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Expression of a proof-reading deficient form of mitochondrial DNA (mtDNA) polymerase gamma, POLG, causes early death accompanied by features of premature ageing in mouse. However, the mechanism of cellular senescence remains unresolved. In addition to high levels of point mutations of mtDNA, the POLG mutator mouse harbours linear mtDNAs. Using one- and two-dimensional agarose gel electrophoresis, we show that the linear mtDNAs derive from replication intermediates and are indicative of replication pausing and chromosomal breakage at the accompanying fragile sites. Replication fork arrest is not random but occurs at specific sites close to two cis-elements known as O(H) and O(L). Pausing at these sites may be enhanced in the case of exonuclease-deficient POLG owing to delayed resumption of DNA replication, or replisome instability. In either case, the mtDNA replication cycle is perturbed and this might explain the progeroid features of the POLG mutator mouse.

Original publication

DOI

10.1093/nar/gkp091

Type

Journal article

Journal

Nucleic Acids Res

Publication Date

04/2009

Volume

37

Pages

2327 - 2335

Keywords

Animals, Chromosome Breakage, Chromosome Fragile Sites, DNA Replication, DNA, Mitochondrial, DNA-Directed DNA Polymerase, Female, Liver, Mice, Mice, Mutant Strains, Mitochondria, Progeria, Sequence Analysis, DNA, Single-Strand Specific DNA and RNA Endonucleases