Chromatin conformation and salt-induced compaction: three-dimensional structural information from cryoelectron microscopy

Détails

ID Serval
serval:BIB_03468B7C0346
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Institution
Titre
Chromatin conformation and salt-induced compaction: three-dimensional structural information from cryoelectron microscopy
Périodique
Journal of Cell Biology
Auteur(s)
Bednar  J., Horowitz  R. A., Dubochet  J., Woodcock  C. L.
ISSN
0021-9525 (Print)
Statut éditorial
Publié
Date de publication
12/1995
Volume
131
Numéro
6 Pt 1
Pages
1365-76
Notes
Journal Article
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S. --- Old month value: Dec
Résumé
Cryoelectron microscopy has been used to examine the three-dimensional (3-D) conformation of small oligonucleosomes from chicken erythrocyte nuclei after vitrification in solutions of differing ionic strength. From tilt pairs of micrographs, the 3-D location and orientation of the nucleosomal disks, and the paths of segments of exposed linker can be obtained. In "low-salt" conditions (5 mM NaCl, 1 mM EDTA, pH 7.5), the average trinucleosome assumes the shape of an equilateral triangle, with nucleosomes at the vertices, and a length of exposed linker DNA between consecutive nucleosomes equivalent to approximately 46 bp. The two linker DNA segments converge at the central nucleosome. Removal of histones H1 and H5 results in a much more variable trinucleosome morphology, and the two linker DNA segments usually join the central nucleosome at different locations. Trinucleosomes vitrified in 20 mM NaCl, 1 mM EDTA, (the salt concentration producing the maximal increase in sedimentation), reveal that compaction occurs by a reduction in the included angle made by the linker DNA segments at the central nucleosome, and does not involve a reduction in the distance between consecutive nucleosomes. Frequently, there is also a change in morphology at the linker entry-exit site. At 40 mM NaCl, there is no further change in trinucleosome morphology, but polynucleosomes are appreciably more compact. Nevertheless, the 3-D zig-zag conformation observed in polynucleosomes at low salt is retained at 40 mM NaCl, and individual nucleosome disks remain separated from each other. There is no evidence for the formation of solenoidal arrangements within polynucleosomes. Comparison of the solution conformation of individual oligonucleosomes with data from physical measurements on bulk chromatin samples suggests that the latter should be reinterpreted. The new data support the concept of an irregular zig-zag chromatin conformation in solution over a range of ionic strengths, in agreement with other in situ (McDowall, A.W., J.M. Smith, and J. Dubochet. 1986, EMBO (Eur. Mol. Biol. Organ.) J.5: 1395-1402; Horowitz, R.A., D.A. Agard, J.W. Sedat, and C.L. Woodcock, 1994. J. Cell Biol. 125:1-10), and in vitro conclusions (van Holde, K., and J. Zlatanova. 1995. J. Biol. Chem. 270:8373-8376). Cryoelectron microscopy also provides a way to determine the 3-D conformation of naturally occurring chromatins in which precise nucleosome positioning plays a role in transcriptional regulation.
Mots-clé
Animals Chickens Chromatin/chemistry/*ultrastructure DNA/chemistry Freezing Histones/chemistry Microscopy, Electron/methods Nucleic Acid Conformation Nucleosomes/chemistry *Protein Conformation Sodium Chloride/*chemistry/pharmacology
Pubmed
Web of science
Open Access
Oui
Création de la notice
24/01/2008 10:25
Dernière modification de la notice
20/08/2019 12:25
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