Watching DNA do the twist
30 August 2011 by Webredactie
Researchers from Delft University of Technology and the FOM Foundation have developed a new type of magnetic tweezers to measure changes in the twist of single DNA molecules. This allows a far more accurate observation of DNA-protein interactions, which play a role in copying and repairing DNA for example, than was previously possible. The research, partly funded by a Veni grant awarded to Jan Lipfert, was published yesterday on the website of Nature Communications.
DNA, the molecule in which genetic information at the cellular level is stored, has a double helix structure: two long strands, which are seamlessly joined together by base pairs, twist around each other like a twisted ribbon. When proteins need to bind to the DNA (for example, to read the DNA) the helix is partially unwound. The new instrument, the so-called the freely-orbiting magnetic tweezers, allows the researchers to observe rotational fluctuations of the DNA double helix at the level of single DNA molecules.
In these tweezers, a piece of DNA is attached by one end to a glass surface and by the other to a small magnetic bead (several micrometres in diameter). Unlike conventional magnetic tweezers, the magnetic beads can freely move in a plane perpendicular to the DNA axis. This allows them to rotate around the axis of the DNA, accurately recording any changes in the twist of the tethered DNA molecule. A major strength of this new approach is its simplicity: any conventional magnetic tweezers can be converted into the freely-orbiting magnetic tweezers by simply adjusting the magnetic fields, without the need for any other adjustments in the hardware or software.
The researchers have used the new instrument to precisely measure the stretching force-dependence of the torsional stiffness of DNA. They have also monitored the assembly of RecA ( a DNA-repair protein) on DNA in real time. In the future, the new tweezers will be used to study the interactions of DNA with drugs or molecular motors.
Contact
· Dr Jan Lipfert (Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology), +31 15 278 3552 · Prof. Nynke Dekker (Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology), +31 15 278 3219
Reference
Jan Lipfert*, Matthew Wiggin*, Jacob W.J. Kerssemakers, Francesco Pedaci, and Nynke Dekker (* = equal contribution)
'Freely-Orbiting Magnetic Tweezers to Directly Monitor Changes in the Twist of Nucleic Acids'
Nature Communications (2011)
Image: Protein filament assembly on DNA. Artist’s impression of protein filament assembly on DNA, monitored in the freely-orbiting magnetic tweezers.The tweezers employ a cylindrical magnet (shown in the background). Magnetic beads (shown in light blue) can subsequently rotate freely around the DNA (shown in dark blue and purple) axis. When RecA proteins (transparent yellow) bind to the DNA molecule, the DNA will unwind causing the magnetic bead to rotate with it and execute circular motion. The position of the magnetic bead therefore reports on RecA assembly dynamics in real time.(credit: Tremani/TU Delft)
