Panté N, Jarmolowski A, Izaurralde E, Sauder U, Baschong W, Mattaj I W
M.E. Müller Institute for Microscopy, Biozentrum, University of Basel,Switzerland.
RNA. 1997 May;3(5):498-513.
Export of RNA from the cell nucleus to the cytoplasm occurs through nuclear pore complexes (NPCs). To examine nuclear export of RNA, we have gold-labeled different types of RNA (i.e., mRNA, tRNA, U snRNAs), and followed their export by electron microscopy (EM) after their microinjection into Xenopus oocyte nuclei. By changing the polarity of the negatively charged colloidal gold, complexes with mRNA, tRNA, and U1 snRNA can be formed efficiently, and gold-tagged RNAs are exported to the cytoplasm with kinetics and specific saturation behavior similar to that of unlabeled RNAs. U6 snRNA conjugates, in contrast, remain in the nucleus, as does naked U6 snRNA. During export, RNA-gold was found distributed along the central axis of the NPC, within the nuclear basket, or accumulated at the nuclear and cytoplasmic periphery of the central gated channel, but not associated with the cytoplasmic fibrils. In an attempt to identify the initial NPC docking site(s) for RNA, we have explored various conditions that either yield docking of import ligands to the NPC or inhibit the export of nuclear RNAs. Surprisingly, we failed to observe docking of RNA destined for export at the nuclear periphery of the NPC under any of these conditions. Instead, each condition in which export of any of the RNA-gold conjugates was inhibited caused accumulation of gold particles scattered uniformly throughout the nucleoplasm. These results point to the existence of steps in export involving mobilization of the export substrate from the nucleoplasm to the NPC.
RNA从细胞核输出到细胞质是通过核孔复合体（NPCs）进行的。为了研究RNA的核输出，我们用金标记了不同类型的RNA（即mRNA、tRNA、U snRNAs），并在将它们显微注射到非洲爪蟾卵母细胞核后，通过电子显微镜（EM）追踪其输出情况。通过改变带负电荷的胶体金的极性，可以有效地形成与mRNA、tRNA和U1 snRNA的复合物，并且金标记的RNA以与未标记RNA相似的动力学和特定饱和行为输出到细胞质中。相比之下，U6 snRNA缀合物以及裸露的U6 snRNA都留在细胞核中。在输出过程中，发现RNA-金沿着NPC的中轴线分布，在核篮内，或聚集在中央门控通道的核周和胞质周边，但不与胞质纤丝相关。为了确定RNA最初的NPC对接位点，我们探索了各种条件，这些条件要么使输入配体与NPC对接，要么抑制核RNA的输出。令人惊讶的是，在任何这些条件下，我们都未能观察到注定要输出的RNA在NPC的核周边对接。相反，任何一种RNA-金缀合物的输出受到抑制的条件都会导致金颗粒均匀地散布在整个核质中积累。这些结果表明，在输出过程中存在一些步骤，涉及将输出底物从核质转移到NPC。
