User:CER20G/Hydroxymethylation

Hydroxymethylation in demethylation[edit]
5-Methylcytosine is a common epigenetic marker. The methyl group is modified by oxidation of the methyl group in a process called hydroxymethylation:


 * RCH3 + O → RCH2OH

This oxidation is thought to be a prelude to removal, regenerating cytosine.

Hydroxymethylation in DNA Demethylation
5-methylcytosine (5mC), a common and highly stable epigenetic marker which mediates long-term gene silencing, can be converted to 5-hydroxymethylcytosine (5hmC) via enzymatic oxidation.
 * RCH3 + O → RCH2OH

In mammals this enzymatic oxidation occurs via a family of enzymes known as TET (ten eleven translocation) methylcytosine dioxygenases; of which, there are three variants: TET1, TET2, & TET3. TET enzymes can further oxidize 5hmC to form formylcytosine (5fC) and carboxylcytosine (5caC). Recognition of 5caC and 5fC by thymine-DNA glycosylase (TDG) coupled with the base-excision repair (BER) pathway results in excision of the oxidized variant which is replaced by an unmethylated cytosine.