretical and experimental works. We have considered theoreticalestimates and performed computer simulations to understand the mechanism ofDNA uptake into the cell nucleus, a phenomenon experimentally investigated byattaching a small bead to the free end of the double helix and pulling this beadwith the help of an optical trap. The experiments show that the uptake ismonotonic and slows down when the remaining DNA segment becomes very short.Numerical and analytical studies of the entropic repulsion between theDNA filament and the membrane wall suggest a new interpretation ofthe experimental observations. Our results indicate that the repulsionmonotonically decreases as the uptake progresses. Thus, the DNA is pulled ineither (i) by a small force of unknown origin, and then the slowing downcan be interpreted only statistically, or (ii) by a strong but slow ratchetmechanism, which would naturally explain the observed monotonicity, butthen the slowing down requires additional explanations. Only furtherexperiments can unambiguously distinguish between these two mechanisms.
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