FIG. 2.

Hopping between the SS and CS near the supercoiling transition, for the same conditions as Fig. 1. As linking number K is slowly increased near K*, thermal fluctuations induce hopping between states with (CS) and without (SS) a plectoneme. Averaging over these two states gives a direct way of measuring the torque jump: we first separate the data into SS (black) and CS (red) by setting a threshold for the extension, and then average each set of data near the transition, producing the black and red bars on the right side of the figure. Using multiple traces gives an average torque jump of Δτ = 2.93 ± 0.68 pN nm for L = 2.2 kbp at F = 2 pN.