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Histone
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Histone

In biology, histones are the chief proteins of chromatin. They act as spools around which DNA winds and they play a role in gene regulation.

Table of contents
1 Location
2 Classes
3 Functions
4 Structure
5 Details
6 History
7 Etymology
8 See also

Location

Histones are found in the nuclei of eukaryotic cells. Bacteria do not have histones. However, the DNA of the genus Thermoplasma (in the domain Archaea) is surrounded by a highly basic DNA-binding protein which strongly resembles the eukaryotic histones.

Classes

Five histone classes are known: Two each of class H2A, H2B, H3 and H4 assemble to form one nucleosome, together with DNA. H1 is needed for histone-DNA-complexes to form a 30-nm fiber, which packs the DNA even more tightly.

Functions

They act as spools around which DNA winds and they play a role in gene regulation.

DNA compaction

Histones act as spools for DNA. This enables the compaction necessary to fit the large genomes of eukaryotes inside cell nuclei.

Gene regulation

Histones act in gene regulation. Histones can undergo posttranslational modifications. These modifications can play a role in gene regulation in an epigenetic manner.

Regulation occurs at the TATA box.

Structure

Proteins rich in lysine and arginine.

Histones are subject to posttranslational modification by enzymes primarily on their N-terminal tails, but also in their globular domains. Such modifications include methylation, acetylation, phosphorylation, ubiquitination, and ADP-ribosylation. This effects their function of gene regulation (see Functions).

Details

In general, genes that are active have less bound histone, while inactive genes are highly associated with histones during interphase.

Histones are water-soluble.

Histones have been evolutionarily conserved.

History

Discovered in 1884 by Albrecht Kossel.

Until the early 1990's, histones were dismissed as merely packing material for nuclear DNA. During the early 1990's, the regulatory functions of histones were discovered.

Etymology

Late 19th century. From German Histon , of uncertain origin: perhaps from Greek histanai or from histos

See also