Histone modification
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Histone modification
histone
Histones : eukaryotes somatic protein, including the alkaline chromatin arginine and much more special basic amino acid named lysine,adding up to 1/4 amino acid residues. Because of different component and different molecular weight,histones can be mainly divided into 5 kinds: H1, H2A, H2B, H3, H4. histone eight polymer including one H1,one H2A,one H2B,and two H3s and two H4s,is the core of nucleosome,and have a half weight of nucleosome.Histone H1 combinates nucleosomes by DNA sequences, making nucleosomes bindind one by one tightly.
5 kind of histones (H1, H2A, H2B, H3, H4), in addition to N-terminal of H1 containing hydrophobic amino acids, the c-terminal containing basic amino acids, other 4 histones contain basic amino acids in the N-terminal(such as arginine, lysine),and the c-terminal contains hydrophobic amino acid (such as valine, isoleucine).
The structure of folded base sequence in the c-terminal domain has an interaction with histone molecules and is connected with intertwining of DNA. While N-terminal domain can affect DNA along with other regulatory proteins , and contains lysines, is a highly fine variable area. The N-terminal tail of Histone,expecially 15-38 amino acid residues, is the main post-translation sites, regulating the DNA of biological function.
Histone modification
the histone modification after translation will first begin in its tail, then continue in its globous domain.this kind of modification includes methylation, acylation, phosphorylation,panlation and so on. These affect the function of histone in gene regulatory .
①Methylation.
The site which histone is changed by methylation contains lysine and arginine. Lysine can bear three times of methylation,and arginine can bear two . In histone H3, there are five lysine sites can be modified by methylation.
The methylation of histone modification is mainly executed by proteins containing SET structure domain, histone methylation participate in formation of heteochromatin, gene imprinting, inactivation of X-chromosome and transcription regulation and some other kinds of main physiological function. Abnormalities of histone methylation relates to tumor and other human diseases, can activate or suppress transcriptional activity of specific gene. Research found that the function object of histone methyl transferase is not only restricting certain histone, but the non-histone can be methylated by methyl transferase, this will provide a larger space for many mechanism such as gene transcription, signal transduction, individual development and differentiation.
②Acetylation.
There are two kinds of acetylation, one kind is the acetylation of amino end in histone H1, H2A, H4, and this kind forms alpha-acetyl serine, happening after the synthesis of histone in cytoplasm in the process of entering nucleotide. Second, in certain specific position of H2A, H2B, H3, H4 amino terminal area,N6 - acetyl lysine of formation happens.
H3 · H4 acetylation can open an open chromatin structure, and enhance the gene expression. Things such as CBPöP 300、PCA F is essentially histone acetyl groups shift enzyme (HA T) in body.On the contrary, HDAC is one of component of suppression transcription complex.
③Phosphorylation.
All the components of the histone proteins can be modified by phosphorylation. In cell division, first to third serine of H1 can be modified by phosphorylation. In the mitosis period,third to sixth serine or threonine of H1 can be modified by phosphorylation .The phosphorylation of other four core histone can occur in the serine residues of amino terminal domain. The phosphorylation of histone may change the union between histone and DNA. In the process of mitosis, cell death, DNA damage repair, DNA duplicate and restructuring, phosphorylation plays a direct and important role. For example, phosphorylation of N-terminal of histone H3 may promote chromatin condense in mitosis.
Phosphorylation relying on cell cycle protein kinase in Histone H1 is the main modifying function after translation. Phosphorylation of Histone H1 can affect DNA secondary structure change and chromosome agglutinate state change. On the other hand, histone H1 of phosphorylation need DNA duplicate copy of DNA, and activate protein kinase but also promote the histone H1 of phosphorylation. Therefore, phosphorylation of histone H1 and DNA duplication exist a collaborative happen mechanism.
④ADP DNA base glycosylated.
Histone H1, H2A, H2B and H3 and polyphosphate ADP - covalent binding of DNA, RNA and base of ADP - are considered in eukaryotic cells start copying process of the trigger.
Reference :
http://baike.baidu.com/view/32445.html?tp=1_11
《组蛋白修饰调节机制的研究进展》 作者:蒋智文,刘新光,周中军