Nucleic Acids Research, 2000, Vol. 28, No. 24 4956-4963
© 2000 Oxford University Press
A role for MHR1, a gene required for mitochondrial genetic recombination, in the repair of damage spontaneously introduced in yeast mtDNA
1Cellular and Molecular Biology Laboratory, RIKEN (The Institute of Physical and Chemical Research), Hirosawa 2-1, Wako-shi, Saitama 351-01, Japan, 2Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12 Nishi-6, Kita-ku, Sapporo 060, Japan and 3Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), Japan
A nuclear recessive mutant in Saccharomyces cerevisiae, mhr1-1, is defective in mitochondrial genetic recombination at 30°C and shows extensive vegetative petite induction by UV irradiation at 30°C or when cultivated at a higher temperature (37°C). It has been postulated that mitochondrial DNA (mtDNA) is oxidatively damaged by by-products of oxidative respiration. Since genetic recombination plays a critical role in DNA repair in various organisms, we tested the possibility that MHR1 plays a role in the repair of oxidatively damaged mtDNA using an enzyme assay. mtDNA isolated from cells grown under standard (aerobic) conditions contained a much higher level of DNA lesions compared with mtDNA isolated from anaerobically grown cells. Soon after a temperature shift from 30 to 37°C the number of mtDNA lesions increased 2-fold in mhr1-1 mutant cells but not in MHR1 cells. Malonic acid, which decreased the oxidative stress in mitochondria, partially suppressed both petite induction and the temperature-induced increase in the amount of mtDNA damage in mhr1-1 cells at 37°C. Thus, functional mitochondria require active MHR1, which keeps the extent of spontaneous oxidative damage in mtDNA within a tolerable level. These observations are consistent with MHR1 having a possible role in mtDNA repair.
* To whom correspondence should be addressed at: Cellular and Molecular Biology Laboratory, RIKEN (The Institute of Physical and Chemical Research), Hirosawa 2-1, Wato-shi, Saitama 351-01, Japan. Tel: +81 48 467 9537; Fax: +81 48 462 4671; Email: tshibata{at}postman.riken.go.jp
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