dUTP incorporation into genomic DNA is linked to transcription in yeast

Highly-activated transcription is associated with eukaryotic genome instability, resulting in elevated rates of mitotic recombination and mutagenesis. The association between high transcription and genome stability is likely due to a variety of factors including an enhanced accumulation of DNA damage, transcription-associated supercoiling, collision between replication forks and the transcription machinery, and the persistence of RNA-DNA hybrids 1. In the case of transcription-associated mutagenesis (TAM), we previously showed that there is a direct proportionality between the level of transcription and the mutation rate in the yeast Saccharomyces cerevisiae2, and that the molecular nature of mutations is affected by highly-activated transcription 2 3. In the work presented here, we find that the accumulation of apurinic/apyrimidinic (AP) sites is greatly enhanced in highly-transcribed yeast DNA. We further demonstrate that most AP sites in highly-transcribed DNA are derived from the removal of uracil, the presence of which is linked to direct incorporation of dUTP in place of dTTP. These results reveal an unexpected relationship between transcription and the fidelity of DNA synthesis, and raise intriguing cell biological issues with regard to nucleotide pool compartmentalization.