title: Nucleosome chiral transition under positive torsional stress in single chromatin fibers.
abstract: Using magnetic tweezers to investigate the mechanical response of single chromatin fibers, we show that fibers submitted to large positive torsion transiently trap positive turns at a rate of one turn per nucleosome. A comparison with the response of fibers of tetrasomes (the [H3-H4](2) tetramer bound with approximately 50 bp of DNA) obtained by depletion of H2A-H2B dimers suggests that the trapping reflects a nucleosome chiral transition to a metastable form built on the previously documented right-handed tetrasome. In view of its low energy, <8 kT, we propose that this transition is physiologically relevant and serves to break the docking of the dimers on the tetramer that in the absence of other factors exerts a strong block against elongation of transcription by the main RNA polymerase.
authors.affiliation: Institut Curie, CNRS-UMR 168, 75231 Paris Cedex 05, France.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bancaud
authors.forename: Gaudeline
authors.initials: G
authors.lastname: Wagner
authors.forename: Natalia
authors.initials: N
authors.lastname: Conde E Silva
authors.forename: Christophe
authors.initials: C
authors.lastname: Lavelle
authors.forename: Hua
authors.initials: H
authors.lastname: Wong
authors.forename: Julien
authors.initials: J
authors.lastname: Mozziconacci
authors.forename: Maria
authors.initials: M
authors.lastname: Barbi
authors.forename: Andrei
authors.initials: A
authors.lastname: Sivolob
authors.forename: Eric
authors.initials: E
authors.lastname: Le Cam
authors.forename: Liliane
authors.initials: L
authors.lastname: Mouawad
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Viovy
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Victor
authors.forename: Ariel
authors.initials: A
authors.lastname: Prunell
mesh_terms: D001696:Biomechanical Phenomena; D008565:Membrane Proteins; D008954:Models, Biological; D009707:Nucleosomes / Q000378:metabolism* / Q000648:ultrastructure; D012399:Rotation; D013997:Time Factors; D014102:Torsion Abnormality
chemical_list: D008565:Membrane Proteins; D009707:Nucleosomes