How ribosomes are made The formation of eukaryotic ribosomes is a complex process that starts with transcription of a large precursor RNA that assembles into a large 90S preribosome, which matures to finally give the 40S small subunit of the ribosome. Cheng et al. and Du et al. give insight into this process, using cryo–electron microscopy to look at intermediates along the pathway. Together, these studies reveal how a cast of molecular players act to coordinate the compositional and structural changes that transform the 90S preribosome into a pre-40S subunit. Science, this issue p. 1470, p. 1477 The steps the steps that drive the stepwise dissociation of factors in the transition from the 90S to the 40S ribosome subunit are observed. The 90S preribosome is a large, early assembly intermediate of small ribosomal subunits that undergoes structural changes to give a pre-40S ribosome. Here, we gained insight into this transition by determining cryo–electron microscopy structures of Saccharomyces cerevisiae intermediates in the path from the 90S to the pre-40S. The full transition is blocked by deletion of RNA helicase Dhr1. A series of structural snapshots revealed that the excised 5′ external transcribed spacer (5′ ETS) is degraded within 90S, driving stepwise disassembly of assembly factors and ribosome maturation. The nuclear exosome, an RNA degradation machine, docks on the 90S through helicase Mtr4 and is primed to digest the 3′ end of the 5′ ETS. The structures resolved between 3.2- and 8.6-angstrom resolution reveal key intermediates and the critical role of 5′ ETS degradation in 90S progression.

中文翻译：

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过渡态 90S 小核糖体亚基前体的冷冻电镜结构

核糖体是如何制造的 真核生物核糖体的形成是一个复杂的过程，从一个大的前体 RNA 的转录开始，该前体 RNA 组装成一个大的 90S 前核糖体，它成熟最终形成核糖体的 40S 小亚基。程等人。和杜等人。深入了解这个过程，使用冷冻电子显微镜观察沿途的中间体。总之，这些研究揭示了一系列分子参与者如何协调将 90S 前核糖体转变为 40S 前亚基的组成和结构变化。科学，这个问题 p。1470 页。1477 在从 90S 到 40S 核糖体亚基的转变过程中，驱动因子逐步解离的步骤被观察到。90S 前核糖体是一个大的，小核糖体亚基的早期组装中间体，经过结构变化以产生前 40S 核糖体。在这里，我们通过确定从 90 年代到 40 年代之前的路径中酿酒酵母中间体的冷冻电子显微镜结构，深入了解了这种转变。通过删除 RNA 解旋酶 Dhr1 来阻止完全转变。一系列结构快照显示，切除的 5' 外部转录间隔区 (5' ETS) 在 90 秒内降解，推动组装因子的逐步分解和核糖体成熟。核外泌体是一种 RNA 降解机器，通过解旋酶 Mtr4 停靠在 90S 上，并准备消化 5' ETS 的 3' 末端。在 3.2 和 8.6 埃分辨率之间解析的结构揭示了关键中间体和 5' ETS 降解在 90S 进程中的关键作用。