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.
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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.
Regulation occurs at the TATA box.
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).
Histones are water-soluble.
Histones have been evolutionarily conserved.
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.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.Structure
Proteins rich in lysine and arginine.Details
In general, genes that are active have less bound histone, while inactive genes are highly associated with histones during interphase.History
Discovered in 1884 by Albrecht Kossel.