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Histone Variants at the Centromere

Histone Variants at the Centromere

Histone variants are the histone proteins with structural and sequence variations. These variants may be regarded as “mutant” forms that replace their canonical histone counterparts in the nucleosomes. Specific post-translational modifications on the histone variants enable further chromatin complexity and regulate tissue-specific gene expression. The most common histone variants are from histone H2A, H2B, and linker histone H1 families. However, several variants of histone H3 variants are also...

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.
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 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

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...

The Nucleosome

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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.
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Related Experiment Video

Updated: Jul 11, 2026

Immunofluorescence Analysis of Endogenous and Exogenous Centromere-kinetochore Proteins

Immunofluorescence Analysis of Endogenous and Exogenous Centromere-kinetochore Proteins

Published on: March 3, 2016

Structure, dynamics, and evolution of centromeric nucleosomes.

Yamini Dalal¹, Takehito Furuyama, Danielle Vermaak

¹Basic Sciences Division and Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA.

Proceedings of the National Academy of Sciences of the United States of America

|September 26, 2007

Summary

This summary is machine-generated.

Centromeric nucleosomes in Drosophila are hemisomes, not octamers. This unique structure, featuring centromere-specific histone variant (CenH3), explains key centromere functions and evolution.

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Last Updated: Jul 11, 2026

Immunofluorescence Analysis of Endogenous and Exogenous Centromere-kinetochore Proteins

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Probing The Structure And Dynamics Of Nucleosomes Using Atomic Force Microscopy Imaging

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Assembly of Nucleosomal Arrays from Recombinant Core Histones and Nucleosome Positioning DNA

Assembly of Nucleosomal Arrays from Recombinant Core Histones and Nucleosome Positioning DNA

Published on: September 10, 2013

Area of Science:

Molecular Biology
Epigenetics
Chromatin Biology

Background:

Centromeres are crucial for chromosome segregation in eukaryotes.
Centromeric nucleosomes contain a unique histone variant, centromere-specific histone (CenH3), replacing canonical H3.
The precise structure of centromeric nucleosomes has been debated.

Purpose of the Study:

To determine the structural unit of centromeric nucleosomes in interphase Drosophila cells.
To investigate how centromeric nucleosome structure influences centromere function.
To propose an evolutionary model for centromeric nucleosome differentiation.

Main Methods:

Analysis of nucleosome composition in Drosophila melanogaster.
Structural characterization of centromeric nucleosomes.
Comparative analysis with canonical nucleosomes.

Main Results:

Centromeric nucleosomes are heterotypic tetramers, termed "hemisomes," composed of CenH3, H4, H2A, and H2B.
This hemisome structure, unlike canonical octameric nucleosomes, explains kinetochore accessibility and epigenetic inheritance.
Structural differences, particularly in loop 1, favor tetramer formation with CenH3 over octamers with H3.

Conclusions:

The hemisome model provides a unifying explanation for enigmatic centromere properties.
Asymmetric hemisomes may facilitate kinetochore assembly and regulate chromatin condensation.
This differentiation mechanism likely evolved early in eukaryotic history from an archaea-like ancestor.