Magnetic Tweezers

Abstract Magnetic tweezers is a technique that allows applying a constant pulling force and torque on a nucleic acid molecule while measuring its elongation in real time. By means of two magnets, the polymer is stretched and twisted between a magnetic bead and the surface of a glass cover slide. In the course of an experiment, the position of the magnetic bead is followed in real time while a buffer containing proteins, adenosine triphosphate (ATP), etc. is introduced in the experiment chamber. This approach has been used to study deoxyribonucleic acid (DNA) condensation, mechanical properties of nucleic acids and dynamics of protein–DNA interactions. In this article an introduction to the Magnetic Tweezers technique is given and some examples of application presented. Key Concepts: Magnetic Tweezers allow stretching and twisting nucleic acids (NA) using magnetic microspheres and a magnetic field. An NA is attached at one end to a magnetic bead and at the other end to a transparent glass surface. The position of the bead is determined from the optical image given by a video camera. The force acting on the NA is calculated from the movements of the tethered magnetic bead. Magnetic Tweezers are used to study mechanical properties of NA and real‐time dynamics of protein–DNA interactions.