Fast dynamics of supercoiled DNA revealed by single-molecule experiments

doi:10.1073/pnas.0700333104

Fast dynamics of supercoiled DNA revealed by single-molecule experiments

*Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands; and
^‡Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027

Edited by Xiaoliang Xie, Harvard University, Cambridge, MA, and accepted by the Editorial Board May 29, 2007 (received for review January 14, 2007)

Abstract

The dynamics of supercoiled DNA play an important role in various cellular processes such as transcription and replication that involve DNA supercoiling. We present experiments that enhance our understanding of these dynamics by measuring the intrinsic response of single DNA molecules to sudden changes in tension or torsion. The observed dynamics can be accurately described by quasistatic models, independent of the degree of supercoiling initially present in the molecules. In particular, the dynamics are not affected by the continuous removal of the plectonemes. These results set an upper bound on the hydrodynamic drag opposing plectoneme removal, and thus provide a quantitative baseline for the dynamics of bare DNA.

Footnotes

^§To whom correspondence should be addressed. E-mail: n.h.dekker{at}tudelft.nl
Author contributions: D.A.K., R.S., and N.H.D. designed research; A.C. performed research; A.C., D.A.K., and C.H.W. analyzed data; and A.C. and N.H.D. wrote the paper.
↵ ^†Present address: Biotechnological Center, University of Technology Dresden, Tatzberg 47-51, D-01307 Dresden, Germany.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. X.X. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/cgi/content/full/0700333104/DC1.
Abbreviations:

Lk,

linking number;

Wr,

writhe;

Tw,

twist.