Tension induces a base-paired overstretched DNA conformation

Niklas Bosaeus, Afaf H. El-Sagheer, Tom Brown, Steven B. Smith, Bjorn Akerman, Carlos Bustamante, Bengt Norden

Research output: Contribution to journalArticlepeer-review

69 Scopus citations

Abstract

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.
Original languageEnglish (US)
Pages (from-to)15179-15184
Number of pages6
JournalPROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume109
Issue number38
DOIs
StatePublished - 2012
Externally publishedYes

ASJC Scopus subject areas

  • General

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