Laser Ties Knots in DNA Strands

TOKYO, Japan, June 3 -- A Japanese researcher has used a laser to tie knots in strands of DNA. Yasuharu Arai, a graduate student at Keio University in Yokohama, used a microscope equipped with optical tweezers to twist the molecular strings. He first attached handles to each end of the strand of DNA, then directed the laser at the handles, which by their nature were drawn toward light. With one beam holding an end of the strand in place, he used the second beam to loop the other end of the strand into a knot.
After months of failure, Arai has succeeded in knotting more than a dozen strands of DNA from a fish-infecting virus. He even managed to put two knots in a few strands. We did it for fun and for the challenge, just like climbing Mount Everest for the first time, said Kazuhiko Kinosita Jr., a physics professor who helped coordinate the projects. No one had done it before. Scientists hope the technique may help in cell research.