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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.

Histones are found in the nuclei of eukaryotic cells. Bacteria do not have histones, but histones are found in certain Archaea, namely Euryarchaea. These archaeal histones are evolutionary precursors to the eukaryotic histones.

1 Classes

Six histone classes are known:

H1 (sometimes called H5.)
H2A
H2B
H3
H4

Archaeal histones

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.

2 Functions

Histones act as spools around which DNA winds and they play a role in gene regulation. This enables the compaction necessary to fit the large genomes of eukaryotes inside cell nuclei. 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 boxA TATA box is a DNA sequence cis element) found in the promoter region of most genes (it is considered to be a promoter sequence). It is the binding site of either transcription factors or histones (binding of one blocks binding of the other). It has the.

3 Structure

The proteins comprising histones are rich in lysine and arginine and are water-soluble. Histones are subject to posttranslational modification by enzymes primarily on their N-terminal tails, but also in their globular domains. Such modifications include methylationMethylation is the addition of a methyl group to any substrate. When used in the context of epigenetics, methylation can refer to the addition of a methyl group to a cytosine residue of DNA to convert it to 5-methylcytosine or the addition of a methyl gro, acetylationAcetylation describes a reaction, usually with acetic acid, that introduces an acetyl radical into an organic compound. Moreover, it is that process of introducing an acetyl group into a compound, specifically, the substitution of an acetyl radical for an, phosphorylationIn biochemistry, phosphorylation is the addition of a phosphate (PO) group to a protein or a small molecule. Its prominent role in biochemistry is the subject of a very large body of research (the Medline database returns over 100,000 articles on the subj, ubiquitination, and ADP-ribosylation. This effects their function of gene regulation (see functions).

In general, genes that are active have less bound histone, while inactive genes are highly associated with histones during interphase. It also appears that the structure of histones have been evolutionarily conserved.

4 History

Histones were discovered in 1884 by Albrecht Kossel. The word "histone" dates from the late 19th century and is from the German "Histon", of uncertain origin: perhaps from Greek histanai or from histos. Until the early 1990s, histones were dismissed as merely packing material for nuclear DNA. During the early 1990s, the regulatory functions of histones were discovered.

5 See also

Genetics Proteins

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Topics: Histone, Classes, Functions, Structure, History, See Also...

HistoneIn biology, histones are the chief proteins of chromatin. They act as spools around which DNA winds and they play a role in gene regulation. Histones are found in the nuclei of eukaryotic cells. Bacteria do not have histones, but histones are found in cer	Histone methyltransferaseHistone methyltransferases (HMT) are enzymes which catalyze the transfer of one to three methyl groups from the cofactor s-adenosylmethionine to lysine and arginine residues of histone proteins. These proteins have been characterized by a SET (Su(var)3-9,	Histone geneA histone gene is a gene that codes for histone.
Histone acetyltransferaseHistone acetyltransferase is an enzyme that mediates histone acetylation.	Histone octamerA histone octamer is an octamer of histones found at the center of a nucleosome core particle. It consists of 2 H2A, 2 H2B, 2 H3, and 2 H4. These histones of the histone octamer all contain N-terminal tails that emanate from their central histone folds, a	Histone foldA histone fold is a fold found near the C-terminus of each type histone in a histone octamer.

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