In vitro miscoding of alkylthymines with DNA and RNA polymerases.

A series of poly(dT,RdT) polynucleotides containing O2-, 3- and O4-methyl- or ethyldeoxythymines have been prepared and used as templates for Pol I, Pol alpha and Pol R to investigate the miscoding properties of these modified bases with the different nucleotide polymerising enzymes. Only O4-alkylthymine (O4-RT) leads to a large number of errors (incorporation of dGMP with a mutagenic efficiency approaching unity). O2-RT has a very much lower, but none-the-less significant, mutagenic efficiency and 3-RT does not lead to errors with the DNA polymerases. All alkylthymines lead to significant errors with the RNA polymerase. The results confirm conclusions concerning the promutagenic nature of the alkylthymines and that the reported differences in their promutagenicity with the various polymerases reflect different specificities of the nucleotide polymerising enzymes used.