TI - AlkB -mediated repair of 1-meG lesions . AB - When previously studying the ability of AlkB to repair RNA , we used [3H] MNU-treated RNA oligonucleotide ( 23 ) and [14C] MeI-treated tRNA as subSTRates ( 15 ) , and AlkB repaired these two SUBstrates at similar efficiencies . Here , we have analysed the contents of methylated bases in these SUBstrates by subjecting the constituent nucleosides to HPLC analysis , and some important differences were noticed . In the case of the [3H] MNU-treated oligonucleotide SUBstrate , the major lesions introduced were 1-meA , 3-meC and 7-meG , and , as expected , AlkB -mediated removal was only observed in the case of 1-meA and 3-meC (Figure 4A) . However , when the nucleosides from the [14C] MeI-treated tRNA were analysed by HPLC , two additional peaks were observed ( Figure 4B ) . One of these peaks coeluted with a nucleoside standard corresponding to 1-meG and was removed by the AlkB treatment . We have not established the identity of the second peak , which was not affected by the AlkB treatment . Our data indicate that 1-meG is a major lesion introduced by MeI treatment of tRNA , and that this lesion is efficiently removed by AlkB treatment .