Impact of benzo[a]pyrene-2'-deoxyguanosine lesions on methylation of DNA by SssI and HhaI DNA methyltransferases

The impact of stereoisomeric (+)- and (-)-trans-anti-B[a]P.[N.sup.2]-dG adducts ([B.sup.+] and [B.sup.-]) on DNA methylation by prokaryotic DNA methyltransferases M.SssI and M.HhaI are investigated. The trans-anti-B[a]P-[N.sup.2]-dG lesion when it flanks a target dC in the CpG dinucleotide sequence on its 5'-side has a greater adverse impact on methylation than the same lesion when it is 3' adjacent or opposite to the target dC.