Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, China.
FEBS J. 2019 Nov;286(22):4542-4553. doi: 10.1111/febs.15021. Epub 2019 Aug 7.
Mitochondrial DNA encodes key subunits of the oxidative phosphorylation complexes essential for ATP production. Translation initiation in mitochondria requires two general factors, mtIF2 and mtIF3, whose counterparts in bacteria are essential for protein synthesis. In this study, we report the characterization of the fission yeast Schizosaccharomyces pombe mtIF2 (Mti2) and mtIF3 (Mti3). Deletion of mti2 impairs cell growth on the respiratory medium. The growth defect of the mti2 deletion mutant can be suppressed by expressing IFM1, the Saccharomyces cerevisiae homolog of Mti2, demonstrating functional conservation between the two proteins. Deletion of mti2 also impairs mitochondrial protein synthesis. Unlike mti2, deletion of mti3 does not affect cell growth on respiratory media and mitochondrial translation. However, deletion of mti3 exacerbates the growth defect of the Δmti2 mutant, suggesting that the two proteins have distinct, but partially overlapping functions during the process of mitochondrial translation initiation in S. pombe. Both Mti2 and Mti3 are associated with the small subunit of the mitochondrial ribosome (mitoribosome). Disruption of mti2, but not mti3, causes dissociation of the mitoribosome and also abolishes Mti3 binding to the small subunit of the mitoribosome. Our results suggest that Mti2 and Mti3 bind in a sequential manner to the small subunit of the mitoribosome and that Mti3 facilitates the function of Mti2 in mitochondrial translation initiation. Our findings also support the view that the importance of the mitochondrial translation initiation factors varies among the organisms.
线粒体 DNA 编码氧化磷酸化复合物的关键亚基，这些复合物对于 ATP 的产生至关重要。线粒体中的翻译起始需要两个通用因子，mtIF2 和 mtIF3，它们在细菌中的对应物是蛋白质合成所必需的。在这项研究中，我们报告了裂殖酵母 Schizosaccharomyces pombe mtIF2（Mti2）和 mtIF3（Mti3）的特征。mti2 的缺失会损害细胞在呼吸培养基中的生长。mti2 缺失突变体的生长缺陷可以通过表达 IFM1（Mti2 的酿酒酵母同源物）来抑制，这表明这两种蛋白之间存在功能保守性。mti2 的缺失也会损害线粒体蛋白的合成。与 mti2 不同，mti3 的缺失不会影响细胞在呼吸培养基中的生长和线粒体翻译。然而，mti3 的缺失会加剧 Δmti2 突变体的生长缺陷，表明这两种蛋白在裂殖酵母线粒体翻译起始过程中具有不同但部分重叠的功能。Mti2 和 Mti3 都与线粒体核糖体的小亚基（mitoribosome）相关。mti2 的破坏，但不是 mti3 的破坏，会导致 mitoribosome 的解离，并使 Mti3 与 mitoribosome 的小亚基结合丧失。我们的结果表明，Mti2 和 Mti3 以顺序的方式结合到 mitoribosome 的小亚基上，并且 Mti3 促进 Mti2 在线粒体翻译起始中的功能。我们的发现也支持了这样一种观点，即在不同的生物体中，线粒体翻译起始因子的重要性是不同的。
