(a) Schematic of the equilibrium experiment. A magnetic bead attached to the DNA molecule at the left end is rotated with a mean torque 〈τ〉, and the molecule is attached to a substrate at the right end to fix the twist. (b) Schematic of the nonequilibrium experiment. A magnetic bead attached to DNA at the left end is rotated at a constant angular velocity, ω0, and the molecule is nicked so that it releases twist. Twist release is opposed by the viscous drag, ζB, of the “rotorbead,” which is attached to DNA to the left of the nick.