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. 2014 Jul 24;42(14):8996–9004. doi: 10.1093/nar/gku635

Figure 1.

Figure 1.

Characterization of the equilibrium binding constant and the cooperativity parameter using optical tweezers. (A) Schematic of optical tweezers. Phage-λ DNA (not to scale) is captured between two beads held on one side by two focused laser beams and on the other side by a micropipette. The DNA is stretched by moving the micropipette and measuring the resulting force with the optical tweezers. (B) The force-extension curve is obtained by stretching the DNA in the absence (black line) and in the presence of 1 nM HMO1 (orange line). The change in overstretching force in the presence of HMO1 proteins is indicated by ΔFov (C) To study the change in mechanical properties of the DNA in the presence of HMO1, data points (open symbols) in the presence (orange) and absence (black) of HMO1 are fit using the extensible WLC model (Equation 1, solid lines). (D) The persistence length versus concentration (symbols) is fit (dotted line) to Equation (4). (E) The contour length versus concentration (symbols) is fit (dotted line) to Equation (5). (F) The overstretching force versus concentration (symbols) is fit (dotted line) to Equation (6). The error bars indicate standard error of measurement for N ≥4 for all panels.