title: Are liquid crystalline properties of nucleosomes involved in chromosome structure and dynamics?
abstract: Nucleosome core particles correspond to the structural units of eukaryotic chromatin. They are charged colloids, 101 Angstrom in diameter and 55 Angstrom in length, formed by the coiling of a 146/147 bp DNA fragment (50 nm) around the histone protein octamer. Solutions of these particles can be concentrated, under osmotic pressure, up to the concentrations found in the nuclei of living cells. In the presence of monovalent cations (Na(+)), nucleosomes self-assemble into crystalline or liquid crystalline phases. A lamello-columnar phase is observed at 'low salt' concentrations, while a two-dimensional hexagonal phase and a three-dimensional quasi-hexagonal phase form at 'high salt' concentrations. We followed the formation of these phases from the dilute isotropic solutions to the ordered phases by combining cryoelectron microscopy and X-ray diffraction analyses. The phase diagram is presented as a function of the monovalent salt concentration and applied osmotic pressure. An alternative method to condense nucleosomes is to induce their aggregation upon addition of divalent or multivalent cations (Mg(2+), spermidine(3+) and spermine(4+)). Ordered phases are also found in the aggregates. We also discuss whether these condensed phases of nucleosomes may be relevant from a biological point of view.
authors.affiliation: Laboratoire de Physique des Solides, Bât 510, Université Paris Sud, 91405 Orsay Cedex, France. livolant@lps.u-psud.fr
authors.forename: Françoise
authors.initials: F
authors.lastname: Livolant
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Mangenot
authors.forename: Amélie
authors.initials: A
authors.lastname: Leforestier
authors.forename: Aurélie
authors.initials: A
authors.lastname: Bertin
authors.forename: Marta de
authors.initials: Md
authors.lastname: Frutos
authors.forename: Eric
authors.initials: E
authors.lastname: Raspaud
authors.forename: Dominique
authors.initials: D
authors.lastname: Durand
mesh_terms: D000818:Animals; D002412:Cations; D002417:Cattle; D002875:Chromosomes / Q000737:chemistry* / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D005614:Freeze Fracturing; D066298:In Vitro Techniques; D050866:Liquid Crystals; D046911:Macromolecular Substances; D008958:Models, Molecular; D009707:Nucleosomes / Q000737:chemistry* / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D002412:Cations; D046911:Macromolecular Substances; D009707:Nucleosomes