Figure 1

Double strand response to torsion and tension:

(a), “Hat-curves” show the mean relative extension of a 600-bp duplex against superhelical density σ for various applied forces F. Error bars indicate thermal fluctuations in the end-to-end distance, rather than sampling uncertainties. (b), Mean fraction of plectonemes, bubbles and tip-bubble plectonemes, as a function of force for σ = −0.08. Inset: Fluctuations (standard deviation σ_L) of end-to-end distances as a function of force for σ = −0.08 show two maxima, the first at the point when tip bubbles form in plectonemes, the second at the transition from tip-bubble plectonemes to bubbles only. Results for L = 1500 bp as well as for other values of σ can be found in Supplementary Material (SM) Sections III and VII. (c), State diagram of structures. Tip-bubble regions indicate points with at least a 40% probability of a plectoneme with a tip bubble.