1. Structure of an H1-Bound 6-Nucleosome Array Reveals an Untwisted Two-Start Chromatin Fiber Conformation.
- Author
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Garcia-Saez I, Menoni H, Boopathi R, Shukla MS, Soueidan L, Noirclerc-Savoye M, Le Roy A, Skoufias DA, Bednar J, Hamiche A, Angelov D, Petosa C, and Dimitrov S
- Subjects
- Animals, Binding Sites, Cloning, Molecular, Cryoelectron Microscopy, Crystallography, X-Ray, DNA genetics, DNA metabolism, Escherichia coli genetics, Escherichia coli metabolism, Gene Expression, Genetic Vectors chemistry, Genetic Vectors metabolism, Histones genetics, Histones metabolism, Humans, Hydroxyl Radical chemistry, Models, Molecular, Nucleosome Assembly Protein 1 genetics, Nucleosome Assembly Protein 1 metabolism, Nucleosomes chemistry, Nucleosomes metabolism, Osmolar Concentration, Protein Binding, Protein Conformation, alpha-Helical, Protein Conformation, beta-Strand, Protein Interaction Domains and Motifs, Protein Multimerization, Recombinant Proteins chemistry, Recombinant Proteins genetics, Recombinant Proteins metabolism, Xenopus laevis, DNA chemistry, Histones chemistry, Nucleosome Assembly Protein 1 chemistry, Nucleosomes ultrastructure
- Abstract
Chromatin adopts a diversity of regular and irregular fiber structures in vitro and in vivo. However, how an array of nucleosomes folds into and switches between different fiber conformations is poorly understood. We report the 9.7 Å resolution crystal structure of a 6-nucleosome array bound to linker histone H1 determined under ionic conditions that favor incomplete chromatin condensation. The structure reveals a flat two-start helix with uniform nucleosomal stacking interfaces and a nucleosome packing density that is only half that of a twisted 30-nm fiber. Hydroxyl radical footprinting indicates that H1 binds the array in an on-dyad configuration resembling that observed for mononucleosomes. Biophysical, cryo-EM, and crosslinking data validate the crystal structure and reveal that a minor change in ionic environment shifts the conformational landscape to a more compact, twisted form. These findings provide insights into the structural plasticity of chromatin and suggest a possible assembly pathway for a 30-nm fiber., (Copyright © 2018 Elsevier Inc. All rights reserved.)
- Published
- 2018
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