Takeiwa Toshihiko, Taniguchi Ichiro, Ohno Mutsuhito
Institute for Virus Research, Kyoto University, Kyoto, 606-8507, Japan.
Genes Cells. 2015 Apr;20(4):281-91. doi: 10.1111/gtc.12218. Epub 2015 Feb 4.
The signal recognition particle is a ribonucleoprotein complex that is essential for the translocation of nascent proteins into the endoplasmic reticulum. It has been shown that the RNA component (SRP RNA) is exported from the nucleus by CRM1 in the budding yeast. However, how SRP RNA is exported in higher species has been elusive. Here, we show that SRP RNA does not use the CRM1 pathway in Xenopus oocytes. Instead, SRP RNA uses the same export pathway as pre-miRNA and tRNA as showed by cross-competition experiments. Consistently, the recombinant Exportin-5 protein specifically stimulated export of SRP RNA as well as of pre-miRNA and tRNA, whereas an antibody raised against Exportin-5 specifically inhibited export of the same RNA species. Moreover, biotinylated SRP RNA can pull down Exportin-5 but not CRM1 from HeLa cell nuclear extracts in a RanGTP-dependent manner. These results, taken together, strongly suggest that the principal export receptor for SRP RNA in vertebrates is Exportin-5 unlike in the budding yeast.
信号识别颗粒是一种核糖核蛋白复合体，对于新生蛋白质转运到内质网至关重要。研究表明，在出芽酵母中，RNA组分（SRP RNA）通过CRM1从细胞核输出。然而，SRP RNA在高等生物中如何输出一直不清楚。在此，我们表明在非洲爪蟾卵母细胞中，SRP RNA不使用CRM1途径。相反，交叉竞争实验表明，SRP RNA与前体miRNA和tRNA使用相同的输出途径。一致地，重组的Exportin-5蛋白特异性地刺激SRP RNA以及前体miRNA和tRNA的输出，而针对Exportin-5产生的抗体特异性地抑制相同RNA种类的输出。此外，生物素化的SRP RNA能够以RanGTP依赖的方式从HeLa细胞核提取物中拉下Exportin-5，但不能拉下CRM1。综上所述，这些结果强烈表明，与出芽酵母不同，脊椎动物中SRP RNA的主要输出受体是Exportin-5。
