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1.6.2004 [ Search/Archives  | Facts & Figures  | UC Davis Experts  | Seminars/Events  ]

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Natural Nanomachine Caught on Camera

January 16, 2000

Embargoed until 11 a.m. PST Jan. 17.

For the first time, scientists from the University of California, Davis, and the Lawrence Livermore National Laboratory have filmed a molecular machine at work unwinding a DNA double helix.

"This is not only a technical tour de force, but it also reveals behavior of the enzyme that before could only be surmised," said UC Davis molecular biologist Stephen Kowalczykowski, who led the research team. The study will be published in the Jan. 18 issue of the journal Nature.

The scientists studied an enzyme called RecBCD. RecBCD is a helicase, an enzyme that attaches to DNA and moves along the molecule, unwinding the double helix as it goes. This allows other enzymes to access the DNA strands, so that the DNA sequence can be copied or repaired.

To film RecBCD at work, the researchers attached DNA molecules labeled with a fluorescent dye to polystyrene beads one-millionth of a meter in size. Under the microscope, the bead looks like a white sphere with a bright string of DNA attached.

They let RecBCD attach to the free end of the DNA strand, and used laser beams as "optical tweezers" to move the beads into position under a microscope. To start the enzyme, they added ATP, a chemical fuel that powers many enzymes.

As RecBCD unwound the DNA strands, the fluorescent dye was removed, so the bright string of DNA seemed to get shorter.

"The enzyme unwinds DNA in a process that is continuous from start to finish, with no detectable pausing," said Kowalczykowski. New data from the study could take months or even years to fully understand, he said.

Note for editors: A movie of RecBCD at work is available. It will be posted as supplemental data on the Nature Web site <http://www.nature.com>, or contact Andy Fell for details.

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