Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Nucleic Acids Res. 2023 Nov 10;51(20):10867-10883. doi: 10.1093/nar/gkac430.
During eukaryotic ribosome biogenesis, pre-ribosomes travel from the nucleolus, where assembly is initiated, to the nucleoplasm and then are exported to the cytoplasm, where assembly concludes. Although nuclear export of pre-ribosomes has been extensively investigated, the release of pre-ribosomes from the nucleolus is an understudied phenomenon. Initial data indicate that unfolded rRNA interacts in trans with nucleolar components and that, when rRNA folds due to ribosomal protein (RP) binding, the number of trans interactions drops below the threshold necessary for nucleolar retention. To validate and expand on this idea, we performed a bioinformatic analysis of the protein components of the Saccharomyces cerevisiae ribosome assembly pathway. We found that ribosome biogenesis factors (RiBi factors) contain significantly more predicted trans interacting regions than RPs. We also analyzed cryo-EM structures of ribosome assembly intermediates to determine how nucleolar pre-ribosomes differ from post-nucleolar pre-ribosomes, specifically the capacity of RPs, RiBi factors, and rRNA components to interact in trans. We observed a significant decrease in the theoretical trans-interacting capability of pre-ribosomes between nucleolar and post-nucleolar stages of assembly due to the release of RiBi factors from particles and the folding of rRNA. Here, we provide a mechanism for the release of pre-ribosomes from the nucleolus.
在真核生物核糖体生物发生过程中，前核糖体从起始组装的核仁中移动到核质，然后输出到细胞质中完成组装。尽管前核糖体的核输出已经得到了广泛的研究，但前核糖体从核仁中的释放仍然是一个研究较少的现象。初步数据表明，未折叠的 rRNA 与核仁成分发生反式相互作用，并且当 rRNA 由于核糖体蛋白 (RP) 结合而折叠时，反式相互作用的数量下降到低于核仁保留所需的阈值。为了验证和扩展这一观点，我们对酿酒酵母核糖体组装途径的蛋白质成分进行了生物信息学分析。我们发现，核糖体生物发生因子 (RiBi 因子) 比 RP 包含更多预测的反式相互作用区域。我们还分析了核糖体组装中间产物的冷冻电镜结构，以确定核仁前核糖体与核后前核糖体有何不同，特别是 RP、RiBi 因子和 rRNA 成分反式相互作用的能力。我们观察到，由于 RiBi 因子从颗粒中释放以及 rRNA 的折叠，组装的核仁与核后阶段之间前核糖体的理论反式相互作用能力显著下降。在这里，我们提供了前核糖体从核仁中释放的机制。
