RNA helicases play various roles in ribosome biogenesis depending on the ribosome assembly pathway and stress state of the cell. However, it is unclear how most RNA helicases interact with ribosome assembly intermediates or participate in other cell processes to regulate ribosome assembly. SrmB is a DEAD-box helicase that acts early in the ribosome assembly process, although very little is known about its mechanism of action. Here, we use a combined quantitative mass spectrometry/cryo-electron microscopy approach to detail the protein inventory, rRNA modification state, and structures of 40S ribosomal intermediates that form upon SrmB deletion. We show that the binding site of SrmB is unperturbed by SrmB deletion, but the peptidyl transferase center, the uL7/12 stalk, and 30S contact sites all show severe assembly defects. Taking into account existing data on SrmB function and the experiments presented here, we propose several mechanisms by which SrmB could guide assembling particles from kinetic traps to competent subunits during the 50S ribosome assembly process.

中文翻译：

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SrmB救援被困的核糖体组装中间体。

RNA解旋酶在核糖体生物发生中扮演各种角色，具体取决于核糖体装配途径和细胞的应激状态。但是，目前尚不清楚大多数RNA解旋酶如何与核糖体装配中间体相互作用或如何参与其他细胞过程来调节核糖体装配。SrmB是一种DEAD-box解旋酶，在核糖体组装过程中起早期作用，尽管对其作用机理知之甚少。在这里，我们使用定量质谱/冷冻电子显微镜相结合的方法来详细说明蛋白质清单，rRNA修饰状态以及在SrmB缺失后形成的40S核糖体中间体的结构。我们显示SrmB的结合位点不受SrmB缺失的干扰，但肽基转移酶中心，uL7 / 12茎和30S接触位点均显示严重的装配缺陷。