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Nucleosome Chiral Transition under Positive Torsional Stress in Single Chromatin Fibers

Authors
Journal
Molecular Cell
1097-2765
Publisher
Elsevier
Publication Date
Volume
27
Issue
1
Identifiers
DOI: 10.1016/j.molcel.2007.05.037
Keywords
  • Dna
Disciplines
  • Biology

Abstract

Summary 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 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.

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