Ling F, Makishima F, Morishima N, Shibata T
Laboratory of Cellular and Molecular Biology, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
EMBO J. 1995 Aug 15;14(16):4090-101. doi: 10.1002/j.1460-2075.1995.tb00081.x.
Homologous recombination (crossing over and gene conversion) is generally essential for heritage and DNA repair, and occasionally causes DNA aberrations, in nuclei of eukaryotes. However, little is known about the roles of homologous recombination in the inheritance and stability of mitochondrial DNA which is continuously damaged by reactive oxygen species, by-products of respiration. Here, we report the first example of a nuclear recessive mutation which suggests an essential role for homologous recombination in the stable inheritance of mitochondrial DNA. For the detection of this class of mutants, we devised a novel procedure, 'mitochondrial crossing in haploid', which has enabled us to examine many mutant clones. Using this procedure, we examined mutants of Saccharomyces cerevisiae that showed an elevated UV induction of respiration-deficient mutations. We obtained a mutant that was defective in both the omega-intron homing and Endo.SceI-induced homologous gene conversion. We found that the mutant cells are temperature sensitive in the maintenance of mitochondrial DNA. A tetrad analysis indicated that elevated UV induction of respiration-deficient mutations, recombination deficiency and temperature sensitivity are all caused by a single nuclear mutation (mhr1) on chromosome XII. The pleiotropic characteristics of the mutant suggest an essential role for the MHR1 gene in DNA repair, recombination and the maintenance of DNA in mitochondria.
在真核生物的细胞核中，同源重组（交叉互换和基因转换）通常对于遗传和DNA修复至关重要，偶尔也会导致DNA畸变。然而，对于同源重组在线粒体DNA的遗传和稳定性中所起的作用却知之甚少，线粒体DNA会不断受到呼吸作用副产物活性氧的损伤。在此，我们报道了首例核隐性突变的实例，该实例表明同源重组在线粒体DNA的稳定遗传中起着至关重要的作用。为了检测这类突变体，我们设计了一种新颖的方法——“单倍体中的线粒体交叉”，这使我们能够检测许多突变克隆。利用这一方法，我们检测了酿酒酵母中显示呼吸缺陷型突变的紫外线诱导率升高的突变体。我们获得了一个在ω-内含子归巢和内切酶I-SceI诱导的同源基因转换方面均有缺陷的突变体。我们发现突变细胞在维持线粒体DNA方面对温度敏感。四分体分析表明，呼吸缺陷型突变的紫外线诱导率升高、重组缺陷和温度敏感性均由位于第十二号染色体上的单个核突变（mhr1）引起。该突变体的多效性特征表明MHR1基因在DNA修复、重组以及线粒体中DNA的维持方面起着至关重要的作用。
