The Role of 3′-5′ Exonucleolytic Proofreading and Mismatch Repair in Yeast Mitochondrial DNA Error Avoidance
In the D171G/D230A mutant generated at conserved aspartate residues in the Exo1 and Exo2 sites of the 3′-5′ exonuclease domain of the yeast mitochondrial DNA (mtDNA) polymerase (pol-γ), the mitochondrial genome is unstable and the frequency of mtDNA point mutations is 1500 times higher than in the w...
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Veröffentlicht in: | The Journal of biological chemistry 1998-09, Vol.273 (37), p.23690-23697 |
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Sprache: | eng |
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Zusammenfassung: | In the D171G/D230A mutant generated at conserved aspartate residues in the Exo1 and Exo2 sites of the 3′-5′ exonuclease domain of the yeast mitochondrial DNA (mtDNA) polymerase (pol-γ), the mitochondrial genome is unstable and the frequency of mtDNA point mutations is 1500 times higher than in the wild-type strain and 10 times higher than in single substitution mutants. The 104-fold decrease in the 3′-5′ exonuclease activity of the purified mtDNA polymerase is associated with mismatch extension and high rates of base misincorporation. Processivity of the purified polymerase on primed single-stranded DNA is decreased and theKm for dNTP is increased. The sequencing of mtDNA point mutations in the wild-type strain and in proofreading and mismatch-repair deficient mutants shows that mismatch repair contributes to elimination of the transitions while exonucleolytic proofreading preferentially repairs transversions, and more specifically A to T (or T to A) transversions. However, even in the wild-type strain, A to T (or T to A) transversions are the most frequent substitutions, suggesting that they are imperfectly repaired. The combination of both mismatch repair and proofreading deficiencies elicits a mitochondrial error catastrophe. These data show that the faithful replication of yeast mtDNA requires both exonucleolytic proofreading and mismatch repair. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.273.37.23690 |