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Updated: Jun 20, 2026
14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Electron microscopic and biochemical evidence that chromatin structure is a repeating unit
Cell
|April 1, 1975
Summary
Chromatin
Area of Science:
- Molecular Biology
- Biochemistry
- Cell Biology
Background:
- Chromatin is the complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.
- Histones are the main protein components of chromatin, involved in packaging DNA into structural units called nucleosomes.
- Lysine-rich histones play a crucial role in the structural organization of chromatin.
Purpose of the Study:
- To elucidate the fundamental structure of chromatin, particularly its nucleosome organization.
- To investigate the role of different histones in chromatin structure and DNA compaction.
- To explore the self-assembling properties of chromatin.
Main Methods:
- Electron microscopy was used to visualize chromatin structure at high resolution.
- Biochemical studies, including centrifugation, were employed to separate and analyze chromatin fractions.
- In vitro reconstitution experiments were performed to test chromatin self-assembly.
Main Results:
- Chromatin, depleted of lysine-rich histones, forms a flexible chain of spherical nucleosomes (125 A diameter) connected by DNA.
- Two fractions were identified: one with condensed DNA in nucleosomes, and another with free DNA connecting packed nucleosomes.
- Isolated nucleosomes contain ~200 base pairs of DNA and histones F2alpha1, F2alpha2, F2b, and F3, compacting DNA over fivefold.
- Histone F1 appears involved in the superpacking of DNA in chromosomes and nuclei.
- Chromatin fiber exhibits self-assembly properties, reconstitutable in vitro from DNA and core histones.
Conclusions:
- The fundamental unit of chromatin is the nucleosome, forming a flexible chain structure.
- Histone F1 plays a role in higher-order chromatin compaction beyond nucleosome formation.
- Chromatin structure demonstrates self-assembly capabilities, highlighting the intrinsic properties of DNA and core histones.
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