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DNA methylation of transposable elements has been known to be related to genome expansion. However, the evolutionary driver for genome expansion remains unknown. There is a clear correlation between the size of the genome and CpG, suggesting that the DNA methylation of transposable elements led to a noticeable increase in the mass of DNA. [36]
Methylation of histones can either increase or decrease transcription of genes, depending on which amino acids in the histones are methylated, and how many methyl groups are attached. Methylation events that weaken chemical attractions between histone tails and DNA increase transcription because they enable the DNA to uncoil from nucleosomes so ...
Methylation of histones may either increase or decrease gene transcription depending on which histone is modified, the amino acid that is modified, and the number of methyl groups added. [11] In the case of lysine methylation, three types of modifications exist: monomethylated, dimethylated, or trimethylated lysines.
CpG islands constitute regulatory sequences, since if CpG islands are methylated in the promoter of a gene this can reduce or silence gene transcription. [19] DNA methylation regulates gene transcription through interaction with methyl binding domain (MBD) proteins, such as MeCP2, MBD1 and MBD2.
Stress and trauma can affect expression of transcription factors, which in turn alter DNA methylation patterns. For example, transcription factor nerve growth-induced protein A (NGFI-A, also called NAB1) is up-regulated in response to high maternal care in rodents, and down-regulated in response to low maternal care (a form of early life stress).
These DNA methyltransferases can also methylate CpG sites within the coding regions of genes, where such methylation can increase gene transcription. [34] Work with DNMT3a1 showed it preferentially localized to CpG islands bivalently marked by H3K4me3 (a transcription promoting mark) and H3K27me3 (a transcription repressive mark), coinciding ...
The cis position induces compact histones and decreases the ability of proteins to bind to the DNA, thus preventing methylation of K36 and decreasing gene transcription. Conversely, the trans position of P38 promotes a more open histone conformation, allowing for K36 methylation and leading to an increase gene transcription. [36]
(Methylation of cytosine in DNA primarily occurs where cytosine is followed by guanine in the 5' to 3' DNA sequence, a CpG site.) Methylation of CpG sites in a promoter region of a gene usually represses gene transcription, [47] while methylation of CpGs in the body of a gene increases expression. [48]