Pemberton L F, Rosenblum J S, Blobel G
Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York 10021, USA.
J Cell Biol. 1997 Dec 29;139(7):1645-53. doi: 10.1083/jcb.139.7.1645.
Three independent pathways of nuclear import have so far been identified in yeast, each mediated by cognate nuclear transport factors, or karyopherins. Here we have characterized a new pathway to the nucleus, mediated by Mtr10p, a protein first identified in a screen for strains defective in polyadenylated RNA export. Mtr10p is shown to be responsible for the nuclear import of the shuttling mRNA-binding protein Npl3p. A complex of Mtr10p and Npl3p was detected in cytosol, and deletion of Mtr10p was shown to lead to the mislocalization of nuclear Npl3p to the cytoplasm, correlating with a block in import. Mtr10p bound peptide repeat-containing nucleoporins and Ran, suggesting that this import pathway involves a docking step at the nuclear pore complex and is Ran dependent. This pathway of Npl3p import is distinct and does not appear to overlap with another known import pathway for an mRNA-binding protein. Thus, at least two parallel pathways function in the import of mRNA-binding proteins, suggesting the need for the coordination of these pathways.
到目前为止，在酵母中已鉴定出三种独立的核输入途径，每种途径都由同源核转运因子或核转运蛋白介导。在这里，我们描述了一种新的细胞核途径，该途径由Mtr10p介导，Mtr10p是一种首先在聚腺苷酸化RNA输出缺陷菌株筛选中发现的蛋白质。研究表明，Mtr10p负责穿梭mRNA结合蛋白Npl3p的核输入。在细胞质中检测到Mtr10p和Npl3p的复合物，并且Mtr10p的缺失导致核Npl3p错误定位于细胞质，这与输入受阻相关。Mtr10p结合含肽重复序列的核孔蛋白和Ran，表明该输入途径涉及在核孔复合体处的对接步骤并且是Ran依赖性的。Npl3p的这种输入途径是独特的，并且似乎与另一种已知的mRNA结合蛋白输入途径不重叠。因此，至少有两条平行途径在mRNA结合蛋白的输入中起作用，这表明需要协调这些途径。
