•Gene
promoter-region DNA methylation
–An important mechanism for storage of epigenetic information is DNA methylation, a process by means of which sites adjacent to genes on
chromosomes (promoter regions) are chemically
methylated after a cycle of DNA replication.
(Addition of a methyl group to the 5 position of the cytosine ring in a cytosine guanine
basepair (CpG))
–Methylation is carried out by DNA methyltransferases using S-adenosyl-methionine (SAM) as a methyl group donor.
–Methylation is inheritable - passed on in the course of cell divisions and through generations of people.
–Methylation
generally suppresses gene expression by
•physically
impeding transcription of proteins. or
•recruiting
other CpG binding proteins that change histone structure.
–Occurs in
60-90% of genes.
–Transcriptional silencing due to gene methylation is a central action required for a number of basic biological processes including embryonic
development, protection against intragenomic
parasites, X-inactivation, genomic imprinting and cognitive functions.
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