Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Nucleic Acids Res. 2012 Sep 1;40(17):8646-61. doi: 10.1093/nar/gks609. Epub 2012 Jun 26.
To better define the roles of assembly factors required for eukaryotic ribosome biogenesis, we have focused on one specific step in maturation of yeast 60 S ribosomal subunits: processing of 27SB pre-ribosomal RNA. At least 14 assembly factors, the 'B-factor' proteins, are required for this step. These include most of the major functional classes of assembly factors: RNA-binding proteins, scaffolding protein, DEAD-box ATPases and GTPases. We have investigated the mechanisms by which these factors associate with assembling ribosomes. Our data establish a recruitment model in which assembly of the B-factors into nascent ribosomes ultimately leads to the recruitment of the GTPase Nog2. A more detailed analysis suggests that this occurs in a hierarchical manner via two largely independent recruiting pathways that converge on Nog2. Understanding recruitment has allowed us to better determine the order of association of all assembly factors functioning in one step of ribosome assembly. Furthermore, we have identified a novel subcomplex composed of the B-factors Nop2 and Nip7. Finally, we identified a means by which this step in ribosome biogenesis is regulated in concert with cell growth via the TOR protein kinase pathway. Inhibition of TOR kinase decreases association of Rpf2, Spb4, Nog1 and Nog2 with pre-ribosomes.
为了更好地定义真核生物核糖体生物发生所需的组装因子的作用，我们专注于酵母 60S 核糖体亚基成熟的一个特定步骤：27SB 前核糖体 RNA 的加工。至少有 14 个组装因子，即“B 因子”蛋白，是这一步所必需的。这些因子包括大多数主要的组装因子功能类别：RNA 结合蛋白、支架蛋白、DEAD 盒 ATP 酶和 GTP 酶。我们研究了这些因子与正在组装的核糖体结合的机制。我们的数据建立了一个招募模型，其中 B 因子组装到新生核糖体中，最终导致 GTPase Nog2 的招募。更详细的分析表明，这是通过两种基本上独立的招募途径以级联方式发生的，这两种途径都汇聚在 Nog2 上。对招募机制的理解使我们能够更好地确定在核糖体组装的一个步骤中所有组装因子的关联顺序。此外，我们还鉴定了一个由 B 因子 Nop2 和 Nip7 组成的新亚基。最后，我们确定了一种通过 TOR 蛋白激酶途径与细胞生长协调调节核糖体生物发生这一步骤的方法。TOR 激酶的抑制会减少 Rpf2、Spb4、Nog1 和 Nog2 与前核糖体的结合。
