Hamze Hussein, Jaafar Mariam, Khreiss Ali, Dominique Carine, Bourdeaux Jessie, Santo Paulo Espirito, Méndez-Godoy Alfonso, Kressler Dieter, Humbert Odile, Plisson-Chastang Célia, Albert Benjamin, Henras Anthony K, Henry Yves
Molecular, Cellular and Developmental Biology Unit (MCD), Centre de Biologie Intégrative (CBI), Université de Toulouse, CNRS, 31062 Toulouse, France.
Department of Biology, University of Fribourg, Chemin du Musée 10, 1700 Fribourg, Switzerland.
Nucleic Acids Res. 2025 Feb 27;53(5). doi: 10.1093/nar/gkaf134.
The early steps of large-ribosomal-subunit assembly feature among the least understood steps of ribosome synthesis in eukaryotes. In Saccharomyces cerevisiae, the box C/D chaperone small nucleolar ribonucleoprotein (snoRNP) snR190 and the Npa1 complex, composed of the α-solenoid scaffold proteins Npa1 and Npa2, the DEAD-box helicase Dbp6, the RNA-binding protein Nop8, and Rsa3, are likely involved in early 25S ribosomal RNA (rRNA) folding events. Here, we report for the first time the existence outside pre-ribosomal particles of an independent macromolecular assembly constituted by the Npa1 complex and the chaperone snoRNP snR190. Nop8 mediates the formation of this assembly and can associate on its own with free snR190 snoRNP. Moreover, Nop8 RNA Recognition Motif (RRM) helps tether the snR190 snoRNP to pre-ribosomal particles. The snR190 snoRNA features a specific central stem-loop structure, which is required for high-affinity binding between free snR190 snoRNP and the Npa1 complex. Deleting this extension does not prevent snR190 snoRNA association with pre-ribosomal particles but impairs snR190 activity in early pre-rRNA processing events. This work establishes the importance of association with auxiliary protein complexes for optimum snoRNP chaperone activity during rRNA folding events.
在真核生物核糖体合成过程中，大核糖体亚基组装的早期步骤是了解最少的步骤之一。在酿酒酵母中，C/D盒分子伴侣小核仁核糖核蛋白（snoRNP）snR190和由α-螺线管支架蛋白Npa1和Npa2、DEAD盒解旋酶Dbp6、RNA结合蛋白Nop8以及Rsa3组成的Npa1复合物，可能参与早期25S核糖体RNA（rRNA）折叠事件。在此，我们首次报道了由Npa1复合物和分子伴侣snoRNP snR190构成的独立大分子组装体存在于核糖体前体颗粒之外。Nop8介导了该组装体的形成，并且自身可与游离的snR190 snoRNP结合。此外，Nop8的RNA识别基序（RRM）有助于将snR190 snoRNP连接到核糖体前体颗粒上。snR190 snoRNA具有特定的中央茎环结构，这是游离的snR190 snoRNP与Npa1复合物之间高亲和力结合所必需的。删除该延伸部分并不妨碍snR190 snoRNA与核糖体前体颗粒的结合，但会损害snR190在早期前体rRNA加工事件中的活性。这项工作确立了在rRNA折叠事件中，与辅助蛋白复合物结合对于snoRNP分子伴侣最佳活性的重要性。
