H/ACA snR30 snoRNP guides independent 18S rRNA subdomain formation – Dataset 3

Ribosome biogenesis follows a hierarchical set of pre-ribosomal RNA (pre-RNA) folding and processing steps. The earliest, biochemically stable pre-ribosome is the 90S particle, which is assembled co-transcriptionally in the nucleolus. It is unclear how pre-rRNA, ribosomal proteins and assembly factors play together in the early stages of 90S maturation. Is has remained unclear, how the numerous snoRNAs, which guide pre-rRNA modification and folding while the nascent rRNA is flexible and hence accessible, are involved in pre-ribosomal maturation. Here, we identify the conserved C-terminus of assembly factor Krr1 as crucial for efficient release of the essential snR30. Furthermore, we show that snR30 is bound to the central domain of the 18S rRNA within a complex that contains assembly factors and ribosomal proteins. Our study shows how independent 18S domain maturation is guided by snR30 in coupling rRNA chaperoning with the delivery of ribosomal proteins.

核糖体生物发生遵循一套层级化的核糖体前体RNA（pre-ribosomal RNA，pre-RNA）折叠与加工流程。最早且生化性质稳定的核糖体前体颗粒为90S颗粒，其在核仁中通过共转录方式完成组装。目前学界仍未明确，在90S颗粒成熟的早期阶段，核糖体前体RNA、核糖体蛋白与组装因子之间如何协同发挥功能。同样悬而未决的问题还有：众多在新生rRNA处于柔性状态、易于被靶向结合时引导其修饰与折叠的核仁小RNA（small nucleolar RNAs，snoRNAs），是如何参与核糖体前体的成熟过程的。本研究鉴定出组装因子Krr1的保守C端结构域对于必需snR30的有效释放至关重要。此外，我们证实snR30结合于包含组装因子与核糖体蛋白的复合物内的18S核糖体RNA（18S rRNA）中心结构域。本研究阐明了snR30如何介导独立的18S结构域成熟过程，将RNA分子伴侣活性与核糖体蛋白的递送过程相偶联。