Zhao Jian, Jin Shao-Bo, Wieslander Lars
Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden.
J Cell Sci. 2004 Mar 15;117(Pt 8):1553-66. doi: 10.1242/jcs.00992.
Messenger RNA is formed from precursors known as pre-mRNA. These precursors associate with proteins to form pre-mRNA-protein (pre-mRNP) complexes. Processing machines cap, splice and polyadenylate the pre-mRNP and in this way build the mRNP. These processing machines also affect the export of the mRNP complexes from the nucleus to the cytoplasm. Export to the cytoplasm takes place through a structure in the nuclear membrane called the nuclear pore complex (NPC). Export involves adapter proteins in the mRNP and receptor proteins that bind to the adapter proteins and to components of the NPC. We show that the export receptor chromosomal region maintenance protein 1 (CRM1), belonging to a family of proteins known as importin-beta-like proteins, binds to gene-specific Balbiani ring (BR) pre-mRNP while transcription takes place. We also show that the GTPase known as Ran binds to BR pre-mRNP, and that it binds mainly in the interchromatin. However, we also show using leptomycin B treatment that a NES-CRM1-RanGTP complex is not essential for export, even though both CRM1 and Ran accompany the BR mRNP through the NPC. Our results therefore suggest that several export receptors associate with BR mRNP and that these receptors have redundant functions in the nuclear export of BR mRNP.
信使核糖核酸（mRNA）由称为前体mRNA的前体形成。这些前体与蛋白质结合形成前体mRNA-蛋白质（pre-mRNP）复合物。加工机器对前体mRNA进行加帽、剪接和聚腺苷酸化，从而构建出mRNP。这些加工机器还会影响mRNP复合物从细胞核输出到细胞质的过程。向细胞质的输出通过核膜上一种称为核孔复合体（NPC）的结构进行。输出过程涉及mRNP中的衔接蛋白以及与衔接蛋白和NPC成分结合的受体蛋白。我们发现，属于一类称为输入蛋白β样蛋白家族的输出受体染色体区域维持蛋白1（CRM1），在转录发生时与基因特异性的巴尔比亚尼环（BR）前体mRNA结合。我们还发现，称为Ran的GTP酶与BR前体mRNA结合，并且主要在染色质间结合。然而，我们通过雷帕霉素B处理也表明，即使CRM1和Ran都伴随BR mRNP通过NPC，但NES-CRM1-RanGTP复合物对于输出并非必不可少。因此，我们的结果表明，几种输出受体与BR mRNP相关联，并且这些受体在BR mRNP的核输出中具有冗余功能。
