Mitochondrial translation depends on mRNA-specific activators. In , DEAD-box protein Mrh5, pentatricopeptide repeat (PPR) protein Ppr4, Mtf2, and Sls1 form a stable complex (designated Mrh5C) required for translation of mitochondrial DNA (mtDNA)-encoded mRNA, the largest subunit of the cytochrome oxidase complex. However, how Mrh5C is formed and what role Mrh5C plays in mRNA translation have not been reported. To address these questions, we investigated the role of individual Mrh5C subunits in the assembly and function of Mrh5C. Our results revealed that Mtf2 and Sls1 form a subcomplex that serves as a scaffold to bring Mrh5 and Ppr4 together. Mrh5C binds to the small subunit of the mitoribosome (mtSSU), but each subunit could not bind to the mtSSU independently. Importantly, Mrh5C is required for the association of mRNA with the mtSSU. Finally, we investigated the importance of the signature DEAD-box in Mrh5. We found that the DEAD-box of Mrh5 is required for the association of Mrh5C and mRNA with the mtSSU. Unexpectedly, this motif is also required for the interaction of Mrh5 with other Mrh5C subunits. Altogether, our results suggest that Mrh5 and Ppr4 cooperate in activating the translation of mRNA. Our results also suggest that Mrh5C activates the translation of mRNA by promoting the recruitment of mRNA to the mtSSU.

中文翻译：

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Sls1 和 Mtf2 介导 cox1 mRNA 翻译激活所需的 Mrh5C 复合物的组装

线粒体翻译依赖于 mRNA 特异性激活剂。在图中，DEAD-box 蛋白 Mrh5、五肽重复 (PPR) 蛋白 Ppr4、Mtf2 和 Sls1 形成了翻译线粒体 DNA (mtDNA) 编码的 mRNA（细胞色素氧化酶复合物的最大亚基）所需的稳定复合物（称为 Mrh5C）。然而，Mrh5C是如何形成以及Mrh5C在mRNA翻译中发挥什么作用尚未见报道。为了解决这些问题，我们研究了各个 Mrh5C 亚基在 Mrh5C 组装和功能中的作用。我们的结果显示，Mtf2 和 Sls1 形成一个子复合体，充当将 Mrh5 和 Ppr4 结合在一起的支架。 Mrh5C 与线粒体核糖体小亚基 (mtSSU) 结合，但每个亚基不能独立与 mtSSU 结合。重要的是，Mrh5C 是 mRNA 与 mtSSU 关联所必需的。最后，我们研究了 Mrh5 中签名 DEAD-box 的重要性。我们发现 Mrh5 的 DEAD-box 是 Mrh5C 和 mRNA 与 mtSSU 关联所必需的。出乎意料的是，该基序也是 Mrh5 与其他 Mrh5C 亚基相互作用所必需的。总而言之，我们的结果表明 Mrh5 和 Ppr4 协同激活 mRNA 的翻译。我们的结果还表明，Mrh5C 通过促进 mRNA 募集至 mtSSU 来激活 mRNA 翻译。