Biased incorporation of ribonucleotides on the mitochondrial L-strand accounts for apparent strand-asymmetric DNA replication

Cell. 2002 Nov 15;111(4):495-505. doi: 10.1016/s0092-8674(02)01075-9.


Recently, we presented evidence for conventional, strand-coupled replication of mammalian mitochondrial DNA. Partially single-stranded replication intermediates detected in the same DNA preparations were assumed to derive from the previously described, strand-asymmetric mode of mitochondrial DNA replication. Here, we show that bona fide replication intermediates from highly purified mitochondria are essentially duplex throughout their length, but contain widespread regions of RNA:DNA hybrid, as a result of the incorporation of ribonucleotides on the light strand which are subsequently converted to DNA. Ribonucleotide-rich regions can be degraded to generate partially single-stranded molecules by RNase H treatment in vitro or during DNA extraction from crude mitochondria. Mammalian mitochondrial DNA replication thus proceeds mainly, or exclusively, by a strand-coupled mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • DNA Replication / physiology*
  • DNA, Mitochondrial / physiology*
  • DNA, Single-Stranded
  • DNA-Binding Proteins / metabolism
  • Mitochondria, Liver*
  • Nucleic Acid Hybridization
  • RNA
  • RNA, Mitochondrial
  • Rats
  • Ribonuclease H / metabolism
  • Ribonucleotides / physiology
  • Single-Strand Specific DNA and RNA Endonucleases / metabolism


  • DNA, Mitochondrial
  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • RNA, Mitochondrial
  • Ribonucleotides
  • RNA
  • Ribonuclease H
  • Single-Strand Specific DNA and RNA Endonucleases