Human mitochondrial transcripts contain messenger and ribosomal RNAs flanked by transfer RNAs (tRNAs), which are excised by mitochondrial RNase (mtRNase) P and Z to liberate all RNA species. In contrast to nuclear or bacterial RNase P, mtRNase P is not a ribozyme but comprises three protein subunits that carry out RNA cleavage and methylation by unknown mechanisms. Here, we present the cryo-EM structure of human mtRNase P bound to precursor tRNA, which reveals a unique mechanism of substrate recognition and processing. Subunits TRMT10C and SDR5C1 form a subcomplex that binds conserved mitochondrial tRNA elements, including the anticodon loop, and positions the tRNA for methylation. The endonuclease PRORP is recruited and activated through interactions with its PPR and nuclease domains to ensure precise pre-tRNA cleavage. The structure provides the molecular basis for the first step of RNA processing in human mitochondria.

人类线粒体转录物含有侧翼为转移 RNA (tRNA) 的信使 RNA 和核糖体 RNA，它们被线粒体 RNase (mtRNase) P 和 Z 切除以释放所有 RNA 种类。与核或细菌 RNase P 不同，mtRNase P 不是核酶，而是包含三个蛋白质亚基，通过未知机制进行 RNA 切割和甲基化。在这里，我们展示了与前体 tRNA 结合的人 mtRNase P 的冷冻电镜结构，揭示了底物识别和加工的独特机制。TRMT10C 和 SDR5C1 亚基形成一个亚复合体，可结合保守的线粒体 tRNA 元件（包括反密码子环），并定位 tRNA 进行甲基化。核酸内切酶 PRORP 通过与其 PPR 和核酸酶结构域的相互作用来招募和激活，以确保精确的前 tRNA 切割。该结构为人类线粒体中 RNA 加工的第一步提供了分子基础。