Molecular function

Catalysis of the reaction: 5-methylcytosine (5mC) in DNA + 2-oxoglutarate + O2 = 5-hydroxymethylcytosine (5hmC) in DNA + succinate + CO2. This reaction is the first step in the removal of cytosine methylated on position 5 in double-stranded DNA. This activity can iteratively oxidize 5hmC to 5-formylcytosine (5fC) and to 5-carboxylcytosine (5caC).

This reaction removes the methyl group from position 5 of cytosine in DNA via oxidation of the 5-methylcytosine, followed by removal of the oxidated base by the base excision repair system. Do not confuse with oxidative DNA demethylase activity ; GO:0035516, which directly reverses the alkylation on nucleodides in the DNA.