Elisabeth Jemt

Publications (3)30.27 Total impact

• Article: Subnormal levels of POLγA cause inefficient initiation of light-strand DNA synthesis and lead to mitochondrial DNA deletions and autosomal dominant progressive external ophthalmoplegia.

  Sara Roos, Bertil Macao, Javier Miralles Fusté, Christopher Lindberg, Elisabeth Jemt, Elisabeth Holme, Ali-Reza Moslemi, Anders Oldfors, Maria Falkenberg
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  ABSTRACT: The POLG1 gene encodes the catalytic subunit of mitochondrial DNA (mtDNA) polymerase γ (POLγ). We here describe a sibling pair with adult-onset progressive external ophthalmoplegia, cognitive impairment and mitochondrial myopathy characterized by DNA depletion and multiple mtDNA deletions. The phenotype is due to compound heterozygous POLG1 mutations, T914P and the intron mutation c.3104 + 3A > T. The mutant genes produce POLγ isoforms with heterozygous phenotypes that fail to synthesize longer DNA products in vitro. However, exon skipping in the c.3104 + 3A > T mutant is not complete, and the presence of low levels of wild-type POLγ explains patient survival. To better understand the underlying pathogenic mechanisms, we characterized the effects of POLγ depletion in vitro and found that leading-strand DNA synthesis is relatively undisturbed. In contrast, initiation of lagging-strand DNA synthesis is ineffective at lower POLγ concentrations that uncouples leading strand from lagging-strand DNA synthesis. In vivo, this effect leads to prolonged exposure of the heavy strand in its single-stranded conformation that in turn can cause the mtDNA deletions observed in our patients. Our findings, thus, suggest a molecular mechanism explaining how POLγ mutations can cause mtDNA deletions in vivo.
  Human Molecular Genetics 03/2013; · 7.64 Impact Factor
• Source

  Available from: PubMed Central

  Article: The mitochondrial DNA helicase TWINKLE can assemble on a closed circular template and support initiation of DNA synthesis.

  Elisabeth Jemt, Géraldine Farge, Stefan Bäckström, Teresa Holmlund, Claes M Gustafsson, Maria Falkenberg
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  ABSTRACT: Mitochondrial DNA replication is performed by a simple machinery, containing the TWINKLE DNA helicase, a single-stranded DNA-binding protein, and the mitochondrial DNA polymerase γ. In addition, mitochondrial RNA polymerase is required for primer formation at the origins of DNA replication. TWINKLE adopts a hexameric ring-shaped structure that must load on the closed circular mtDNA genome. In other systems, a specialized helicase loader often facilitates helicase loading. We here demonstrate that TWINKLE can function without a specialized loader. We also show that the mitochondrial replication machinery can assemble on a closed circular DNA template and efficiently elongate a DNA primer in a manner that closely resembles initiation of mtDNA synthesis in vivo.
  Nucleic Acids Research 08/2011; 39(21):9238-49. · 8.03 Impact Factor
• Article: Mitochondrial RNA polymerase is needed for activation of the origin of light-strand DNA replication.

  Javier Miralles Fusté, Sjoerd Wanrooij, Elisabeth Jemt, Caroline E Granycome, Tricia J Cluett, Yonghong Shi, Neli Atanassova, Ian J Holt, Claes M Gustafsson, Maria Falkenberg
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  ABSTRACT: 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.
  Molecular cell 01/2010; 37(1):67-78. · 14.61 Impact Factor