Dynamic conformational model for the role of ITS2 in pre-rRNA processing in yeast
Dynamic conformational model for the role of ITS2 in pre-rRNA processing in yeast
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DOI：
10.1017/s1355838202023063
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发表时间：
2002-06-01
期刊：
影响因子：
4.5
通讯作者：
Peculis, BA
中科院分区：
文献类型：
--
作者：
Côte, CA;Greer, CL;Peculis, BA
大亚基rRNA的成熟包括一系列裂解，导致分离成熟5.8S和25/28 S rRNA的内部转录间隔区（ITS 2）的去除。先前的工作表明，在组装的前核糖体颗粒内形成高级二级结构是准确和有效的前rRNA加工的先决条件。迄今为止，尚不清楚加工需要哪些特定序列或二级结构。酿酒酵母ITS 2存在两种替代的二级结构模型。化学和酶结构探测和系统发育比较产生一种结构（Yeh & Lee，J Mol Biol，1990，211：699-712），在此称为“发夹模型”。最近，提出了一种替代的折叠结构（Joseph等人，Nucleic Acids Res，1999，27：4533-4540），在此称为“环模型”。“我们已经使用了一种功能性遗传分析来研究这些预测结构在加工过程中的潜在意义。我们的数据表明，这两种结构模型的元素是重要的有效处理。阻止环特异性结构形成的突变完全阻断了成熟25 S rRNA的产生，而那些主要破坏发夹元件的突变导致成熟产物水平降低。基于这些结果，我们提出了一个动态的构象模型ITS 2在加工中的作用：初始形成的环结构可能是必需的，早期事件在处理复杂的组装，并可能随后诱导过渡到发夹结构，促进后续的处理事件。在该模型中，酵母ITS 2元件可以顺式提供针对反式作用的脊椎动物U8 snoRNA提出的某些功能。
Maturation of the large subunit rRNAs includes a series of cleavages that result in removal of the internal transcribed spacer (ITS2) that separates mature 5.8S and 25/28S rRNAs. Previous work demonstrated that formation of higher order secondary structure within the assembling pre-ribosomal particle is a prerequisite for accurate and efficient pre-rRNA processing. To date, it is not clear which specific sequences or secondary structures are required for processing. Two alternative secondary structure models exist for Saccharomyces cerevisiae ITS2. Chemical and enzymatic structure probing and phylogenetic comparisons resulted in one structure (Yeh & Lee, J Mol Biol, 1990, 211:699-712) referred to here as the "hairpin model." More recently, an alternate folded structure was proposed (Joseph et al., Nucleic Acids Res, 1999, 27:4533-4540), called here the "ring model." We have used a functional genetic assay to examine the potential significance of these predicted structures in processing. Our data indicate that elements of both structural models are important in efficient processing. Mutations that prevent formation of ring-specific structures completely blocked production of mature 25S rRNA, whereas those that primarily disrupt hairpin elements resulted in reduced levels of mature product. Based on these results, we propose a dynamic conformational model for the role of ITS2 in processing: Initial formation of the ring structure may be required for essential, early events in processing complex assembly and may be followed by an induced transition to the hairpin structure that facilitates subsequent processing events. In this model, yeast ITS2 elements may provide in cis certain of the functions proposed for vertebrate U8 snoRNA acting In trans.