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.
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