Removal of 8-oxo-GTP by MutT hydrolase is not a major contributor to transcriptional fidelity

Living in an oxygen-rich environment is dangerous for a cell. Reactive oxygen species can damage DNA, RNA, protein and lipids. The MutT protein in Escherichia coli removes 8-oxo-deoxyguanosine triphosphate (8-oxo-dGTP) and 8-oxo-guanosine triphosphate (8-oxo-GTP) from the nucleotide pools precluding incorporation into DNA and RNA. While 8-oxo-dGTP incorporation into DNA is mutagenic, it is not clear if 8-oxo-GTP incorporation into RNA can have phenotypic consequences for the cell. We use a bistable epigenetic switch sensitive to transcription errors in the Escherichia coli lacI transcript to monitor transient RNA errors. We do not observe any increase in epigenetic switching in mutT cells. We revisit the original observation of partial phenotypic suppression of a lacZ(amber) allele in amutT background that was attributed to RNA errors. We find that Lac(+) revertants can completely account for the increase in beta-galactosidase levels in mutT lacZ(amber) cultures, without invoking participation of transient transcription errors. Moreover, we observe a fluctuation type of distribution of beta-galactosidase appearance in a growing culture, consistent with Lac(+) DNA revertant events. We conclude that the absence of MutT produces a DNA mutator but does not equally create an RNA mutator.