Nakielny S, Dreyfuss G
Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6148, USA.
Curr Biol. 1998 Jan 15;8(2):89-95. doi: 10.1016/s0960-9822(98)70039-9.
Nuclear protein import and export are mediated by receptor proteins that recognize nuclear localization sequences (NLSs) or nuclear export sequences (NESs) and target the NLS-bearing or NES-bearing protein to the nuclear pore complex (NPC). Temperature-dependent translocation of the receptor-cargo complex in both directions through the NPC requires the GTPase Ran, and it has been proposed that the Ran GTPase cycle mediates translocation. We have addressed the role of GTP hydrolysis in these processes by studying the import receptor transportin, which mediates the import of a group of abundant heterogeneous nuclear RNA-binding proteins bearing the M9 NLS.
We investigated the transport properties of transportin and found that the carboxy-terminal region of transportin could, by itself, be imported into the nucleus. Transportin import and export were inhibited by low temperature in vitro, but were unaffected by the non-hydrolyzable GTP analogue GMP-PNP.
Temperature-dependent import and export through the NPC can be uncoupled from the Ran GTPase cycle and can occur without GTP hydrolysis.
核蛋白的输入和输出由受体蛋白介导，这些受体蛋白识别核定位序列（NLSs）或核输出序列（NESs），并将携带NLS或NES的蛋白靶向至核孔复合体（NPC）。受体 - 货物复合体通过NPC在两个方向上的温度依赖性转运需要GTP酶Ran，并且有人提出Ran GTP酶循环介导转运。我们通过研究输入受体转运蛋白来探讨GTP水解在这些过程中的作用，转运蛋白介导一组携带M9 NLS的丰富异质核RNA结合蛋白的输入。
我们研究了转运蛋白的转运特性，发现转运蛋白的羧基末端区域自身可被输入细胞核。在体外，转运蛋白的输入和输出受低温抑制，但不受不可水解的GTP类似物GMP - PNP的影响。
通过NPC的温度依赖性输入和输出可以与Ran GTP酶循环解偶联，并且可以在没有GTP水解的情况下发生。
