Figure 1.

Generation of three different DNA conformations. (A) (top) DNA with biotins at one or both ends are introduced into a streptavidin-coated flow cell at a constant flow rate. (bottom) During the flow, DNA binds to the surface at one end and becomes stretched in the direction of the flow. If biotin is present at the distal end, then the DNA forms an extended double tether, otherwise it remains singly tethered. (B) Upon addition of SxO, doubly-tethered intact DNA becomes supercoiled. (C) Nicked DNA remains torsionally relaxed. (D) Singly-tethered DNA is torsionally relaxed. Upon application of flow, the molecules from (B) to (D) assume readily identifiable shapes.