The cellular DNA precursor pool was shown to be a target for N-methyl-N-nitrosourea, a potent mutagen and carcinogen. O6medGTP, a product of this interaction, was chemically synthesized and shown to be incorporated into DNA in vitro by Klenow E. coli pol I and phage T4 DNA polymerases. O6medGTP incorporated predominantly opposite T template residues and to a lower extent opposite C. At some loci incorporation of O6medGTP caused DNA synthesis arrest. The significance of the behavior of O6medGTP for mutagenesis in vivo is discussed.
