Mammalian mitochondrial ribosomes (mitoribosomes) have less rRNA content and 36 additional proteins compared with the evolutionarily related bacterial ribosome. These differences make the assembly of mitoribosomes more complex than the assembly of bacterial ribosomes, but the molecular details of mitoribosomal biogenesis remain elusive. Here, we report the structures of two late-stage assembly intermediates of the human mitoribosomal large subunit (mt-LSU) isolated from a native pool within a human cell line and solved by cryo-EM to ~3-Å resolution. Comparison of the structures reveals insights into the timing of rRNA folding and protein incorporation during the final steps of ribosomal maturation and the evolutionary adaptations that are required to preserve biogenesis after the structural diversification of mitoribosomes. Furthermore, the structures redefine the ribosome silencing factor (RsfS) family as multifunctional biogenesis factors and identify two new assembly factors (L0R8F8 and mt-ACP) not previously implicated in mitoribosomal biogenesis.

中文翻译：

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人类线粒体核糖体的天然组装状态结构。

与进化相关的细菌核糖体相比，哺乳动物的线粒体核糖体（线粒体）具有更少的rRNA含量和36种其他蛋白质。这些差异使得线粒体的组装比细菌核糖体的组装更为复杂，但是线粒体生物发生的分子细节仍然难以捉摸。在这里，我们报告了人类线粒体大亚基（mt-LSU）的两个后期组装中间体的结构，这些中间体是从人类细胞系的天然库中分离出来的，并通过冷冻EM解析为〜3-Å的分辨率。结构的比较揭示了核糖体成熟的最后步骤中rRNA折叠和蛋白质掺入的时间以及有丝分裂体结构多样化后保留生物发生所需的进化适应的见解。此外，