The mitoribosome, as known from studies in model organisms, deviates considerably from its ancestor, the bacterial ribosome. Deviations include substantial reduction of the mitochondrial ribosomal RNA (mt-rRNA) structure and acquisition of numerous mitochondrion-specific (M) mitoribosomal proteins (mtRPs). A broadly accepted view assumes that M-mtRPs compensate for structural destabilization of mt-rRNA resulting from its evolutionary remodeling. Since most experimental information on mitoribosome makeup comes from eukaryotes having derived mitochondrial genomes and mt-rRNAs, we tested this assumption by investigating the mitochondrial translation machinery of jakobids, a lineage of unicellular protists with the most bacteria-like mitochondrial genomes. We report here proteomics analyses of the Andalucia godoyi small mitoribosomal subunit and in silico transcriptomic and comparative genome analyses of four additional jakobids. Jakobids have mt-rRNA structures that minimally differ from their bacterial counterparts. Yet, with at least 31 small subunit (SSU) and 44 large subunit (LSU) mtRPs, the mitoriboproteome of Andalucia is essentially as complex as that in animals or fungi. Further, the relatively high conservation of jakobid sequences has helped to clarify the identity of several mtRPs, previously considered to be lineage-specific, as divergent homologs of conserved M-mtRPs, notably mS22 and mL61. The coexistence of bacteria-like mt-rRNAs and a complex mitoriboproteome refutes the view that M-mtRPs were ancestrally recruited to stabilize deviations of mt-rRNA structural elements. We postulate instead that the numerous M-mtRPs acquired in the last eukaryotic common ancestor allowed mt-rRNAs to pursue a broad range of evolutionary trajectories across lineages: from dramatic reduction to acquisition of novel elements to structural conservatism.

中文翻译：

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Godyi的一个意想不到的复杂的线粒体，它是一种具有最像细菌的线粒体基因组的生物。

从模型生物的研究中得知，线粒体与它的祖先细菌核糖体有很大不同。偏差包括线粒体核糖体RNA（mt-rRNA）结构的显着减少和许多线粒体特异性（M）线粒体蛋白（mtRPs）的获得。广泛接受的观点认为，M-mtRP可以补偿因其进化重塑而导致的mt-rRNA的结构不稳定。由于有关线粒体构成的大多数实验信息均来自具有衍生的线粒体基因组和mt-rRNA的真核生物，因此我们通过研究jakobids的线粒体翻译机制来检验这一假设。雅各比是一种具有最细菌样线粒体基因组的单细胞蛋白质家。我们在这里报告安达卢西亚godoyi的蛋白质组学分析小的线粒体亚基和计算机转录组学，以及另外四个雅加比虫的比较基因组分析。Jakobids的mt-rRNA结构与其细菌对应物差异最小。然而，至少有31个小亚基（SSU）和44个大亚基（LSU）mtRP，安达卢西亚的线粒体蛋白质组本质上与动物或真菌一样复杂。此外，jakobid序列的相对较高的保守性有助于澄清一些以前被认为是谱系特异性的mtRPs，它们是保守的M-mtRPs的不同同源物，尤其是mS22和mL61。细菌样mt-rRNA和复杂的线粒体蛋白质组的共存，驳斥了M-mtRPs最初被征募来稳定mt-rRNA结构元件偏离的观点。相反，我们假设在上一个真核生物共同祖先中获得的大量M-mtRPs使mt-rRNA沿着谱系追求广泛的进化轨迹：从戏剧性还原到获得新元素再到结构保守。