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Science 3 January 1992:
Vol. 255. no. 5040, pp. 82 - 85
DOI: 10.1126/science.1553534
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Articles

Science, Vol 255, Issue 5040, 82-85
Copyright © 1992 by American Association for the Advancement of Science

articles

Torsional rigidity of positively and negatively supercoiled DNA

PR Selvin, DN Cook, NG Pon, WR Bauer, MP Klein, and JE Hearst

Department of Physics, University of California, Berkeley.

Time-correlated single-photon counting of intercalated ethidium bromide was used to measure the torsion constants of positively supercoiled, relaxed, and negatively supercoiled pBR322 DNA, which range in superhelix density from +0.042 to -0.123. DNA behaves as coupled, nonlinear torsional pendulums under superhelical stress, and the anharmonic term in the Hamiltonian is approximately 15 percent for root-mean-square fluctuations in twist at room temperature. At the level of secondary structure, positively supercoiled DNA is significantly more flexible than negatively supercoiled DNA. These results exclude certain models that account for differential binding affinity of proteins to positively and negatively supercoiled DNA.


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J. Neurosci. 19, 5898-5909
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Femtosecond dynamics of the DNA intercalator ethidium and electron transfer with mononucleotides in water.
T. Fiebig, C. Wan, S. O. Kelley, J. K. Barton, and A. H. Zewail (1999)
PNAS 96, 1187-1192
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Supercoiling affects the accessibility of glutathione to DNA-bound molecules: Positive supercoiling inhibits calicheamicin-induced DNA damage.
W. A. LaMarr, L. Yu, K. C. Nicolaou, and P. C. Dedon (1998)
PNAS 95, 102-107
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A Role of Basic Residues and the Putative Intercalating Phenylalanine of the HMG-1 Box B in DNA Supercoiling and Binding to Four-way DNA Junctions.
M. Stros and E. Muselikova (2000)
J. Biol. Chem. 275, 35699-35707
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