O6-Methyldeoxyguanosine triphosphate (m6dGTP), known to be produced in vivo by methylation of deoxyguanosine triphosphate with simple methylating mutagens, is utilized by prokaryotic DNA polymerases during in vitro replication of synthetic and natural DNA templateprimers. A study of the kinetic behavior of m6dGTP during DNA replication in vitro and of its effect on DNA replication indicates that m6dGTP acts as an analogue of dATP with Km app of about 6 μM for Escherichia coli DNA polymerase I (Klenow fragment) ompared to the Km app of about 0.8 μM for dATP. m6dGTP is not incorporated in the complete absence of dATP (a competitive inhibitor). m6dGTP also inhibits in vitro DNA synthesis. Different DNA polymerases behave differently in utilization and turnover of m6dGTP. T4 DNA polymerase shows stronger discrimination against m6dGMP incorporation than either T5 DNA polymerase or E. coli DNA polymerase I. The possibility that m6dGTP is unlikely to contribute significantly to in vivo mutation is discussed.
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