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Title  : "LASER TWEEZER" TECHNIQUE MEASURES DNA "MECHANICS"
Type   : Press Release
NSF Org: OD / LPA
Date   : February 6, 1996
File   : pr966



Cheryl Dybas                                February 8, 1996
(703) 306-1070                                   NSF PR 96-6

                    "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.
                            -end-



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