Colby G, Wu M, Tzagoloff A
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
J Biol Chem. 1998 Oct 23;273(43):27945-52. doi: 10.1074/jbc.273.43.27945.
Mutations in MTO1 express a respiratory defect only in the context of a mitochondrial genome with a paromomycin-resistance allele. This phenotype is similar to that described previously for mss1 mutants by Decoster, E., Vassal, A., and Faye, G. (1993) J. Mol. Biol. 232, 79-88. We present evidence that Mto1p and Mss1p are mitochondrial proteins and that they form a heterodimer complex. In a paromomycin-resistant background, mss1 and mto1 mutants are inefficient in processing the mitochondrial COX1 transcript for subunit 1 of cytochrome oxidase. The mutants also fail to synthesize subunit 1 and show a pleiotropic absence of cytochromes a, a3, and b. In vivo pulse labeling of an mto1 mutant, however, indicate increased rates of synthesis of other mitochondrial translation products. The respiratory defective phenotype of mto1 and mss1 mutants is not seen in a paromomycin-sensitive genetic background. The visible absorption spectra of such strains indicate a higher ratio of cytochromes b/a and elevated NADH- and succinate-cytochrome c reductase activities. To explain these phenotypic characteristics, we proposed that the Mto1p.Mss1p complex plays a role in optimizing mitochondrial protein synthesis in yeast, possibly by a proofreading mechanism.
只有在具有巴龙霉素抗性等位基因的线粒体基因组背景下，MTO1中的突变才会表现出呼吸缺陷。这种表型与Decoster、E.、Vassal、A.和Faye、G.（1993年）《分子生物学杂志》232卷，79 - 88页先前描述的mss1突变体的表型相似。我们提供证据表明Mto1p和Mss1p是线粒体蛋白，并且它们形成异二聚体复合物。在抗巴龙霉素的背景下，mss1和mto1突变体在处理细胞色素氧化酶亚基1的线粒体COX1转录本方面效率低下。这些突变体也无法合成亚基1，并且表现出细胞色素a、a3和b的多效性缺失。然而，对mto1突变体的体内脉冲标记表明其他线粒体翻译产物的合成速率增加。在对巴龙霉素敏感的遗传背景中未观察到mto1和mss1突变体的呼吸缺陷表型。此类菌株的可见吸收光谱表明细胞色素b/a的比例更高，并且NADH - 细胞色素c还原酶和琥珀酸 - 细胞色素c还原酶活性升高。为了解释这些表型特征，我们提出Mto1p.Mss1p复合物在优化酵母中的线粒体蛋白质合成中发挥作用，可能是通过校对机制。
