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Magnetic Tweezers Measurement of Single Molecule Torque

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posted on 08.04.2009, 00:00 by Alfredo Celedon, Ilana M. Nodelman, Bridget Wildt, Rohit Dewan, Peter Searson, Denis Wirtz, Gregory D. Bowman, Sean X. Sun
Torsional stress in linear biopolymers such as DNA and chromatin has important consequences for nanoscale biological processes. We have developed a new method to directly measure torque on single molecules. Using a cylindrical magnet, we manipulate a novel probe consisting of a nanorod with a 0.1 μm ferromagnetic segment coupled to a magnetic bead. We achieve controlled introduction of turns into the molecule and precise measurement of torque and molecule extension as a function of the number of turns at low pulling force. We show torque measurement of single DNA molecules and demonstrate for the first time measurements of single chromatin fibers.