Role of Accessory Proteins P50/P55 in SnoRNP Biogenesis

核仁小RNA(SnoRNAs)在真核生物核糖体生物合成中起着至关重要的作用。关键的snoRNA功能包括指导核糖体前RNA前体的切割和指导核糖体RNA中特定核苷酸的修饰。已在核仁中鉴定出100多个snoRNAs，从而确立了snoRNAs是真核细胞中发现的最大的一类小而稳定的RNAs。研究表明，box C/D和H/ACA snoRNAs具有各自家族特有的进化保守序列和折叠结构。每个RNA基序都与家族特异性蛋白质结合，建立snoRNA：蛋白质(SnoRNP)复合体。盒C/D和H/ACA snoRNA基序及其相关的核心蛋白都是snoRNA加工、snoRNP运输和snoRNA引导的核糖体RNA核苷酸修饰所必需的。最近，两种新的辅助蛋白被鉴定出来，它们也是snoRNP合成所必需的。辅助蛋白p50和p55与核质中的snoRNP核心复合体相互作用，调节snoRNP的产生。尽管p50/p55在合成新的snoRNP复合体中起重要作用，但目前还不清楚它们是如何发挥作用的。因此，本研究的目的是双重的。首先，我们将在非洲爪哇卵母细胞核中研究p50/p55‘S在snoRNP生物发生中的作用。显微注射实验将确定这些辅助蛋白在核质中组装snoRNP的可能作用，以及它们在将成熟的snoRNP复合体运输到核仁中的潜在功能。其次，结构研究将定义p50/p55与box C/D核心snoRNP复合体的相互作用，提供调节snoRNP生物合成途径的辅助蛋白功能的机制细节。P50和P55是第一个被发现的snoRNP辅助蛋白，是snoRNP生物合成所必需的。确定它们的功能角色将为深入了解snoRNA/snoRNP生物合成途径提供基础。P50/p55参与了其他核质事件，如染色质重塑和RNA合成，这表明p50和p55是一种多功能蛋白质，可能是协调真核细胞中各种过程的分子桥梁。因此，这项研究有可能影响我们对真核细胞核内RNA代谢的基本理解，并揭示新的基因表达调控范式。

The small nucleolar RNAs (snoRNAs) play essential roles in eukaryotic ribosome biosynthesis. Critical snoRNA functions include directing cleavage of the pre-ribosomal RNA precursor and guiding the modification of specific nucleotides in the ribosomal RNAs. More than 100 snoRNAs have been identified in the nucleolus, thus establishing the snoRNAs as the largest class of small stable RNAs found in eukaryotic cells. Investigations have demonstrated that the box C/D and H/ACA snoRNAs exhibit evolutionarily conserved sequences and folded structures characteristic of each family. Each of these RNA motifs bind family-specific proteins to establish the snoRNA:protein (snoRNP) complex. Both the box C/D and H/ACA snoRNA motifs and their associated core proteins are required for snoRNA processing, snoRNP transport, and snoRNA-guided nucleotide modification of ribosomal RNAs. Most recently, two novel accessory proteins have been identified that are also essential for snoRNP synthesis. Accessory proteins p50 and p55 interact with the snoRNP core complex in the nucleoplasm and regulate snoRNP production. Despite their critical nature, nothing is yet known about how p50/p55 function in the synthesis of new snoRNP complexes. Therefore, the goals of this research are twofold. First, p50/p55's role in snoRNP biogenesis will be examined in vivo in the Xenopus oocyte nucleus. Microinjection experiments will determine the possible role of these accessory proteins for snoRNP assembly in the nucleoplasm as well as their potential function in transporting mature snoRNP complexes into the nucleolus. Second, structural studies will define the interactions of p50/p55 with the box C/D core snoRNP complex, providing mechanistic details of accessory protein function in regulating the snoRNP biosynthetic pathway. p50 and p55 are the first identified snoRNP accessory proteins essential for snoRNP biosynthesis. Defining their functional roles will provide fundamental insight into the snoRNA/snoRNP biosynthetic pathway. The involvement of p50/p55 in other nucleoplasmic events such as chromatin remodeling and RNA synthesis has suggested that p50 and p55 are multifunctional proteins and may serve as "molecular bridges" to coordinate various processes in the eukaryotic nucleus. Therefore, this research has the potential to impact our basic understanding of RNA metabolism in the eukaryotic nucleus and reveal new regulatory paradigms of gene expression.