%0 Journal Article
%T Nucleosome Chiral Transition under Positive Torsional Stress in Single Chromatin Fibers
%A Aurelien Bancaud
%A Gaudeline Wagner
%A Natalia Conde e Silva
%A Christophe Lavelle
%A Hua Wong
%A Julien Mozziconacci
%A Maria Barbi
%A Andrei Sivolob
%A Eric Le Cam
%A Liliane Mouawad
%A Jean-Louis Viovy
%A Jean-Marc Victor
%A Ariel Prunell
%J Quantitative Biology
%D 2007
%I arXiv
%R 10.1016/j.molcel.2007.05.037
%X 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 ~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 righthanded tetrasome. In view of its low energy, <8 kT, we propose this transition is physiologically relevant and serves to break the docking of the dimers on the tetramer which in the absence of other factors exerts a strong block against elongation of transcription by the main RNA polymerase.
%U http://arxiv.org/abs/0708.0156v2