Editing CpG site (section)

=== Methylation of CpG islands stably silences genes ===

In humans, DNA methylation occurs at the 5 position of the pyrimidine ring of the cytosine residues within CpG sites to form [[5-methylcytosine]]s. The presence of multiple methylated CpG sites in CpG islands of promoters causes stable silencing of genes.<ref name=Bird>{{cite journal |vauthors=[[Adrian Bird|Bird A]] |title=DNA methylation patterns and epigenetic memory |journal=Genes Dev. |volume=16 |issue=1 |pages=6–21 |year=2002 |pmid=11782440 |doi=10.1101/gad.947102 |doi-access=free }}</ref> Silencing of a gene may be initiated by other mechanisms, but this is often followed by methylation of CpG sites in the promoter CpG island to cause the stable silencing of the gene.<ref name=Bird />