5-Formylcytosines (5-fC) DNA Matched Antibody Pair Reference: REV-31-1369-MK 5-Formylcytosine (5fC) is a pyrimidine nitrogen base derived from cytosine and a recently discovered modification of DNA. Just as 5-hydroxymethylcytosine (5-hmC) is generated when the Tet family of cytosine oxygenase enzymes converts 5-methylcytosine (5-mC), it has been shown that continued activity of the Tet proteins on hydroxymethylcytosine will generate 5-formylcytosine (5-fC) and 5-carboxylcytosine. It is believed that this conversion process may represent a pathway of DNA demethylation.