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Mechanically controlled DNA extrusion from a palindromic sequence by single molecule micromanipulation.
[Phys. Rev. Lett. 96 (18):188102 (2006)]
Alexandre Dawid, Fabien Guillemot, Camille Breme, Vincent Croquette, François HeslotA magnetic tweezers setup is used to control both the stretching force and the relative linking number DeltaLk of a palindromic DNA molecule. We show here, in absence of divalent ions, that twisting negatively the molecule while stretching it at approximately 1 pN induces the formation of a cruciform DNA structure. Furthermore, once the cruciform DNA structure is formed, the extrusion of several kilo-base pairs of palindromic DNA sequence is directly and reversibly controlled by varying DeltaLk. Indeed the branch point behaves as a nanomechanical gear that links rotation with translation, a feature related to the helicity of DNA. We obtain experimentally a very good linear relationship between the extension of the molecule and DeltaLk. We use then this experiment to obtain a precise measurement of the pitch of B-DNA in solution : 3.61 +/- 0.03 nm/turn.
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