Backscattering from a tethered bead as a probe of DNA flexibility

Using an optical tweezer, we trap a DNA polymer tethered bead. Collinear with the tweezer, a red laser light beam probes the bead fluctuations through backscattered radiation measurement. Those fluctuations give information on the flexibility of DNA and can be used to probe the interaction of proteins with DNA. We use this approach to directly monitor the extension of a single DNA polymer beyond its contour length induced by the polymerization of Rec A protein on DNA.