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Author Notes:

To whom correspondence should be addressed. Tel: Phone: +1 (404) 727 4930; Fax: +1 (404) 727 0873; Email: lfinzi@emory.edu

We wish to thank Ian Dodd for reading our manuscript and providing many useful comments.

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Research Funding:

HFSPO (RGP0050/2002-C to L.F. and S.A.); Emory URC-2006 (to LF); Intramural Research Program of the National Institutes of Health, National Cancer Institute and the Center for Cancer Research (to S.A.). Funding for open access charge: SA's; Intramural Research Program of the National Institutes of Health, National Cancer Institute and the Center for Cancer Research.

Direct demonstration and quantification of long-range DNA looping by the λ bacteriophage repressor

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Journal Title:

Nucleic Acids Research

Volume:

Volume 37, Number 9

Publisher:

, Pages 2789-2795

Type of Work:

Article | Final Publisher PDF

Abstract:

Recently, it was proposed that DNA looping by the λ repressor (CI protein) strengthens repression of lytic genes during lysogeny and simultaneously ensures efficient switching to lysis. To investigate this hypothesis, tethered particle motion experiments were performed and dynamic CI-mediated looping of single DNA molecules containing the λ repressor binding sites separated by 2317 bp (the wild-type distance) was quantitatively analyzed. DNA containing all three intact operators or with mutated o3 operators were compared. Modeling the thermodynamic data established the free energy of CI octamer-mediated loop formation as 1.7 kcal/mol, which decreased to –0.7 kcal/mol when supplemented by a tetramer (octamer+tetramer-mediated loop). These results support the idea that loops secured by an octamer of CI bound at oL1, oL2, oR1 and oR2 operators must be augmented by a tetramer of CI bound at the oL3 and oR3 to be spontaneous and stable. Thus the o3 sites are critical for loops secured by the CI protein that attenuate cI expression.

Copyright information:

© 2009 The Author(s)

This is an Open Access work distributed under the terms of the Creative Commons Attribution 2.0 Generic License (http://creativecommons.org/licenses/by/2.0/).

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