TI - Repair of 3-methylthymine and 1-methylguanine lesions by bacterial and human AlkB proteins . AB - The Escherichia coli AlkB protein repairs 1-methyladenine ( 1-meA ) and 3-methylcytosine ( 3-meC ) lesions in DNA and RNA by oxidative demethylation , a reaction requiring ferrous iron and 2-oxoglutarate as cofactor and co-SUBstrate , respectively . Here , we have studied the activity of AlkB proteins on 3-methylthymine ( 3-meT ) and 1-methylguanine ( 1-meG ) , two minor lesions which are structurally analogous to 1-meA and 3-meC . AlkB as well as the human AlkB homologues , hABH2 and hABH3 , were all able to demethylate 3-meT in a DNA oligonucleotide containing a single 3-meT residue . Also , 1-meG lesions introduced by chemical methylation of tRNA were efficiently removed by AlkB . Unlike 1-meA and 3-meC , nucleosides or bases corresponding to 1-meG or 3-meT did not stimulate the uncoupled , AlkB -mediated decarboxylation of 2-oxoglutarate . Our data show that 3-meT and 1-meG are repaired by AlkB , but indicate that the recognition of these SUBstrates is different from that in the case of 1-meA and 3-meC .