Izaurralde E, Jarmolowski A, Beisel C, Mattaj I W, Dreyfuss G, Fischer U
European Molecular Biology Laboratory, Heidelberg, Germany.
J Cell Biol. 1997 Apr 7;137(1):27-35. doi: 10.1083/jcb.137.1.27.
Among the nuclear proteins associated with mRNAs before their export to the cytoplasm are the abundant heterogeneous nuclear (hn) RNPs. Several of these contain the M9 signal that, in the case of hnRNP A1, has been shown to be sufficient to signal both nuclear export and nuclear import in cultured somatic cells. Kinetic competition experiments are used here to demonstrate that M9-directed nuclear import in Xenopus oocytes is a saturable process. Saturating levels of M9 have, however, no effect on the import of either U snRNPs or proteins carrying a classical basic NLS. Previous work demonstrated the existence of nuclear export factors specific for particular classes of RNA. Injection of hnRNP A1 but not of a mutant protein lacking the M9 domain inhibited export of mRNA but not of other classes of RNA. This suggests that hnRNP A1 or other proteins containing an M9 domain play a role in mRNA export from the nucleus. However, the requirement for M9 function in mRNA export is not identical to that in hnRNP A1 protein transport.
在mRNA输出到细胞质之前与之相关的核蛋白中，丰富的不均一核（hn）核糖核蛋白是其中之一。其中几种含有M9信号，就hnRNP A1而言，已证明该信号足以在培养的体细胞中发出核输出和核输入的信号。本文使用动力学竞争实验来证明非洲爪蟾卵母细胞中M9介导的核输入是一个可饱和的过程。然而，饱和水平的M9对U小核核糖核蛋白或携带经典碱性核定位信号的蛋白质的输入没有影响。先前的研究表明存在特定类别的RNA特有的核输出因子。注射hnRNP A1而不是缺乏M9结构域的突变蛋白会抑制mRNA的输出，但不会抑制其他类别的RNA的输出。这表明hnRNP A1或其他含有M9结构域的蛋白质在mRNA从细胞核输出中起作用。然而，mRNA输出中对M9功能的需求与hnRNP A1蛋白运输中的需求并不相同。
