Knot-controlled ejection of a polymer from a virus capsid.

We present a numerical study of the effect of knotting on the ejection of flexible and semiflexible polymers from a spherical, viruslike capsid. The polymer ejection rate is primarily controlled by the knot, which moves to the hole in the capsid and then acts as a ratchet. Polymers with more complex knots eject more slowly and, for large knots, the knot type, and not the flexibility of the polymer, determines the rate of ejection. We discuss the relation of our results to the ejection of DNA from viral capsids and conjecture that this process has the biological advantage of unknotting the DNA before it enters a cell.