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Chromatin reconstitution on small DNA rings. I
I Goulet1, Y Zivanovic, A Prunell
1Centre National de la Recherche Scientifique, Université Paris VII, Institut Jacques Monod, France.
Journal of Molecular Biology
|March 20, 1988
Summary
Histone-DNA interactions in chromatin reconstitution are influenced by DNA topology. Nucleosome formation efficiency and structure depend on linking differences and salt concentrations, impacting chromatin organization.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- Chromatin, the complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells, plays a crucial role in genome organization and regulation.
- Understanding the fundamental principles of nucleosome formation and chromatin assembly is essential for deciphering gene expression and DNA-related processes.
Purpose of the Study:
- To investigate the influence of DNA topology, specifically linking difference, on the efficiency and products of chromatin reconstitution using core histones.
- To characterize the structural and conformational properties of reconstituted mono- and dinucleosomes, including their morphologies and salt-dependent behaviors.
Main Methods:
- Chromatin reconstitution using the four core histones on circular DNA templates (nicked and closed rings) with varying linking differences.
- Characterization of reconstituted nucleosomes using gel electrophoresis, sucrose gradient sedimentation, and high-resolution electron microscopy.
- Analysis of salt-dependent structural transitions in mono- and dinucleosomes.
Main Results:
- Reconstitution efficiency peaked at a linking difference of -2 turns, with distinct preferences for monomer versus dimer formation at different topoisomers.
- Two dinucleosome subtypes were identified, suggesting sequential formation and potential issues with histone octamer assembly in the second nucleosome.
- Mono- and dinucleosomes exhibited salt-dependent structural changes, adopting distinct morphologies (DNA crossing or non-crossing) influencing their arrangement on DNA rings.
Conclusions:
- DNA topology significantly impacts chromatin reconstitution efficiency and the formation of nucleosome monomers and dimers.
- The small size of the DNA ring may affect histone octamer co-operativity during dinucleosome formation.
- Nucleosome structure is conformationally dynamic and sensitive to ionic strength, influencing the spatial arrangement of nucleosomes on DNA.