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Nucleosome Remodeling

Nucleosome Remodeling

Nucleosomes are the basic units of chromatin compaction. Each nucleosome consists of the DNA bound tightly around a histone core, which makes the DNA inaccessible to DNA binding proteins such as DNA polymerase and RNA polymerase. Hence, the fundamental problem is to ensure access to DNA when appropriate, despite the compact and protective chromatin structure.
Nucleosome remodeling complex
Eukaryotic cells have specialized enzymes called ATP-dependent nucleosome remodeling enzymes. These enzymes...

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...

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...

Spreading of Chromatin Modifications

Spreading of Chromatin Modifications

The histone proteins in the nucleosomes are post-translationally modified (PTM) to increase or decrease access to DNA. The commonly observed PTMs are methylation, acetylation, phosphorylation, and ubiquitination of lysine amino acids in the histone H3 tail region. These histone modifications have specific meaning for the cell. Hence, they are called "histone code". The protein complex involved in histone modification is termed as "reader-writer" complex.
Writers
The writer...

Separation of Sister Chromatids

Separation of Sister Chromatids

At the transition from prophase to metaphase, there is a reduction in cohesion along the chromosomal arms, resulting in the resolution of sister chromatids. However, residual cohesin connections remain to hold the sister chromatids together until the transition from metaphase to anaphase. The residual connection prevents any premature separation of sister chromatids, blocking the risks of aneuploidy within the daughter cells.
At the onset of anaphase, separase, a proteolytic enzyme, is...

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...

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Related Experiment Video

Updated: Jul 12, 2025

Reconstitution of Nucleosomes with Differentially Isotope-labeled Sister Histones

Reconstitution of Nucleosomes with Differentially Isotope-labeled Sister Histones

Published on: March 26, 2017

Phosphorylated HP1α-Nucleosome Interactions in Phase Separated Environments.

Nesreen Elathram¹, Bryce E Ackermann¹, Evan T Clark¹

¹Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States.

Journal of the American Chemical Society

|October 23, 2023

Summary

Phosphorylated HP1α protein interacts with methylated histone tails, regulating heterochromatin without altering nucleosome structure. This provides atomic insights into phase separation in gene silencing.

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Area of Science:

Molecular Biology
Epigenetics
Biophysics

Background:

Transcriptionally silent genes are organized into heterochromatin.
Heterochromatin involves nucleosomes with specific histone modifications (H3K9me3) and proteins like HP1α.
HP1α can form liquid-like droplets, suggesting phase separation drives heterochromatin organization, influenced by phosphorylation.

Purpose of the Study:

To investigate the molecular interactions of phosphorylated HP1α with nucleosomes during phase separation.
To understand how HP1α influences nucleosome structure and dynamics in heterochromatin.

Main Methods:

Solution and solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
Analysis of phosphorylated human HP1α interactions with nucleosomes.

Main Results:

Phosphorylated human HP1α does not significantly rearrange the nucleosome core.
HP1α specifically binds to methylated H3 tails.
HP1α slows down the dynamics of H4 tails.

Conclusions:

Phosphorylated HP1α regulates the heterochromatin landscape through specific interactions with histone tails.
The study provides an atomic-level understanding of a complex, dynamic biological system involving phase separation and post-translational modifications.