The incorporation of O6-methyldeoxyguanosine monophosphate and O4-methyldeoxythymidine monophosphate into polynucleotide templates leads to errors during subsequent in vitro DNA synthesis.

O4-MedTMP and O6-MedGMP may be incorporated from their 5'-triphosphates into polynucleotides by DNA polymerases. Once incorporated O6-MedGMP leads to errors during further cycles of DNA synthesis with a mutagenic efficiency of 0.3-0.7, the value depending upon the relative dNTP concentrations in the assay. In contrast O4-MedTMP leads to very few errors following its incorporation into DNA. The results demonstrate that O6-MedGMP, once incorporated into DNA, should be destined to give rise to DNA base changes during the second round of DNA synthesis.