Tension induces a base-paired overstretched DNA conformation
Journal article, 2012

Mixed-sequence DNA molecules undergo mechanical overstretching by approximately 70% at 60-70 pN. Since its initial discovery 15 y ago, a debate has arisen as to whether the molecule adopts a new form [Cluzel P, et al. (1996) Science 271: 792-794; Smith SB, Cui Y, Bustamante C (1996) Science 271: 795-799], or simply denatures under tension [van Mameren J, et al. (2009) Proc Natl Acad Sci USA 106: 18231-18236]. Here, we resolve this controversy by using optical tweezers to extend small 60-64 bp single DNA duplex molecules whose base content can be designed at will. We show that when AT content is high (70%), a force-induced denaturation of the DNA helix ensues at 62 pN that is accompanied by an extension of the molecule of approximately 70%. By contrast, GC-rich sequences (60% GC) are found to undergo a reversible overstretching transition into a distinct form that is characterized by a 51% extension and that remains base-paired. For the first time, results proving the existence of a stretched basepaired form of DNA can be presented. The extension observed in the reversible transition coincides with that produced on DNA by binding of bacterial RecA and human Rad51, pointing to its possible relevance in homologous recombination.


mechanism of recombination

single molecule


double helix

mechanical properties of DNA


DNA stretching


terminal alkynes


elongated DNA


structural transitions




Niklas Bosaeus

Chalmers, Chemical and Biological Engineering, Physical Chemistry

Afaf El-Sagheer

University of Southampton

T. Brown

University of Southampton

S. B. Smith

University of California

Björn Åkerman

Chalmers, Chemical and Biological Engineering, Physical Chemistry

C. Bustamante

University of California

Bengt Nordén

Chalmers, Chemical and Biological Engineering, Physical Chemistry

Proceedings of the National Academy of Sciences of the United States of America

0027-8424 (ISSN) 1091-6490 (eISSN)

Vol. 109 38 15179-15184

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)


Life Science Engineering (2010-2018)

Materials Science

Subject Categories

Chemical Sciences



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