Replicating animal mitochondrial DNA

Abstract

The field of mitochondrial DNA (mtDNA) replication has been experiencing incredible progress in recent years, and yet little is certain about the mechanism(s) used by animal cells to replicate this plasmid-like genome. The long-standing strand-displacement model of mammalian mtDNA replication (for which single-stranded DNA intermediates are a hallmark) has been intensively challenged by a new set of data, which suggests that replication proceeds via coupled leading- and lagging-strand synthesis (resembling bacterial genome replication) and/or via long stretches of RNA intermediates laid on the mtDNA lagging-strand (the so called RITOLS). The set of proteins required for mtDNA replication is small and includes the catalytic and accessory subunits of DNA polymerase γ, the mtDNA helicase Twinkle, the mitochondrial single-stranded DNA-binding protein, and the mitochondrial RNA polymerase (which most likely functions as the mtDNA primase). Mutations in the genes coding for the first three proteins are associated with human diseases and premature aging, justifying the research interest in the genetic, biochemical and structural properties of the mtDNA replication machinery. Here we summarize these properties and discuss the current models of mtDNA replication in animal cells.

Extra-telomeric Functions of Human Telomerase: Cancer, Mitochondria and Oxidative Stress

“…Thus, it is also difficult to speculate about any potential biological activity of TERT as a reverse transcriptase within mitochondria. However, one could speculate that it could be involved in nucleic acid metabolism within mitochondria, which is still not well understood in mammals [154].…”

Minireview: DNA replication in plant mitochondria

“…After replication of the first strand is nearly two-thirds completed, the other DNA strand is copied by staggered replication (Bogenhagen and Clayton, 2003). Animal mtDNA also replicates by a bidirectional replication mechanism termed strand-coupled replication or by a third mechanism termed RITOLS (Bowmaker et al, 2003; Fish et al, 2004; reviewed by McKinney and Oliveira, 2013). All three models of human mtDNA replication utilize the same origins of replication, but vary in the amount of RNA retained in the newly synthesized DNA strand.…”

“…However, a mitochondrial DNA primase has never been conclusively identified in human mitochondria. It has been proposed that partially processed transcripts synthesized by mitochondrial RNA polymerase may serve as primers and remain in the newly made DNA, eliminating the need for a DNA primase (McKinney and Oliveira, 2013; Reyes et al, 2013). …”

“…In mammals there are three nuclear-encoded enzymes required for mtDNA replication: DNA Polγ (DNA polymerase gamma), Twinkle helicase, and single-stranded DNA binding proteins (McKinney and Oliveira 2013). Lethal mutations occur when either Polγ or Twinkle genes become nonfunctional (Wanrooij et al, 2004).…”

Biochemical Characterization of the Human Mitochondrial Replicative Twinkle Helicase

“…Twinkle helicase collaborates with DNA polymerase ␥ (pol ␥A) 2 and its associated processivity factor (pol ␥B) and the mitochondrial single-stranded DNA-binding protein as the minimally reconstituted mtDNA replisome (3). Although there has been much debate and interest in the mechanism(s) underlying mtDNA synthesis, it is generally thought, based on experimental evidence, that strand displacement DNA synthesis occurs for both the light and heavy guanine-rich strands of the circular doublestranded mitochondrial genome (4). Because there are two origins of replication for the heavy and light strands, a threestranded displacement loop structure known as the D-loop was created.…”