Molecular architecture of the 90S small subunit pre-ribosome

作者：Qi Sun, Xing Zhu, Jia Qi, Weidong An, Pengfei Lan, Dan Tan, Rongchang Chen, Bing Wang, Sanduo Zheng, Cheng Zhang, Xining Chen, Wei Zhang, Jing Chen, Meng‐Qiu Dong, Keqiong Ye · 发表于：eLife · 年份：2017 · DOI：10.7554/elife.22086 · 被引用次数：155 · 研究领域：RNA modifications and cancer、RNA and protein synthesis mechanisms、RNA Research and Splicing

Eukaryotic small ribosomal subunits are first assembled into 90S pre-ribosomes. The complete 90S is a gigantic complex with a molecular mass of approximately five megadaltons. Here, we report the nearly complete architecture of Saccharomyces cerevisiae 90S determined from three cryo-electron microscopy single particle reconstructions at 4.5 to 8.7 angstrom resolution. The majority of the density maps were modeled and assigned to specific RNA and protein components. The nascent ribosome is assembled into isolated native-like substructures that are stabilized by abundant assembly factors. The 5' external transcribed spacer and U3 snoRNA nucleate a large subcomplex that scaffolds the nascent ribosome. U3 binds four sites of pre-rRNA, including a novel site on helix 27 but not the 3' side of the central pseudoknot, and crucially organizes the 90S structure. The 90S model provides significant insight into the principle of small subunit assembly and the function of assembly factors.