FIGURE 4.

Probability distributions in m-space for the modified P5ab hairpin. The left column is calculated with a soft spring (λ = 0.01 pN/nm), and the right column with a stiff spring (λ = 0.2 pN/nm). The curves in the top, middle, and bottom rows are calculated for different average extensions 〈R〉 corresponding to the positions indicated by the arrows in Fig. 3 b (first peak, minimum, and second peak in the fluctuation curve, respectively). For the stiff spring, the distribution at the minimum is almost entirely localized on the intermediate state. In contrast, the distribution is spread out over all three states for the soft spring at the same average extension.