Quantitation, base identity and distribution of stably incorporated ribonucleotides in nuclear and mitochondrial DNA from murine tissues

Ribonucleotides are estimated to be the most common non-canonical nucleotides transiently incorporated in DNA. Their presence or failure of their removal can affect genome stability and mutations in factors involved in dNTP pool maintenance or ribonucleotide removal can cause Aicardi-Goutieres syndrome or promote certain human cancers. Here, we have mapped and quantitated ribonucleotides genome-wide, in nine tissues of wild-type mice. We observed tissue-specific variation in number and base identity of incorporated ribonucleotides and present evidence that a number of genomic features, such as tRNA genes, transcription start sites and G-quadruplexes, can increase the frequency of stably incorporated ribonucleotides in their proximity. Moreover, we present the non-random distribution of incorporated ribonucleotides in mtDNA and identified ribonucleotide hotspots. The study presents a framework to understand the physiological role of ribonucleotides in mammalian DNA.