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. 2007 Nov 2;94(7):2452–2469. doi: 10.1529/biophysj.107.117036

FIGURE 5.

FIGURE 5

B-to-S mode: High-force transition. Simulated force-extension data for a once-nicked 4.5-kbp fragment of λ-phage DNA at 150 mM NaCl, chosen to model experiments reported in the literature (14,15). (a) Effect of pulling rate at 20°C. We employ pulling rates of 3000, 1500, 700, and 150 nm/s. After the B-to-S transition at 65 pN, we observe a strongly rate-dependent unpeeling transition at forces in good agreement with data presented in the literature (14,15). We infer from this comparison that the correct fundamental timescale for our coarse-grained model lies in the 10–100 μs range characteristic of fluorescence correlation spectroscopy data (17,18). We show also the fraction of unpeeled DNA for pulling rates 150 and 1500 nm/s (top panel; arrows and lines correspond to those of force-extension data). (b) Effect of temperature at pulling rate 150 nm/s. We show data for temperatures 0, 30, and 50°C. At sufficiently high temperature, the unpeeling transition preempts the B-to-S conversion, lowering the overstretching plateau.