Tying a Knot in DNA




A single DNA molecule of length 16 μm was knotted with optical tweezers.  First, the ends of the DNA were attached to two polystyrene beads held in optical traps, by moving the microscope stage.  Then the upper bead was manipulated with the optical tweezers.  Unlike actin filaments, knotted DNA did not break upon pulling, suggesting the possibility of using it as a micromanipulation tool.  Indeed, the DNA in this movie was tied around many unstained actin filaments suspended in the medium, forcing them to form a tight bundle inside the knot.  Note that the knot position does not change upon loosening, indicating that the knot was made around entangled actin filaments.
                                                               Arai, Y. et al., Nature 399, 466-468 (1999).