Figure 6.

(A) Fluorescence images taken from a sequence recorded during the extension and relaxation of the DNA-YO complex in the presence of 100 nM YO (pulling speed = 1 μm/s, scale bar = 5 μm). (B) Total fluorescence intensity plotted as a function of force (black squares, extension; gray squares, relaxation). (C) Kymograph created from the sequence of images recorded simultaneously while carrying out force spectroscopy, where the horizontal axis represents time, and the vertical axis is extension. The two bright lines in the kymograph represent the streptavidin-coated polystyrene beads at either end of the DNA molecule. The force exerted on the complex is plotted as a function of time in the plot below the kymograph.