Nucleosome chiral transition under positive torsional stress in single chromatin fibers.
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.
Bancaud
Aurélien
A
Institut Curie, CNRS-UMR 168, 75231 Paris Cedex 05, France.
Wagner
Gaudeline
G
Conde E Silva
Natalia
N
Lavelle
Christophe
C
Wong
Hua
H
Mozziconacci
Julien
J
Barbi
Maria
M
Sivolob
Andrei
A
Le Cam
Eric
E
Mouawad
Liliane
L
Viovy
Jean-Louis
JL
Victor
Jean-Marc
JM
Prunell
Ariel
A
D001696:Biomechanical Phenomena; D008565:Membrane Proteins; D008954:Models, Biological; D009707:Nucleosomes / Q000378:metabolism* / Q000648:ultrastructure; D012399:Rotation; D013997:Time Factors; D014102:Torsion Abnormality
D008565:Membrane Proteins; D009707:Nucleosomes