Function and molecular properties of nuclear pore-targeting complex

蛋白质的核输入是由细胞质中核定位信号（NLS）依赖性复合物（称为核孔靶向复合物（PTAC））的形成启动的。PTAC是一种稳定的蛋白质复合物，由亲核蛋白和两种称为PTAC 58/importin α和PTAC 97/importin β的胞质组分组成。Importin α直接与嗜核细胞的NLS结合，Importin β为PTAC提供核孔复合物（NPC）结合位点。我们分析了importin α和importin β的性质，得到如下结果：1.我们已经鉴定了另外三个与已知importin α同源的小鼠基因，并表明小鼠importin α可以分为三个亚家族（Rch 1，NPI 1和Qip 1），彼此之间显示出约50%的氨基酸同一性。2.结果表明，importin α家族蛋白对底物的识别具有一定的特异性。例如，Qip 1识别非常有限的NLS，需要上游序列和基本核心序列 关于我们 Q1 ATP酶的底物识别。另一个证据是酪氨酸磷酸化的Stat被NPI 1识别，而不是Rch 1。Stat 1不具有典型的碱性NLS，与NPI 1的结合部位与SV 40 T抗原碱性NLS结合部位不同。3.我们研究了importin β的行为和功能结构域Importin β通过NPC在细胞质和细胞核之间快速穿梭。缺失突变体的使用揭示了输入蛋白β的NPC-易位既不需要Ran-也不需要输入蛋白α-结合，而仅需要该分子的NPC-结合结构域。发现NPC转运importin β既不需要Ran也不需要其GTP水解。此外，importin β具有自身转运NPC的能力。这可能是运输因子的一个共同特征，它们通过NPC将某些货物运送到细胞核内外。4.我们检查了β-连环蛋白的核输入，发现β-连环蛋白可以自行转运NPC，而不需要包括Ran在内的可溶性因子。Β-catenin可能与importin β具有相同的NPC易位特性。少

Nuclear import of proteins arc initiated by nuclear localization signal (NLS)-dependent complex formation, termed the nuclear pore-targeting complex (PTAC), in the cytoplasm. PTAC is a stable protein complex composed of a karyophilic protein and two cytosolic components termed PTAC58/importin α and PTAC97/importin β. Importin α directly binds to NLS of karyophile and importin β provides nuclear pore complex (NPC) binding site for PTAC. We analyzed the properties of importin α and importin β, and obtained the following results : 1. We have identified three additional mouse genes homologous to the known importin α, and showed that the mouse importin α can be classified into three subfamilies (Rch1, NPI1, and Qip1), showing approximately 50% amino acid identity to one another. 2. We showed that importin α family proteins show some specificities in the recognition of substrates. For example, Qip1 recognizes a very restricted NLS, requiring both the upstream sequence and basic core sequence … More of Q1 ATPase for its substrate recognition. The other evidence is that tyrosine phosphorylated Stat his recognized by NPI1, but not Rch1. Stat 1 apparently does not possess typical basic-type NLS, and it binds to different portion of NPI1 from those of SV40 T-antigen basic NLS binding site. 3. We examined the behavior and functional domain of importin β Importin β rapidly shuttles between the cytoplasm and the nucleus through NPCs. The use of deletion mutants reveals that NPC-translocation of importin β requires neither Ran- nor importin α-binding but only the NPC-binding domain of this molecule. NPC translocation of importin β was found to require neither Ran nor its GTP hydrolysis. Furthermore, importin β possesses ability to translocate NPC on its own. This could be a common feature of transport factors that carries certain cargos through NPCs into and out of the nucleus. 4. We examined the nuclear import of β-catenin and found that b-catenin can translocate NPCs on it own without requiring soluble factors including Ran. Β-catenin is likely to share the same property with importin β for NPC translocation. Less