DNA overwinds when stretched

When DNA is gently stretched, it appears to wind itself more tightly, a counterintuitive finding that may eventually help explain how proteins bind to DNA, researchers reported this week in Nature."This is a very intellectually interesting result that is very fundamental to understanding the properties of DNA," Wilma Olson at Rutgers University in Piscataway, N.J., not a coauthor, told The Scientist.Scientists have studied DNA's mechanical properties on a single molecular level for more than a decade. A previous study did not see DNA unwinding when gently stretched, but relatively noisy data may have obscured the miniscule effect, according to the authors of the latest paper, led by Carlos Bustamante at the University of California at Berkeley.To stretch the DNA, Bustamante and his team attached a magnetic bead to one end of a DNA molecule and attached the other end of the DNA molecule to glass, then pulled the...