Abstract
We show that minuscule entropic forces, on the order of 100 fN, can prevent the formation of DNA loops—a ubiquitous means of regulating the expression of genes. We observe a tenfold decrease in the rate of LacI-mediated DNA loop formation when a tension of 200 fN is applied to the substrate DNA, biasing the thermal fluctuations that drive loop formation and breakdown events. Conversely, once looped, the DNA-protein complex is insensitive to applied force. Our measurements are in excellent agreement with a simple polymer model of loop formation in DNA, and show that an antiparallel topology is the preferred LacI-DNA loop conformation for a generic loop-forming construct.
- Received 20 October 2009
DOI:https://doi.org/10.1103/PhysRevLett.104.048301
©2010 American Physical Society
Synopsis
Loop, de-loop
Published 1 February 2010
Relatively small tension in a DNA strand can have large effects on its ability to control the expression of genes.
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