Elimination of rNMPs from mitochondrial DNA has no effect on its stability

Proc Natl Acad Sci U S A. 2020 Jun 23;117(25):14306-14313. doi: 10.1073/pnas.1916851117. Epub 2020 Jun 8.


Ribonucleotides (rNMPs) incorporated in the nuclear genome are a well-established threat to genome stability and can result in DNA strand breaks when not removed in a timely manner. However, the presence of a certain level of rNMPs is tolerated in mitochondrial DNA (mtDNA) although aberrant mtDNA rNMP content has been identified in disease models. We investigated the effect of incorporated rNMPs on mtDNA stability over the mouse life span and found that the mtDNA rNMP content increased during early life. The rNMP content of mtDNA varied greatly across different tissues and was defined by the rNTP/dNTP ratio of the tissue. Accordingly, mtDNA rNMPs were nearly absent in SAMHD1-/- mice that have increased dNTP pools. The near absence of rNMPs did not, however, appreciably affect mtDNA copy number or the levels of mtDNA molecules with deletions or strand breaks in aged animals near the end of their life span. The physiological rNMP load therefore does not contribute to the progressive loss of mtDNA quality that occurs as mice age.

Keywords: SAMHD1; dNTP pool; mitochondrial DNA; mtDNA; ribonucleotide incorporation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • DNA Damage
  • DNA, Mitochondrial / genetics*
  • DNA, Mitochondrial / metabolism*
  • Female
  • Gene Dosage
  • Genomic Instability / physiology*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Nucleotides
  • Ribonucleotides / genetics*
  • Ribonucleotides / metabolism*
  • SAM Domain and HD Domain-Containing Protein 1 / genetics


  • DNA, Mitochondrial
  • Nucleotides
  • Ribonucleotides
  • SAM Domain and HD Domain-Containing Protein 1
  • Samhd1 protein, mouse