Biogenesis of the Small Ribosomal Subunit in Eukaryotes

所有细胞都需要核糖体进行翻译，即解码信使的过程 RNA和合成蛋白质。为了满足快速分割的平移需求， 在真核细胞中，在一个过程中每分钟必须合成数千个核糖体。 消耗了细胞能量预算的很大一部分。事实上， 许多癌症需要核糖体生物合成的上调。因此，理解 调节核糖体生物发生的机制将为开发 控制疾病状态下细胞增殖的新工具。划定 基本的细胞途径，如核糖体生物合成，也是建立 翻译研究的知识基础。 真核生物核糖体生物合成的许多基本步骤 明白我们的功能遗传学方法（约翰逊实验室）结合了 体外生物化学模型（Correll实验室）的发展使我们处于一个特别强大的 研究真核生物核糖体生物发生的一个基本步骤;过渡 从前核糖体颗粒（90 S）到前40 S颗粒（小亚基前体）。 我们的总体模型是甲基转移酶Bud 23监测40 S的状态， 组装，触发RNA解旋酶Ecm 16以促进前40 S从 90 S仅在完成转录和RNA的关键折叠之后。一个主要 在我们的初步结果的成就是我们的能力，捕获一个Ecm 16-中间体 粒子为了开始解决这个模型，我们的研究测试了四个具体的假设：（i） Ecm 16是解旋酶，其将U3 snoRNA及其相关蛋白从细胞中解离。 （ii）Bud 23激活这种解旋酶活性;（iii）Imp 4稳定双链体， Ecm 16的靶标;和（iv）Ecm 16的核糖体蛋白Rps 2伴侣蛋白的形成。 中央假结，18 S rRNA的一个关键结构特征，其形成是空间上的， 阻断直至Ecm 16破坏U3-pre-rRNA相互作用。前rRNA加工 在酿酒酵母中要研究的途径和基因有 高等真核生物中的对应物。因此，S。酿酒酵母是我们选择的模式生物 因为它使我们能够联合收割机将强大的分子遗传学和生物化学 方法。

All cells require ribosomes for translation, the process of decoding messenger RNA and synthesizing proteins. To satisfy the translational needs of a rapidly dividing eukaryotic cell, thousands of ribosomes must be synthesized per minute in a process that consumes a large portion of the cell's energy budget. Indeed, the rapid growth of many cancers requires up-regulation of ribosome biogenesis. Thus, understanding the mechanisms regulating ribosome biogenesis will provide insight for the development of new tools for controlling cell proliferation in disease states. The delineation of fundamental cellular pathways such as ribosome biogenesis is also critical for building the intellectual foundation for translational research. Many of the fundamental steps of eukaryotic ribosome biogenesis are poorly understood. Our functional genetic approach (Johnson lab) combined with the development of in vitro biochemical models (Correll lab) places us in a particularly strong position to study a fundamental step in eukaryotic ribosome biogenesis; the transition from the pre-ribosome particle (90S) to the pre-40S particle (small subunit precursor). Our overarching model is that the methyltransferase Bud23 monitors that status of 40S assembly, triggering the RNA helicase Ecm16 to promote release of the pre-40S from 90S only after completion of transcription and critical folding of the RNA. A major achievement in our preliminary results is our ability to trap an Ecm16-intermediate particle. To begin to address this model, our studies test four specific hypotheses: (i) Ecm16 is the helicase that dissociates U3 snoRNA and its associated proteins from the pre-rRNA (ii) Bud23 activates this helicase activity; (iii) Imp4 stabilizes the duplex that is the target of Ecm16; and (iv) the ribosomal protein Rps2 chaperones formation of the central pseudoknot, a key structural feature in 18S rRNA whose formation is sterically blocked until Ecm16 disrupts the U3-pre-rRNA interactions. The pre-rRNA processing pathways and the genes to be studied in the yeast Saccharomyces cerevisiae have counterparts in higher eukaryotes. Hence, S. cerevisiae is our model organism of choice because it allows us to combine powerful molecular genetic and biochemical approaches.