Catalysis of the reaction: methylcytosine + 2-oxoglutarate + O2 = 5-hydroxymethylcytosine + succinate + CO2
1. PMID 193723912. Reactome: R-HSA-5220952 "TET1,2,3 oxidizes 5-formylcytosine to 5-carboxylcytosine"
3. Reactome: R-HSA-5220990 "TET1,2,3 oxidizes 5-hydroxymethylcytosine to 5-formylcytosine"
4. Reactome: R-HSA-5221014 "TET1,2,3 oxidizes 5-methylcytosine to 5-hydroxymethylcytosine"