  We present a numerical study of the effect of knotting on the ejection of
flexible and semiflexible polymers from a spherical, virus-like 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.
