In vivo occupancy of mitochondrial single-stranded DNA binding protein supports the strand displacement mode of DNA replication

PLoS Genet. 2014 Dec 4;10(12):e1004832. doi: 10.1371/journal.pgen.1004832. eCollection 2014 Dec.


Mitochondrial DNA (mtDNA) encodes for proteins required for oxidative phosphorylation, and mutations affecting the genome have been linked to a number of diseases as well as the natural ageing process in mammals. Human mtDNA is replicated by a molecular machinery that is distinct from the nuclear replisome, but there is still no consensus on the exact mode of mtDNA replication. We here demonstrate that the mitochondrial single-stranded DNA binding protein (mtSSB) directs origin specific initiation of mtDNA replication. MtSSB covers the parental heavy strand, which is displaced during mtDNA replication. MtSSB blocks primer synthesis on the displaced strand and restricts initiation of light-strand mtDNA synthesis to the specific origin of light-strand DNA synthesis (OriL). The in vivo occupancy profile of mtSSB displays a distinct pattern, with the highest levels of mtSSB close to the mitochondrial control region and with a gradual decline towards OriL. The pattern correlates with the replication products expected for the strand displacement mode of mtDNA synthesis, lending strong in vivo support for this debated model for mitochondrial DNA replication.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Helicases / genetics
  • DNA Helicases / metabolism
  • DNA Polymerase gamma
  • DNA Replication*
  • DNA, Mitochondrial / genetics
  • DNA, Mitochondrial / metabolism*
  • DNA, Single-Stranded / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • DNA-Directed DNA Polymerase / genetics
  • DNA-Directed DNA Polymerase / metabolism
  • DNA-Directed RNA Polymerases / genetics
  • DNA-Directed RNA Polymerases / metabolism
  • HeLa Cells
  • Humans
  • Mitochondria / genetics*
  • Mitochondria / metabolism
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism
  • Recombination, Genetic
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • DNA, Mitochondrial
  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Mitochondrial Proteins
  • SSBP1 protein, human
  • TFAM protein, human
  • Transcription Factors
  • DNA-Directed RNA Polymerases
  • POLRMT protein, human
  • DNA Polymerase gamma
  • DNA-Directed DNA Polymerase
  • POLG protein, human
  • POLG2 protein, human
  • DNA Helicases
  • TWNK protein, human

Grant support

The reported research was funded by Swedish Research Council ( grants 2012-2583, 2013-4409, and 2013-3621; the Swedish Cancer Foundation (; European research council ( grants GENEMIT and REPMIT; and a Knut and Alice Wallenbergs foundation ( project grant for anti-obesity therapy. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.