Assembly of eukaryotic ribosomal subunits is a complex and dynamic process involving the action of more than 200 trans-acting assembly factors. Although recent cryo-electron microscopy structures have provided information on architecture of several pre-ribosomal particles and the binding sites of many AFs, the RNA and protein interactions of many other AFs not captured in these snapshots still remain elusive. RNA helicases are key regulators of structural rearrangements within pre-ribosomal complexes and here we have analysed the eIF4A-like RNA helicase Fal1 and its putative cofactor Sgd1. Our data show that these proteins interact directly via the MIF4G domain of Sgd1 and that the MIF4G domain of Sgd1 stimulates the catalytic activity of Fal1 in vitro. The catalytic activity of Fal1, and the interaction between Fal1 and Sgd1, are required for efficient pre-rRNA processing at the A0, A1 and A2 sites. Furthermore, Sgd1 co-purifies the early small subunit biogenesis factors Lcp5 and Rok1, suggesting that the Fal1-Sgd1 complex likely functions within the SSU processome. In vivo crosslinking data reveal that Sgd1 binds to helix H12 of the 18S rRNA sequence and we further demonstrate that this interaction is formed by the C-terminal region of the protein, which is essential for its function in ribosome biogenesis.

中文翻译：

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Sgd1是RNA解旋酶Fal1的含MIF4G域的辅因子，与18S rRNA序列的5'域结合。

真核生物核糖体亚基的组装是一个复杂而动态的过程，涉及200多个反式组装因子的作用。尽管最近的低温电子显微镜结构已经提供了有关几个核糖体前颗粒的结构以及许多AF的结合位点的信息，但是在这些快照中未捕获的许多其他AF的RNA和蛋白质相互作用仍然难以捉摸。RNA解旋酶是核糖体前复合物中结构重排的关键调控因子，在这里我们分析了eIF4A样RNA解旋酶Fal1及其推定的辅助因子Sgd1。我们的数据表明，这些蛋白质通过Sgd1的MIF4G结构域直接相互作用，而Sgd1的MIF4G结构域在体外刺激Fal1的催化活性。Fal1的催化活性以及Fal1和Sgd1之间的相互作用，是在A0，A1和A2位点进行高效rRNA预处理所必需的。此外，Sgd1共纯化早期的小亚基生物发生因子Lcp5和Rok1，表明Fal1-Sgd1复合物可能在SSU进程组内起作用。体内交联数据显示Sgd1与18S rRNA序列的螺旋H12结合，并且我们进一步证明了这种相互作用是由蛋白质的C端区域形成的，这对于其在核糖体生物发生中的功能至关重要。