Görlich D, Vogel F, Mills A D, Hartmann E, Laskey R A
Wellcome/CRC Institute, Cambridge, UK.
Nature. 1995 Sep 21;377(6546):246-8. doi: 10.1038/377246a0.
The import of nuclear proteins proceeds through the nuclear pore complex and requires nuclear localization signals (NLSs), energy and soluble factors, namely importin-alpha (M(r) 60K), importin-beta (90K) and Ran. Importin-alpha is primarily responsible for NLS recognition and is a member of a protein family that includes the essential yeast nuclear pore protein SRP1p (ref. 16). As the first event, the complex of importin-alpha and importin-beta binds the import substrate in the cytosol. Here we show that this nuclear pore targeting complex initially docks as a single entity to the nuclear pore via importin-beta. Then the energy-dependent, Ran-mediated translocation through the pore results in the accumulation of import substrate and importin-alpha in the nucleus. In contrast, importin-beta accumulates at the nuclear envelope, but not in the nucleoplasm. Immunoelectron microscopy detects importin-beta on both sides of the nuclear pore. This suggests that the nuclear pore targeting complex might move as a single entity from its initial docking site through the central part of the nuclear pore before it disassembles on the nucleoplasmic side.
核蛋白的输入通过核孔复合体进行，需要核定位信号（NLSs）、能量和可溶性因子，即输入蛋白α（分子量60K）、输入蛋白β（90K）和Ran。输入蛋白α主要负责NLS的识别，是一个蛋白质家族的成员，该家族包括酵母必需的核孔蛋白SRP1p（参考文献16）。作为第一步，输入蛋白α和输入蛋白β的复合体在细胞质中结合输入底物。我们在此表明，这种核孔靶向复合体最初作为一个单一实体通过输入蛋白β停靠在核孔上。然后，依赖能量的、Ran介导的通过核孔的转运导致输入底物和输入蛋白α在细胞核中积累。相比之下，输入蛋白β在核膜处积累，但不在核质中积累。免疫电子显微镜在核孔两侧都检测到了输入蛋白β。这表明核孔靶向复合体可能作为一个单一实体从其初始停靠位点穿过核孔的中心部分，然后在核质侧解体之前移动。
