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While DNA methylation does not have the flexibility required for the fine-tuning of gene regulation, its stability is perfect to ensure the permanent silencing of transposable elements. [33] Transposon control is one of the most ancient functions of DNA methylation that is shared by animals, plants and multiple protists. [34]
DNA methylation is the conversion of the cytosine to 5-methylcytosine. The formation of Me-CpG is catalyzed by the enzyme DNA methyltransferase. In vertebrates, DNA methylation typically occurs at CpG sites (cytosine-phosphate-guanine sites—that is, sites where a cytosine is directly followed by a guanine in the DNA sequence).
During repair of DNA damages some individual repair events can alter the methylation of DNA and/or the acetylations or methylations of histones at the sites of damage, and thus can contribute to leaving an epigenetic scar on chromatin. [20] Such epigenetic scars likely contribute to the persistent epigenetic changes found in addiction.
Cis-regulatory DNA sequences that are located in DNA regions distant from the promoters of genes can have very large effects on gene expression, with some genes undergoing up to 100-fold increased expression due to such a cis-regulatory sequence. [36] These cis-regulatory sequences include enhancers, silencers, insulators and tethering elements ...
In mammals, DNA methylation occurs almost exclusively at a cytosine that is followed by a guanine. DNA methylation is a widespread mechanism for epigenetic influence on gene expression and is seen in bacteria and eukaryotes and has roles in heritable transcription silencing and transcription regulation. Methylation most often occurs on a ...
Variation in methylation states of DNA can alter gene expression levels significantly. Methylation variation usually occurs through the action of DNA methylases. When the change is heritable, it is considered epigenetic. When the change in information status is not heritable, it would be a somatic epitype. The effective information content has ...
The genomic DNA of eukaryotic cells is wrapped around special protein molecules known as Histones. The complexes formed by the looping of the DNA are known as chromatin . The basic structural unit of chromatin is the nucleosome : this consists of the core octamer of histones (H2A, H2B, H3 and H4) as well as a linker histone and about 180 base ...
Such modifications affect the binding affinity between histones and DNA, and thus loosening or tightening the condensed DNA wrapped around histones, e.g., Methylation of specific lysine residues in H3 and H4 causes further condensation of DNA around histones, and thereby prevents binding of transcription factors to the DNA that lead to gene ...