title: Secondary structure of double-stranded DNA under stretching: elucidation of the stretched form.
abstract: Almost two decades ago, measurements of force versus extension on isolated double-stranded DNA molecules revealed a force plateau. This unusual stretching phenomenon in DNA suggests that the long molecules may be extended from the usual B form into a new conformation. Different models have been proposed to describe the nature of DNA in its stretched form, S-DNA. Using atomic force microscopy combined with a molecular combing method, we identified the structure of λ-phage DNA for different stretching values. We provide strong evidence for the existence of a first-order transition between B form and S form. Beyond a certain extension of the natural length, DNA molecules adopt a new double-helix conformation characterized by a diameter of 1.2 nm and a helical pitch of 18 nm.
authors.affiliation: Institut Charles Sadron, CNRS, University of Strasbourg, 23 rue du Loess, BP 84087, F-67034 Strasbourg Cedex 2, France. mounir.maaloum@ics-cnrs.unistra.fr
authors.forename: M
authors.initials: M
authors.lastname: Maaloum
authors.forename: A-F
authors.initials: AF
authors.lastname: Beker
authors.forename: P
authors.initials: P
authors.lastname: Muller
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics; D001703:Biophysics / Q000379:methods*; D004247:DNA / Q000737:chemistry*; D007091:Image Processing, Computer-Assisted; D008024:Ligands; D018625:Microscopy, Atomic Force / Q000379:methods; D008968:Molecular Conformation; D009690:Nucleic Acid Conformation; D012984:Software
chemical_list: D008024:Ligands; D004247:DNA