Expression Génétique Microbienne, UMR 8261, CNRS, Université de Paris, Institut de Biologie Physico-Chimique (IBPC), 75005 Paris, France.
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK.
Mol Cell. 2020 Oct 15;80(2):227-236.e5. doi: 10.1016/j.molcel.2020.09.008. Epub 2020 Sep 28.
The pathways for ribosomal RNA (rRNA) maturation diverge greatly among the domains of life. In the Gram-positive model bacterium, Bacillus subtilis, the final maturation steps of the two large ribosomal subunit (50S) rRNAs, 23S and 5S pre-rRNAs, are catalyzed by the double-strand specific ribonucleases (RNases) Mini-RNase III and RNase M5, respectively. Here we present a protocol that allowed us to solve the 3.0 and 3.1 Å resolution cryoelectron microscopy structures of these RNases poised to cleave their pre-rRNA substrates within the B. subtilis 50S particle. These data provide the first structural insights into rRNA maturation in bacteria by revealing how these RNases recognize and process double-stranded pre-rRNA. Our structures further uncover how specific ribosomal proteins act as chaperones to correctly fold the pre-rRNA substrates and, for Mini-III, anchor the RNase to the ribosome. These r-proteins thereby serve a quality-control function in the process from accurate ribosome assembly to rRNA processing.
核糖体 RNA（rRNA）成熟的途径在生命的各个领域有很大的不同。在革兰氏阳性模式细菌枯草芽孢杆菌中，两个大亚基（50S）rRNA 的 23S 和 5S 前 rRNA 的最终成熟步骤分别由双链特异性核糖核酸酶（RNase）Mini-RNase III 和 RNase M5 催化。在这里，我们提供了一个方案，使我们能够解决这两种 RNase 处于切割其前 rRNA 底物的状态下的 3.0 和 3.1Å 分辨率冷冻电子显微镜结构，这些 RNase 位于枯草芽孢杆菌 50S 颗粒内。这些数据通过揭示这些 RNase 如何识别和加工双链前 rRNA，为细菌中的 rRNA 成熟提供了第一个结构见解。我们的结构进一步揭示了特定的核糖体蛋白如何作为伴侣蛋白正确折叠前 rRNA 底物，并且对于 Mini-III，将 RNase 锚定在核糖体上。这些 r 蛋白在从核糖体组装到 rRNA 加工的精确过程中充当质量控制功能。
