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A mutation in a mitochondrial ABC transporter results in mitochondrial dysfunction through oxidative damage of
H Senbongi1, F Ling, T Shibata
1Cellular and Molecular Biology Laboratory, Riken Institute, Saitama, Japan.
Abstract:
We have isolated a Saccharomyces cerevisiae mutant that shows an increased tendency to form cytoplasmic petites (respiration-deficient rho- or rho0 mutants) in response to treatment of cells growing on a solid medium with the DNA-damaging agent methyl methane-sulfonate or ultraviolet light. The mutation in this strain, atm1-1, was found to cause a single amino acid substitution in ATM1, a nuclear gene that encodes the mitochondrial ATP-binding cassette (ABC) transporter. When the mutant cells were grown in liquid glucose medium, they accumulated free iron within the mitochondria and at the same time gave rise to spontaneous cytoplasmic petite mutants, as seen previously in cells carrying a mutation in a gene homologous to the human gene responsible for Friedreich's ataxia. Analysis of the effects of free iron and malonic acid (an inhibitor of oxidative respiration in mitochondria) on the incidence of petites among the mutant cells indicated that spontaneous induction of petites was a consequence of oxidative stress rather than a direct effect of either a defect in the ATM1 gene or the accumulation of free iron. We observed an increase in the incidence of strand breaks in the mitochondrial DNA of the atm1-1 mutant cells. Furthermore, we found that rates of induction of petites and accumulation of strand breaks in mitochondrial DNA were enhanced in the atm1-1 mutant by the introduction of another mutation, mhr1-1, which results in a deficiency in mitochondrial DNA repair. These observations indicate that spontaneous induction of petites in the atm1-1 mutant is a consequence of oxidative damage to mitochondrial DNA mediated by enhanced accumulation of mitochondrial iron.
Insights
A Saccharomyces cerevisiae mutant (atm1-1) accumulates mitochondrial iron, leading to oxidative stress and increased formation of respiration-deficient petite mutants. This mitochondrial iron accumulation causes DNA strand breaks and petite induction, exacerbated by impaired DNA repair.
Area of Science:
- Cell Biology
- Genetics
- Mitochondrial Biology
Background:
- Cytoplasmic petite mutants in Saccharomyces cerevisiae are respiration-deficient.
- Mitochondrial dysfunction can lead to petite formation.
- The ATM1 gene encodes a mitochondrial ATP-binding cassette (ABC) transporter.
Purpose of the Study:
- To investigate the mechanism behind increased petite mutant formation in a Saccharomyces cerevisiae atm1-1 mutant.
- To determine the role of mitochondrial iron accumulation and oxidative stress in petite induction.
Main Methods:
- Isolation and characterization of the atm1-1 mutant.
- Analysis of mitochondrial iron levels and petite mutant frequency.
- Assessment of mitochondrial DNA strand breaks.
- Investigating the effect of mhr1-1 mutation on petite induction and DNA damage.
Main Results:
- The atm1-1 mutant accumulates free iron within mitochondria and exhibits increased spontaneous petite mutant formation.
- Spontaneous petite induction is linked to oxidative stress, not solely to ATM1 gene defect or iron accumulation.
- Increased mitochondrial DNA strand breaks were observed in atm1-1 mutant cells.
- Impaired mitochondrial DNA repair (mhr1-1 mutation) enhanced petite induction and DNA strand breaks in the atm1-1 mutant.
Conclusions:
- Spontaneous petite induction in the atm1-1 mutant is caused by oxidative damage to mitochondrial DNA.
- This damage is mediated by enhanced accumulation of mitochondrial iron.
- The ATM1 gene plays a crucial role in maintaining mitochondrial iron homeostasis and preventing oxidative DNA damage.