Alberta RNA Research and Training Institute (ARRTI), Department of Chemistry & Biochemistry, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada.
Cells. 2020 Sep 29;9(10):2195. doi: 10.3390/cells9102195.
The small nucleolar RNA snR30 (U17 in humans) plays a unique role during ribosome synthesis. Unlike most members of the H/ACA class of guide RNAs, the small nucleolar ribonucleoprotein (snoRNP) complex assembled on snR30 does not direct pseudouridylation of ribosomal RNA (rRNA), but instead snR30 is critical for 18S rRNA processing during formation of the small subunit (SSU) of the ribosome. Specifically, snR30 is essential for three pre-rRNA cleavages at the A/01, A/1, and A/2a sites in yeast and humans, respectively. Accordingly, snR30 is the only essential H/ACA guide RNA in yeast. Here, we summarize our current knowledge about the interactions and functions of snR30, discuss what remains to be elucidated, and present two non-exclusive hypotheses on the possible molecular function of snR30 during ribosome biogenesis. First, snR30 might be responsible for recruiting other proteins including endonucleases to the SSU processome. Second, snR30 may contribute to the refolding of pre-rRNA into a required conformation that serves as a checkpoint during ribosome biogenesis facilitating pre-rRNA cleavage. In both scenarios, the snR30 snoRNP may have scaffolding and RNA chaperoning activity. In conclusion, the snR30 snoRNP is a crucial player with an unknown molecular mechanism during ribosome synthesis, posing many interesting future research questions.
小核仁 RNA snR30（人类中的 U17）在核糖体合成过程中发挥独特作用。与大多数 H/ACA 类向导 RNA 不同，组装在 snR30 上的小核仁核糖核蛋白 (snoRNP) 复合物不指导核糖体 RNA（rRNA）的假尿嘧啶化，而是 snR30 对于核糖体小亚基 (SSU) 形成过程中的 18S rRNA 加工至关重要。具体而言，snR30 分别在酵母和人类中对于 pre-rRNA 在 A/01、A/1 和 A/2a 位点的三个切割是必需的。因此，snR30 是酵母中唯一必需的 H/ACA 向导 RNA。在这里，我们总结了我们目前对 snR30 相互作用和功能的了解，讨论了仍需阐明的问题，并提出了 snR30 在核糖体生物发生过程中可能的分子功能的两个非排他性假设。首先，snR30 可能负责将其他蛋白质（包括内切核酸酶）招募到 SSU 加工体。其次，snR30 可能有助于 pre-rRNA 重新折叠成所需构象，该构象在核糖体生物发生过程中作为检查点，促进 pre-rRNA 切割。在这两种情况下，snR30 snoRNP 可能具有支架和 RNA 伴侣活性。总之，snR30 snoRNP 是核糖体合成过程中具有未知分子机制的关键参与者，提出了许多有趣的未来研究问题。
