Extended Data Fig. 7: Water flow-induced rotation of a DNA molecule.

a, Simulation system containing a 21 bp DNA helix (light grey; green backbone) submerged in a volume of 1 M KCl electrolyte (semi-transparent molecular surface); only a fraction of ions is shown explicitly, for clarity. The DNA molecule is made effectively infinite by connecting each of its strands to itself over the periodic boundary of the simulation unit cell. For illustration, partial periodic images of the DNA molecule are shown in grey. The water flow is produced by applying a small, constant force to each water molecule parallel to the axis of the DNA molecule (see Methods). Phosphorus atoms of the DNA are harmonically restrained to the surface of a cylinder such that the DNA is free to rotate about its axis; additional restrains prevent the molecules from drifting in the direction of the flow. b, Angular displacement of the DNA molecule as a function of simulation time. The sign of displacement is prescribed by the right-hand rule with respect to the positive direction of the force applied to the water molecules, as indicated in panel a. c, Average angular velocity of the DNA helix versus pressure gradient due to force applied to each water molecule. Each data point was determined by averaging a ~60–200 ns MD trajectory. The line shows a linear regression fit to the data. The right axis displays the rotational velocity of the DNA in units of revolutions per minute (RPM).