Figure 1.

Interaction of QDot-labeled EcoRV with tweezers-manipulated DNA. (A) Scheme of the setup: a DNA molecule is extended between two beads held by double optical traps, respectively. In addition, one of the beads is attached to the surface via a second DNA molecule. Enzymes sliding along the DNA are detected by the fluorescence emission of a QDot. (B) Overlaid bright field and fluorescence image of the two trapped beads and two successive sliding events of QDot-labeled enzymes on the extended DNA (129 nm/pixel). (C) Trajectories from the two interaction events recorded in B in X (direction of DNA extension) and Y direction. Gaps in the trajectories are caused by fluorescence intermittency. (D) MSD curves calculated from the interaction events in B depend linearly on time at short times in X direction, which demonstrates the sliding of the enzymes along the DNA. Nonlinear deviation at longer timescales can be explained by the stochastic nature of the linear diffusion (compare Fig. 2).