A cluster of pathogenic mutations in the 3'-5' exonuclease domain of DNA polymerase gamma defines a novel module coupling DNA synthesis and degradation
(2011)
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- Authors
- Supervisors
- Foury, Françoise
- Abstract
- (en) DNA polymerase gamma (pol g in human, Mip1 in yeast) is the unique DNA replicase found in mitochondria. Pol g plays a key role in fidelity of mtDNA replication through accurate selection of nucleotides and 3’-5’ exonuclease proofreading activity. Defective maintenance of mtDNA leads to mitochondrial dysfunction and disease. More than 150 POLG mutations have been identified in human. Based on the good conservation of the pol g catalytic subunits we have used Mip1 as a model enzyme to generate yeast mutations equivalent to seven human pol g mutations associated with PEO, various neuropathies and Alpers syndrome. Five mutations clustered in a novel subdomain of the 3’-5’ exonuclease are localized in the DNA-binding channel. We have determined the in vivo phenotypes of the yeast mutants and biochemical properties of mutant polymerases. The mip1 mutations increase the frequency of mtDNA point mutations and deletions with generally a good correlation between mtDNA instability in yeast and disease severity in human. Mutations clustered in the novel module result in increased frequency of point mutations and high instability of the mitochondrial DNA in yeast cells, and unexpectedly for mutator mutations, they favour exonucleolysis versus polymerization. This trait is associated with highly decreased DNA binding activity and poorly processive DNA synthesis. Our data show for the first time that a 3’-5’ exonuclease module of DNA polymerase gamma plays a crucial role in the coordination of the polymerase and exonuclease functions and they strongly suggest that in patients the disease is not caused by defective proofreading but results from poor mtDNA replication generated by a severe imbalance between DNA synthesis and degradation.
- Affiliations
Citations
Szczepanowska, K. (2011). A cluster of pathogenic mutations in the 3′-5′ exonuclease domain of DNA polymerase gamma defines a novel module coupling DNA synthesis and degradation. https://hdl.handle.net/2078.5/151428