THE TERMINAL BALLS CHARACTERISTIC OF EUKARYOTIC RIBOSOMAL-RNA TRANSCRIPTION UNITS IN CHROMATIN SPREADS ARE RIBOSOMAL-RNA PROCESSING COMPLEXES
THE TERMINAL BALLS CHARACTERISTIC OF EUKARYOTIC RIBOSOMAL-RNA TRANSCRIPTION UNITS IN CHROMATIN SPREADS ARE RIBOSOMAL-RNA PROCESSING COMPLEXES
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DOI：
10.1101/gad.7.8.1609
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发表时间：
1993-08-01
影响因子：
10.5
通讯作者：
SOLLNERWEBB, B
中科院分区：
文献类型：
--
作者：
MOUGEY, EB;OREILLY, M;SOLLNERWEBB, B
当通过电子显微镜观察扩散的染色质时，活性rRNA基因具有特征性的圣诞树外观：从DNA“树干”延伸出紧密排列的新生转录物“分支”，其末端装饰有末端“球”。“这些终端球已经被发现了二十多年，在大多数生物教科书中都有介绍，并在数百篇论文中报道，但它们的性质仍然难以捉摸。在这里，我们表明，非洲爪蟾核糖体初级转录物的5 '-外部转录间隔区（ETS）中的rRNA加工信号与非洲爪蟾卵母细胞的因子形成了一个大的加工相关复合物，类似于在其他脊椎动物细胞类型中发现的5' ETS加工复合物。使用突变的rRNA基因，我们发现，同样的rRNA残基是必需的，这种生化定义的复杂的形成和终端球的形成，电子显微镜分析后，这些克隆的基因注入非洲爪蟾卵母细胞。这一点，加上其他提出的证据，意味着非洲爪蟾中的rRNA末端球，并通过推理，也在许多其他物种中观察到它们，是在新生rRNA上形成的进化上保守的5' ETS加工复合物的超微结构可视化。
When spread chromatin is visualized by electron microscopy, active rRNA genes have a characteristic Christmas tree appearance: From a DNA ''trunk'' extend closely packed ''branches'' of nascent transcripts whose ends are decorated with terminal ''balls.'' These terminal balls have been known for more than two decades, are shown in most biology textbooks, and are reported in hundreds of papers, yet their nature has remained elusive. Here, we show that a rRNA-processing signal in the 5'-external transcribed spacer (ETS) of the Xenopus laevis ribosomal primary transcript forms a large, processing-related complex with factors of the Xenopus oocyte, analogous to 5' ETS processing complexes found in other vertebrate cell types. Using mutant rRNA genes, we find that the same rRNA residues are required for this biochemically defined complex formation and for terminal ball formation, analyzed electron microscopically after injection of these cloned genes into Xenopus oocytes. This, plus other presented evidence, implies that rRNA terminal balls in Xenopus, and by inference, also in the multitude of other species where they have been observed, are the ultrastructural visualization of an evolutionarily conserved 5' ETS processing complex that forms on the nascent rRNA.