FIG. 1.

Extension and torque as a function of linking number K, for L = 2.2 kbp at F = 2 pN. Black lines show data from Ref. [1], smoothed using a “boxcar” average of nearby points, with window size 1/4 turn for the extension data and 4 turns for the torque data. The light blue lines show worm-like chain (WLC) predictions below the transition [in the unsupercoiled “stretched” state (SS)], and fits to the data after the transition [in the “coexisting” state (CS) with both plectonemic and stretched DNA], linear for the extension and constant for the torque. The size of the torque jump, not directly visible in the smoothed data, is implied by the torque for the WLC, the CS fit, and the transition linking number K* in the extension data. Inset: Simulated DNA showing the CS of a plectoneme and straight DNA, ignoring thermal fluctuations. The ends of the DNA are held with fixed orientation and pulled with a constant force F, here 2 pN.