5-carboxylcytosine (5caC) is the final oxidized derivative of 5-methylcytosine (5mC). 5mC is oxidized to 5-hydroxymethylcytosine (5hmC) which is then oxidized to 5-formylcytosine (5fC) then 5caC. Each of these oxidation steps are catalyzed by the Ten-Eleven Translocation (TET) family of enzymes. 5fC can then be further oxidized to 5-carboxylcytosine (5caC) by TET. Both 5fC and 5caC can be converted to unmodified cytosine by Terminal deoxynucleotidyl transferase (TdT) or Thymine DNA glycosylase (TDG) by base excision repair.
