NSF PR 96-6 - February 8, 1996
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Laser Tweezer Technique Measures DNA Mechanics
The enormous amount of DNA required to define the
structure, and hence function, of higher organisms
means that nature has had to develop special DNA packaging
techniques. In order for the DNA to be used, selective
unfolding of it is required, but how strongly does
the molecule resist this bending and stretching?
In the February 9th issue of the journal Science,
National Science Foundation (NSF)-funded scientist
Carlos Bustamante of the Institute of Molecular Biology
at the University of Oregon, reports on results of
a novel measurement of the "mechanical" properties
of DNA. The measurement involves essentially "gripping"
the DNA at both ends, pulling, and determining the
DNA's resistance to stretching.
Bustamante's experiment involved fixing small polystyrene
beads to each end of a DNA molecule to provide "handles."
Next, a tiny but accurately measured force was applied
to one bead while the other bead remained still. Using
a highly controlled laser beam, this "laser tweezer"
technique permitted the measurement of the elastic
behavior of the DNA molecule over a wide range of
pulling forces.
An interesting observation was that at some pulling
forces, the DNA molecule abruptly shifts to a new
structure with a distinctly different resistance.
Bustamante suspects that this "structural transition"
has important consequences for the interactions of
DNA with so-called DNA-binding proteins. These observations
contribute to development of a picture of the interactions
occurring in a cell's nucleus, and reveal the physical
processes involved in molecular recognition, says
Kamal Shukla of NSF's division of molecular and cellular
biosciences, which supported Bustamante's research.
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