Unravelling the structural plasticity of stretched DNA under torsional constraint.
Regions of the genome are often held under torsional constraint. Nevertheless, the influence of such constraint on DNA-protein interactions during genome metabolism is still poorly understood. Here using a combined optical tweezers and fluorescence microscope, we quantify and explain how torsional constraint influences the structural stability of DNA under applied tension. We provide direct evidence that concomitant basepair melting and helical unwinding can occur in torsionally constrained DNA at forces >∼50 pN. This striking result indicates that local changes in linking number can be absorbed by the rest of the DNA duplex. We also present compelling new evidence that an overwound DNA structure (likely P-DNA) is created (alongside underwound structures) at forces >∼110 pN. These findings substantiate previous theoretical predictions and highlight a remarkable structural plasticity of torsionally constrained DNA. Such plasticity may be required in vivo to absorb local changes in linking number in DNA held under torsional constraint.
Department of Physics and Astronomy and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Graeme A
GA
King
Department of Physics and Astronomy and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Erwin J G
EJ
Peterman
Department of Physics and Astronomy and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Gijs J L
GJ
Wuite
D020029:Base Pairing / Q000235:genetics; D001483:Base Sequence; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D052898:Optical Tweezers; D009994:Osmolar Concentration; D013816:Thermodynamics; D054159:Torsion, Mechanical
D004247:DNA