Nucleosome chiral transition under positive torsional stress in single chromatin fibers.

Aurélien Bancaud (1) , Gaudeline Wagner (1) , Natalia Conde E Silva (2) , Christophe Lavelle (2, 3) , Hua Wong (3) , Julien Mozziconacci (3) , Maria Barbi (3) , Andrei Sivolob (4) , Eric Le Cam (5) , Liliane Mouawad (6) , Jean-Louis Viovy (1) , Jean-Marc Victor (3) , Ariel Prunell (2)

1 PCC - Physico-Chimie-Curie
2 IJM (UMR_7592) - Institut Jacques Monod
3 LPTMC - Laboratoire de Physique Théorique de la Matière Condensée
4 Department of General and Molecular Genetics, Taras Shevchenko National University
5 IMC (UMR 8126) - Interactions moléculaires et cancer
6 Imagerie intégrative de la molécule à l'organisme

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.

Domaines: Biochimie, Biologie Moléculaire

Aurélien Bancaud, Gaudeline Wagner, Natalia Conde E Silva, Christophe Lavelle, Hua Wong, et al.. Nucleosome chiral transition under positive torsional stress in single chromatin fibers.. Molecular Cell, 2007, 27 (1), pp.135-47. ⟨10.1016/j.molcel.2007.05.037⟩. ⟨hal-00181873⟩