DNA Translocation by RecBCD Helicase/Nuclease
This movie shows an experiment from
Chi-sequence Recognition and DNA Translocation by Single RecBCD
Helicase/Nuclease Molecules.
Kathleen M. Dohoney and Jeff Gelles
(2001) Nature 409, pp. 370 - 374. [abstract]
[full
text*]
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The movie shows a bead-labeled RecBCD molecule translocating along a single DNA molecule. Initially, the free diffusion of beads in solution is seen. After a few seconds, one of the bead-labeled enzyme molecules attaches to the end of a DNA molecule at the center of the field (arrows); attachment is detected as the cessation of free diffusion and the commencement of characteristic tethered-particle Brownian motion in the vicinity of a single point on the microscope slide. Subsequent translocation of the enzyme along the DNA molecule is visualized as a gradual decrease in the spatial range of the Brownian motion; this decrease continues until the beads ceases visible movement altogether. This experiment was performed as shown in Fig. 1 of the paper, except that the ATP concentration was reduced to 10 µM to slow translocation. The video is real time; the frame size is 6.5 µm wide by 6.6 µm tall.