O6-Methyl-2’-deoxyguanosine is a ubiquitous DNA lesion formed by xenobiotic carcinogens and endogenous methylating agent, S-adenosyl-L-methionine. A mutagenic adducts formed by a potent tobacco carcinogen, 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).