TY - JOUR
T1 - Tension induces a base-paired overstretched DNA conformation
AU - Bosaeus, Niklas
AU - El-Sagheer, Afaf H.
AU - Brown, Tom
AU - Smith, Steven B.
AU - Akerman, Bjorn
AU - Bustamante, Carlos
AU - Norden, Bengt
N1 - KAUST Repository Item: Exported on 2021-09-17
Acknowledgements: This work was funded by grants to B.N. from the European Research Council and King Abdullah University of Science and Technology.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.
PY - 2012
Y1 - 2012
N2 - 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.
AB - 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.
UR - http://hdl.handle.net/10754/671281
UR - http://www.pnas.org/lookup/doi/10.1073/pnas.1213172109
UR - http://www.scopus.com/inward/record.url?scp=84866544846&partnerID=8YFLogxK
U2 - 10.1073/pnas.1213172109
DO - 10.1073/pnas.1213172109
M3 - Article
SN - 0027-8424
VL - 109
SP - 15179
EP - 15184
JO - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
JF - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
IS - 38
ER -