Dresden 2011 – scientific programme

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BP: Fachverband Biologische Physik

BP 15: Single-Molecule Biophysics I

BP 15.4: Talk

Tuesday, March 15, 2011, 11:15–11:30, ZEU 250

Magnetic Torque Tweezers: Probing the torsional properties of DNA, RNA, and DNA filaments — •Jan Lipfert, Gary Skinner, Matthew Wiggin, Jacob Kerssemakers, and Nynke Dekker — Department of Bionanoscience, Delft University of Technology, The Netherlands

The double-stranded nature of DNA links cellular processes such as replication, transcription, and repair to rotational motion and torsional strains. Here we present a novel implementation of magnetic tweezers, magnetic torque tweezers (MTT), that enables the direct measurement of torque [1]. The MTT torque measurement is based on a tracking protocol that monitors x, y, z, and angle and on a redesigned magnet configuration. We have applied the MTT to DNA, RNA, and RecA-DNA heteroduplex filaments. We find the effective torsional stiffness of dsDNA to be significant force-dependent, reconciling previous partially conflicting measurements. Torque measurements on RecA-DNA heteroduplex filaments reveal an initial torsional stiffness about two-fold higher than that of DNA. However, at relatively moderate torques further build-up of torsional strain is prevented by structural transitions in the filament. Preliminary results on the torsional properties of fully double-stranded RNA indicate static properties overall similar to dsDNA, but significantly different dynamics of supercoil formation. Finally, we present a related magnetic tweezers approach that allows straight-forward measurements of free rotation, termed freely-orbiting magnetic tweezers [2]. [1] Lipfert, et al. Nature Methods (2010) [2] Lipfert, Wiggin, et al. Nature Methods, under review