LIFESCIENCE: Tying a molecular knot with optical tweezers

[Eduardo Kac <ekac@artic.edu>]

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ARS ELECTRONICA FESTIVAL 99
LIFESCIENCE
Linz, Austria, September 04 - 09
http://www.aec.at/lifescience
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Nature 399, 446 - 448 (1999) © Macmillan Publishers Ltd.
3 June 1999 (Vol. 399 No 6735)


Tying a molecular knot with optical tweezers

YASUHARU ARAI, RYOHEI YASUDA, KEN-ICHIROU AKASHI,
YOSHIE HARADA, HIDETAKE MIYATA,
KAZUHIKO KINOSITA JR & HIROYASU ITOH

Filamentous structures are abundant in cells. Relatively
rigid filaments, such as microtubules and actin, serve as
intracellular scaffolds that support movement and force,
and their mechanical properties are crucial to their function
in the cell. Some aspects of the behaviour of DNA,
meanwhile, depend critically on its flexibility--for example,
DNA-binding proteins can induce sharp bends in the helix.
The mechanical characterization of such filaments has
generally been conducted without controlling the filament
shape, by the observation of thermal motions or of the
response to external forces or flows. Controlled buckling
of a microtubule has been reported, but the analysis of the
buckled shape was complicated. Here we report the
continuous control of the radius of curvature of a
molecular strand by tying a knot in it, using optical
tweezers to manipulate the strand's ends. We find that actin
filaments break at the knot when the knot diameter falls
below 0.4 µm. The pulling force at breakage is around
1 pN, two orders of magnitude smaller than the tensile
stress of a straight filament. The flexural rigidity of the
filament remained unchanged down to this diameter. We
have also knotted a single DNA molecule, opening up the
possibility of studying curvature-dependent interactions
with associated proteins. We find that the knotted DNA is
stronger than actin.



       Nature © Macmillan Publishers Ltd 1999

______________________________________________________________________

Eduardo Kac
Assistant Professor of Art and Technology
Art and Technology Department
The School of the Art Institute of Chicago
112 S. Michigan Avenue, Room 414
Chicago IL 60603
Phone: (312) 345-3567
Fax: (312) 345-3565
E-mail: ekac@artic.edu

http://www.ekac.org

______________________________________________________________________

Research Fellow
Centre for Advanced Inquiry in the Interactive Arts,
University of Wales, Newport, UK
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