Courtesy of Richard Roberts, New England Biolabs |
![]() Model methylation reaction: Cytosine nucleotide (red) is flipped out of the DNA double helix by a methyltransferase (white), so it can be methylated. The end product after the methyl group has been transferred to the DNA is pictured in green. |
The term methylation refers to the addition of a methyl group to the cyclic carbon 5 of a cytosine nucleotide. A family of conserved DNA methyltransferases catalyzes this reaction. Basically, the methyl group tags a gene so it is turned off, and an unnecessary protein product is not produced in a particular cell. For instance, one of the two X chromosomes in female mammals is inactivated by methylation.
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