Figure 6.

Salt dependence of the buckling transition parameters at 3.5 pN for the 1.9 kbp DNA molecule. Experimental values are shown as circles. Predictions from the initial-loop model are shown as black lines. (A) Jump size at buckling equilibrium. (B) Position of the buckling equilibrium. (C) Change of twist transferred into writhe during buckling $\Delta N_{\text{b}}^{\text{p}}$ at the buckling equilibrium and corresponding torque change ΔΓ_b. (D) Superhelix-formation energy E₂, inferred postbuckling torque (solid circles and solid line), and initial-loop formation energy E₁ (open circles and dashed line). (Inset) Energy difference between E₁ and E₂.