title: Simple horizontal magnetic tweezers for micromanipulation of single DNA molecules and DNA-protein complexes.
abstract: We report the development of a simple-to-implement magnetic force transducer that can apply a wide range of piconewton (pN) scale forces on single DNA molecules and DNA-protein complexes in the horizontal plane. The resulting low-noise force-extension data enable very high-resolution detection of changes in the DNA tether's extension: ~0.05 pN in force and <10 nm change in extension. We have also verified that we can manipulate DNA in near equilibrium conditions through the wide range of forces by ramping the force from low to high and back again, and observing minimal hysteresis in the molecule's force response. Using a calibration technique based on Stokes' drag law, we have confirmed our force measurements from DNA force-extension experiments obtained using the fluctuation-dissipation theorem applied to transverse fluctuations of the magnetic microsphere. We present data on the force-distance characteristics of a DNA molecule complexed with histones. The results illustrate how the tweezers can be used to study DNA binding proteins at the single molecule level.
authors.affiliation: Department of Physics, The Catholic University of America, Washington, DC.|Vitreous State Laboratory, Washington, DC.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: McAndrew
authors.affiliation: Vitreous State Laboratory, Washington, DC.|Department of Biomedical Engineering, The Catholic University of America, Washington, DC.
authors.forename: Christopher
authors.initials: C
authors.lastname: Tyson
authors.affiliation: Carnegie Mellon University, Pittsburgh, PA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Zischkau
authors.affiliation: Vitreous State Laboratory, Washington, DC.
authors.forename: Patrick
authors.initials: P
authors.lastname: Mehl
authors.affiliation: Department of Biology, The Catholic University of America, Washington, DC.
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Tuma
authors.affiliation: Department of Physics, The Catholic University of America, Washington, DC.|Vitreous State Laboratory, Washington, DC.
authors.forename: Ian L
authors.initials: IL
authors.lastname: Pegg
authors.affiliation: Department of Physics, The Catholic University of America, Washington, DC.|Vitreous State Laboratory, Washington, DC.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Sarkar
mesh_terms: D004247:DNA / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry*; D008280:Magnetics; D008846:Micromanipulation / Q000379:methods*; D008863:Microspheres; D036103:Nanotechnology
chemical_list: D046911:Macromolecular Substances; D004247:DNA
keywords: differential measurement; magnetic trap; magnetic tweezers; single molecule–micromanipulation