Figure 1.

Observation system (not to scale). A single dsDNA was attached to a glass surface at one end and to a doublet bead, which served as a marker of rotation, at the other end. Each end of the DNA had three tags of biotin or digoxigenin, preventing the DNA from free rotations. Since the images of beads on a CCD agreed with the top view, unwinding or rewinding the right-handed helical structure of a double-stranded DNA causes clockwise or counterclockwise revolution of the bead image, respectively.