Mechanically controlled DNA extrusion from a palindromic sequence by single molecule micromanipulation.
A 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.
Dawid
Alexandre
A
Laboratoire Pierre Aigrain, Unité Mixte de Recherche 8551, Ecole Normale Supérieure, 24 Rue Lhomond, 75005 Paris, France.
Guillemot
Fabien
F
Brème
Camille
C
Croquette
Vincent
V
Heslot
François
F
D001696:Biomechanical Phenomena; D004278:DNA, Superhelical / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008846:Micromanipulation; D009690:Nucleic Acid Conformation
D004278:DNA, Superhelical; D007477:Ions