Mattaj I W, Englmeier L
European Molecular Biology Laboratory, Heidelberg, Germany.
Annu Rev Biochem. 1998;67:265-306. doi: 10.1146/annurev.biochem.67.1.265.
Active transport between the nucleus and cytoplasm involves primarily three classes of macromolecules: substrates, adaptors, and receptors. Some transport substrates bind directly to an import or an export receptor while others require one or more adaptors to mediate formation of a receptor-substrate complex. Once assembled, these transport complexes are transferred in one direction across the nuclear envelope through aqueous channels that are part of the nuclear pore complexes (NPCs). Dissociation of the transport complex must then take place, and both adaptors and receptors must be recycled through the NPC to allow another round of transport to occur. Directionality of either import or export therefore depends on association between a substrate and its receptor on one side of the nuclear envelope and dissociation on the other. The Ran GTPase is critical in generating this asymmetry. Regulation of nucleocytoplasmic transport generally involves specific inhibition of the formation of a transport complex; however, more global forms of regulation also occur.
转运底物、衔接蛋白和受体。一些运输底物直接与输入或输出受体结合，而其他底物则需要一个或多个衔接蛋白来介导受体 - 底物复合物的形成。一旦组装完成，这些运输复合物通过作为核孔复合体（NPC）一部分的水通道在一个方向上穿过核膜。然后运输复合物必须解离，衔接蛋白和受体都必须通过NPC循环利用，以允许进行另一轮运输。因此，输入或输出的方向性取决于核膜一侧底物与其受体之间的结合以及另一侧的解离。Ran GTP酶在产生这种不对称性方面至关重要。核质运输的调节通常涉及对运输复合物形成的特异性抑制；然而，也会出现更全面的调节形式。
