Histone post-translational modifications (PTMs) are key mechanisms of epigenetics that modulate chromatin structures, termed as “histone code”. The PTMs on histone including acetylation, methylation, phosphorylation and novel acylations directly affect the accessibility of chromatin to transcription factors and other epigenetic regulators, altering genome stability, gene transcription, etc. Histone methylation occurs primarily at lysine and arginine residues on the amino terminal of core histones. Methylation of histones can either increase or decrease transcription of genes, depending on which amino acids (Lys or Arg) in the histones are methylated and how many methyl groups are attached (mono-, di-, Trimethylation on Lys, mono-di-symmetric/asymmetric methylation on Arg). Mostly, lysine methylation occurs primarily on histone H3 Lys4, 9, 27, 36, 79 and H4 Lys20, while Arginine methylation occurs primarily on histone H3 Arg2, 8, 17, 26 and H4 Arg3. histone methyltransferases (HMTs) and histone demethylases (HDMs) are major regulating factors.
Histones are basic nuclear proteins that are responsible for the nucleosome structure of the chromosomal fiber in eukaryotes. This structure consists of approximately 146 bp of DNA wrapped around a nucleosome, an octamer composed of pairs of each of the four core histones (H2A, H2B, H3, and H4). The chromatin fiber is further compacted through the interaction of a linker histone, H1, with the DNA between the nucleosomes to form higher order chromatin structures. This gene is intronless and encodes a replication-dependent histone that is a member of the histone H3 family. Transcripts from this gene lack polyA tails; instead, they contain a palindromic termination element. This gene is found in the large histone gene cluster on chromosome 6p22-p21.3.
Histone post-translational modifications (PTMs) are key mechanisms of epigenetics that modulate chromatin structures, termed as “histone code”. The PTMs on histone including acetylation, methylation, phosphorylation and novel acylations directly affect the accessibility of chromatin to transcription factors and other epigenetic regulators, altering genome stability, gene transcription, etc. Histone methylation occurs primarily at lysine and arginine residues on the amino terminal of core histones. Methylation of histones can either increase or decrease transcription of genes, depending on which amino acids (Lys or Arg) in the histones are methylated and how many methyl groups are attached (mono-, di-, trimethylation on Lys, mono-di-symmetric/asymmetric methylation on Arg). Mostly, lysine methylation occurs primarily on histone H3 Lys4, 9, 27, 36, 79 and H4 Lys20, while Arginine methylation occurs primarily on histone H3 Arg2, 8, 17, 26 and H4 Arg3. histone methyltransferases (HMTs) and histone demethylases (HDMs) are major regulating factors.
The ε-amino lysine acetylation of proteins is an important reversible modification controlling protein activity. The amino-terminal tails of core histones undergo lysine methylation in multiple sites, termed as “histone code” or “epigenetic code”. Lysine methylation in core histones is a major determinant for the formation of active and inactive regions of the genome and therefore plays vital roles in multiple cellular events. In most species, lysine methylation occurs primarily on histones H3 (Lys4, 9, 27, 36, 79) and H4 (Lys20) and has been implicated in both transcriptional activation and silencing. Methylation in histones modulated by specific histone methyltransferases (HMTs)and histone demethylases (HDMs)is impaired in the pathologies of cancer and other diseases and therefore, enzymes regulating histone lysine methylation have become promising targets for anti-cancer drugs.
Histones are a family of basic proteins that form the core of the nucleosome – the fundamental structural unit of chromatin. In a single nucleosome, core histone proteins H2A, H2B, H3, and H4 form an octamer around which the DNA is tightly wrapped. Histone proteins not only serve to compact chromosomal DNA but also play vital roles in the dynamic and long-term regulation of genes by a wide variety of post-translational modifications (PTMs). These PTMs including acetylation, methylation, phosphorylation, and novel acylations directly affect the accessibility of chromatin to transcription factors and other epigenetic regulators, altering genome stability and gene transcription. Among the histone members, histone H3 is the most extensively modified and its amino-terminal tail structure has been shown to be especially critical for eukaryotic cells.
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