Dynamics of the DNA duplex formation studied by single
molecule force measurements
Ulrich Bockelmann 1*, Philippe Thomen 2 and Francois Heslot 2
1 LPA ENS
2 LPA ENS
* To whom correspondence should be addressed. E-mail: ulrich{at}lpa.ens.fr.
Submitted on January 12, 2004
Revised on March 1, 2004
Accepted on 25 August 2004
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Abstract |
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DNA is partly denatured in-vitro by applying a force that mechanically separates the two strands of the double helix. Sudden reduction of the imposed displacement triggers spontaneous reannealing of the molecule. The corresponding force signals are measured by optical trapping interferometry for backward steps of various amplitudes and base sequence intervals. The measured signals frequently show plateaus of varying duration at discrete values that are dependent on the base sequence. Additional measurements are performed with proteins bound to the double helix. When the opening fork encounters such protein during mechanical unzipping, force increases until the protein is ejected. This ejection induces fast release of tension and fast unzipping. Comparing our different measurements, we find that both DNA unzipping and the relaxation of tension in DNA are faster than the formation of the double helix.
Key Words:
dna protein interaction, force, refolding dna, single molecule
