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The Nucleosome Core Particle

The Nucleosome Core Particle

Nucleosomes are the DNA-histone complex, where the DNA strand is wound around the histone core. The histone core is an octamer containing two copies of H2A, H2B, H3, and H4 histone proteins.
Nucleosomes, paradoxically, perform two opposite functions simultaneously. On the one hand, their primary aim is to protect the delicate DNA strands from physical damage and help achieve a higher compaction ratio. On the other hand, they must allow polymerase enzymes to access histone-bound DNA during...

The Nucleosome Core Particle

The Nucleosome Core Particle

Nucleosomes are the DNA-histone complex, where the DNA strand is wound around the histone core. The histone core is an octamer containing two copies of H2A, H2B, H3, and H4 histone proteins.
The paradox
Nucleosomes, paradoxically, perform two opposite functions simultaneously. On the one hand, their main responsibility is to protect the delicate DNA strands from physical damage and help achieve a higher compaction ratio. While on the other hand, they must allow polymerase enzymes to access DNA...

The Nucleosome

The Nucleosome

Human DNA is almost two meters long. However, it is compressed inside a tiny nucleus measuring only a few microns in diameter. To make this degree of compaction possible, DNA is organized into several sequential levels so that it can fit into such a tiny space. The most compact form of DNA is a chromosome that can be seen under a microscope in a dividing cell.
In a chromosome, DNA is wound twice around a protein complex called a histone octamer core, which consists of 8 histone proteins. This...

The Nucleosome

The Nucleosome

DNA in a human cell is almost 2m long and it is packed inside a tiny nucleus that is only a few microns in diameter. The level of compaction of DNA inside the nucleus is astonishing. It is organized into several sequentially higher levels of compaction to fit into such a tiny space. The most compact form of DNA is a chromosome that can be seen under a microscope in a dividing cell.
DNA is wound twice around a protein complex called histone core, that consist of 8 histone proteins. This complex...

Heterochromatin

Heterochromatin

The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions that take up more dye are called heterochromatin. Heterochromatin is further classified into two forms – constitutive heterochromatin and facultative heterochromatin.
Constitutive heterochromatin: It is a highly compact region of chromatin that is mostly concentrated in the centromere and telomere. Unlike euchromatin, the amino acid at...

Histone Modification

Histone Modification

The histone proteins have a flexible N-terminal tail extending out from the nucleosome. These histone tails are often subjected to post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitination. Particular combinations of these modifications form “histone codes” that influence the chromatin folding and tissue-specific gene expression.
Acetylation
The enzyme histone acetyltransferase adds acetyl group to the histones. Another enzyme, histone...

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Related Experiment Video

Updated: Jan 14, 2026

Evaluation of the Spatial Distribution of γH2AX following Ionizing Radiation

Evaluation of the Spatial Distribution of γH2AX following Ionizing Radiation

Published on: August 7, 2010

Structural insights into γH2Ax containing nucleosomes.

Rashmi Panigrahi^1,2,3, Ross Edwards¹, Md Touhidul Islam¹

¹Department of Biochemistry, University of Alberta, Edmonton, AB, T6G 2H7, Canada.

Nucleic Acids Research

|October 22, 2025

Summary

This summary is machine-generated.

Phosphorylation of histone H2AX signals DNA repair. Structural studies show this modification disrupts nucleosome stacking, potentially aiding chromatin decondensation for repair factor access.

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Last Updated: Jan 14, 2026

Evaluation of the Spatial Distribution of γH2AX following Ionizing Radiation

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Published on: August 7, 2010

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Quantification of γH2AX Foci in Response to Ionising Radiation

Quantification of γH2AX Foci in Response to Ionising Radiation

Published on: April 6, 2010

Area of Science:

Structural Biology
Molecular Biology
Epigenetics

Background:

Histone variant H2AX phosphorylation (γH2AX) is a key signal for DNA double-strand break repair.
BRCA1 carboxy-terminal (BRCT) domains recognize γH2AX to recruit repair proteins.

Purpose of the Study:

To elucidate the structural basis of γH2AX nucleosomes and their interactions.
To investigate how BRCT domain binding affects nucleosome structure and chromatin organization.

Main Methods:

Cryogenic electron microscopy (cryo-EM) to resolve nucleosome structures.
Geometric analysis of nucleosome stacking parameters.
Molecular simulations of BRCT-γH2AX interactions.

Main Results:

Identified three distinct parallel stacked mononucleosome structures with H4 N-terminal tail, H2B, and DNA mediating interactions.
Demonstrated that BRCT domain binding to γH2AX nucleosomes disrupts stacking.
Observed dynamic, not stable, BRCT-nucleosome interactions via cryo-EM and simulations.

Conclusions:

γH2AX nucleosome stacking is regulated by specific inter-nucleosomal contacts.
Disruption of stacking by BRCT binding may facilitate chromatin decondensation.
This decondensation could expose the nucleosomal acidic patch, promoting DNA repair factor recruitment.