Figure 7. Impact of intercalators on DNA overstretching and DNA-enzyme activity.

(a–c) Kymographs and corresponding force-extension curves (red) in the presence of YOYO (a), SbG (b) and YO (c) at 100 mM NaCl. The kymograph image and corresponding force-extension curves are co-aligned along the horizontal axis, which is possible because of the constant stretching speed of the moving bead (visible as the bright, upward tilted bar in the image). Thus, the fluorescence pattern in the vertical direction in the kymograph is a DNA-staining pattern at the DNA extension indicated on the horizontal axis. Cyan curves, no intercalator present. (d) Time traces recorded at 40 pN showing dsDNA digestion by the exonuclease activity of T7 DNA polymerase. Black, no intercalator; red, YO; blue, SxO; green, SbG. Under these experimental conditions, YOYO abolished all exonuclease activities. (e) Histograms of the resulting average digestion rates obtained at the four different conditions (Methods).