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Science 20 January 1995:
Vol. 267. no. 5196, pp. 378 - 380
DOI: 10.1126/science.7824935
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Articles

Science, Vol 267, Issue 5196, 378-380
Copyright © 1995 by American Association for the Advancement of Science

articles

Measurement of lactose repressor-mediated loop formation and breakdown in single DNA molecules

L Finzi and J Gelles

Graduate Department of Biochemistry, Brandeis University, Waltham, MA 02254.

In gene regulatory systems in which proteins bind to multiple sites on a DNA molecule, the characterization of chemical mechanisms and single-step reaction rates is difficult because many chemical species may exist simultaneously in a molecular ensemble. This problem was circumvented by detecting DNA looping by the lactose repressor protein of Escherichia coli in single DNA molecules. The looping was detected by monitoring the nanometer-scale Brownian motion of microscopic particles linked to the ends of individual DNA molecules. This allowed the determination of the rates of formation and breakdown of a protein-mediated DNA loop in vitro. The measurements reveal that mechanical strain stored in the loop does not substantially accelerate loop breakdown, and the measurements also show that subunit dissociation of tetrameric repressor is not the predominant loop breakdown pathway.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Direct demonstration and quantification of long-range DNA looping by the {lambda} bacteriophage repressor.
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See me, feel me: methods to concurrently visualize and manipulate single DNA molecules and associated proteins.
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Single-molecule manipulation reveals supercoiling-dependent modulation of lac repressor-mediated DNA looping.
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Dynamics and consequences of DNA looping by the FokI restriction endonuclease.
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Lac repressor hinge flexibility and DNA looping: single molecule kinetics by tethered particle motion.
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Real-time observation of DNA looping dynamics of Type IIE restriction enzymes NaeI and NarI.
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Supercoiling and denaturation in Gal repressor/heat unstable nucleoid protein (HU)-mediated DNA looping.
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Concentration fluctuations in a mesoscopic oscillating chemical reaction system.
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Nonequilibrium mechanism of transcription termination from observations of single RNA polymerase molecules.
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Twist and shout (and pull): Molecular chiropractors undo DNA.
J. F. Marko (1997)
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Statistical Kinetics of Processive Enzymes.
M.J. Schnitzer and S.M. Block (1995)
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Compaction of single DNA molecules induced by binding of integration host factor (IHF).
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