Molecular, Cellular and Developmental Biology department (MCD), Centre de Biologie Integrative (CBI), University of Toulouse, CNRS, UPS, Toulouse, France.
Institut für Biochemie, ETH Zürich, Zurich, Switzerland.
Elife. 2021 Apr 28;10:e61254. doi: 10.7554/eLife.61254.
Preventing premature interaction of pre-ribosomes with the translation apparatus is essential for translational accuracy. Hence, the final maturation step releasing functional 40S ribosomal subunits, namely processing of the 18S ribosomal RNA 3' end, is safeguarded by the protein DIM2, which both interacts with the endoribonuclease NOB1 and masks the rRNA cleavage site. To elucidate the control mechanism that unlocks NOB1 activity, we performed cryo-electron microscopy analysis of late human pre-40S particles purified using a catalytically inactive form of the ATPase RIO1. These structures, together with in vivo and in vitro functional analyses, support a model in which ATP-loaded RIO1 cooperates with ribosomal protein RPS26/eS26 to displace DIM2 from the 18S rRNA 3' end, thereby triggering final cleavage by NOB1; release of ADP then leads to RIO1 dissociation from the 40S subunit. This dual key lock mechanism requiring RIO1 and RPS26 guarantees the precise timing of pre-40S particle conversion into translation-competent ribosomal subunits.
防止前核糖体过早与翻译装置相互作用对于翻译准确性至关重要。因此，释放功能性 40S 核糖体亚基的最后成熟步骤，即 18S 核糖体 RNA 3' 端的加工，由蛋白质 DIM2 保护，它既与内切核酸酶 NOB1 相互作用，又掩盖 rRNA 切割位点。为了阐明解锁 NOB1 活性的控制机制，我们使用催化无活性形式的 ATP 酶 RIO1 纯化的晚期人前 40S 颗粒进行了低温电子显微镜分析。这些结构以及体内和体外功能分析支持了一个模型，即加载 ATP 的 RIO1 与核糖体蛋白 RPS26/eS26 合作，将 DIM2 从 18S rRNA 3' 端置换，从而触发 NOB1 的最终切割；然后 ADP 的释放导致 RIO1 从 40S 亚基解离。这种需要 RIO1 和 RPS26 的双重关键锁机制保证了前 40S 颗粒转化为具有翻译能力的核糖体亚基的精确时间。
