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首页> 外文期刊>Molecular and Cellular Biology >Human Nopp140, Which Interacts with RNA Polymerase I: Implications for rRNA Gene Transcription and Nucleolar Structural Organization
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Human Nopp140, Which Interacts with RNA Polymerase I: Implications for rRNA Gene Transcription and Nucleolar Structural Organization

机译：人Nopp140，与RNA聚合酶I相互作用：对rRNA基因转录和核仁结构组织的影响。

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Nopp140 is thought to shuttle between nucleolus and cytoplasm. However, the predominant nucleolar localization of Nopp140 homologues from different species suggests that Nopp140 is also involved in events occurring within the nucleolus. In this study, we demonstrated that the largest subunit of RNA polymerase I, RPA194, was coimmunoprecipitated with the human Nopp140 (hNopp140). Such an interaction is mediated through amino acids 204 to 382 of hNopp140. By double immunofluorescence, hNopp140 was colocalized with RNA polymerase I at the rDNA (rRNA genes) transcription active foci in the nucleolus. These results suggest that Nopp140 can interact with RNA polymerase I in vivo. Transfected cells expressing the amino-terminal half of hNopp140, hNopp140N382 (amino acids 1 to 382), displayed altered nucleoli with crescent-shaped structures. This phenotype is reminiscent of the segregated nucleoli induced by actinomycin D treatment, which is known to inhibit rRNA synthesis. Consistently, the hNopp140N382 protein mislocalized the endogenous RNA polymerase I and shut off cellular rRNA gene transcription as revealed by an in situ run-on assay. These dominant negative effects of the mutant hNopp140N382 suggest that Nopp140 plays an essential role in rDNA transcription. Interestingly, ectopic expression of hNopp140 to a very high level caused the formation of a transcriptionally inactive spherical structure occupying the entire nucleolar area which trapped the RNA polymerase I, fibrillarin, and hNopp140 but excluded the nucleolin. The mislocalizations of these nucleolar proteins after hNopp140 overexpression imply that Nopp140 may also play roles in maintenance of nucleolar integrity.
机译：Nopp140被认为在核仁和细胞质之间穿梭。然而，来自不同物种的Nopp140同源物的主要核仁定位表明Nopp140也参与核仁内发生的事件。在这项研究中，我们证明了RNA聚合酶I的最大亚基RPA194与人Nopp140（hNopp140）共免疫沉淀。这种相互作用是通过hNopp140的204至382位氨基酸介导的。通过双重免疫荧光，hNopp140与RNA聚合酶I共定位在核仁中的rDNA（rRNA基因）转录活性位点。这些结果表明，Nopp140可以在体内与RNA聚合酶I相互作用。表达hNopp140的氨基末端一半的转染细胞hNopp140N382（氨基酸1至382）显示出具有新月形结构的核仁。该表型使人联想起由放线菌素D处理诱导的分离的核仁，该处理已知抑制rRNA的合成。一致地，hNopp140N382蛋白错位了内源性RNA聚合酶I，并关闭了原位运行检测显示的细胞rRNA基因转录。突变体hNopp140N382的这些主要负作用表明，Nopp140在rDNA转录中起重要作用。有趣的是，hNopp140的异位表达水平很高，导致形成了一个转录失活的球形结构，占据了整个核仁区域，该区域捕获了RNA聚合酶I，纤维蛋白和hNopp140，但排除了核仁蛋白。 hNopp140过表达后，这些核仁蛋白的错误定位暗示Nopp140可能在维持核仁完整性中也起着作用。

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