Mitochondrial RNA polymerase is needed for activation of the origin of light-strand DNA replication

Mol Cell. 2010 Jan 15;37(1):67-78. doi: 10.1016/j.molcel.2009.12.021.


Mitochondrial DNA is replicated by a unique enzymatic machinery, which is distinct from the replication apparatus used for copying the nuclear genome. We examine here the mechanisms of origin-specific initiation of lagging-strand DNA synthesis in human mitochondria. We demonstrate that the mitochondrial RNA polymerase (POLRMT) is the primase required for initiation of DNA synthesis from the light-strand origin of DNA replication (OriL). Using only purified POLRMT and DNA replication factors, we can faithfully reconstitute OriL-dependent initiation in vitro. Leading-strand DNA synthesis is initiated from the heavy-strand origin of DNA replication and passes OriL. The single-stranded OriL is exposed and adopts a stem-loop structure. At this stage, POLRMT initiates primer synthesis from a poly-dT stretch in the single-stranded loop region. After about 25 nt, POLRMT is replaced by DNA polymerase gamma, and DNA synthesis commences. Our findings demonstrate that POLRMT can function as an origin-specific primase in mammalian mitochondria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Replication*
  • DNA, Mitochondrial / biosynthesis*
  • DNA, Mitochondrial / chemistry
  • DNA-Directed RNA Polymerases / physiology*
  • Gene Silencing
  • Humans
  • Models, Genetic
  • Nucleic Acid Conformation
  • Poly T / chemistry
  • Replication Origin


  • DNA, Mitochondrial
  • Poly T
  • DNA-Directed RNA Polymerases
  • POLRMT protein, human