Figure 6.

Constant force measurements at a linking number density σ_tot = −0.03. Three different forces are shown (top to bottom): 0.84, 0.74, and 0.65 pN. (Red) The 20 points of median filtered data, emphasizing the discrete transitions in extension. Histograms of the extension are shown on the right side of the time traces (black and red bars). The calculated extension distribution is superimposed on the histogram (solid black lines). The discrete levels are attributed to ∼400 bps of plectonemic DNA transferring back and forth into 380-bps twisted and 20-bps melted DNA. To see this figure in color, go online.