Moroianu J
Laboratory of Cell Biology, Rockefeller University, New York, NY 10021, USA.
Crit Rev Eukaryot Gene Expr. 1997;7(1-2):61-72. doi: 10.1615/critreveukargeneexpr.v7.i1-2.40.
Transport of proteins into and out of the nucleus occurs through nuclear pore complexes (NPC). A heterodimeric protein complex, composed of karyopherin alpha and beta (or importin alpha and beta) functions to target proteins containing a nuclear localization sequence (NLS) to the NPCs. Two additional proteins, the GTPase Ran and p10, are required to translocate the docked NLS protein into the nucleus. The alpha subunit of karyopherin functions as the NLS receptor, whereas the beta subunit mediates docking to nucleoporins that contain peptide repeats. During import the karyopherin heterodimer dissociates: karyopherin alpha and import substrates enter and accumulate in the nucleoplasm, whereas karyopherin beta accumulates at the nuclear pore complex. Ran-GTP induces dissociation of karyopherin alpha from beta by forming a complex with karyopherin beta and promotes the release of both karyopherin subunits from a docking site. Protein transport across the NPC may occur via guided diffusion involving the karyopherin-mediated docking and undocking of import substrate to multiple binding sites that extend from the cytoplasmic to the nucleoplasmic ends of the NPC.
蛋白质进出细胞核是通过核孔复合体（NPC）进行的。一种由核转运蛋白α和β（或输入蛋白α和β）组成的异二聚体蛋白复合体，其功能是将含有核定位序列（NLS）的蛋白质靶向到核孔复合体。还需要另外两种蛋白质，即GTP酶Ran和p10，才能将停靠的NLS蛋白转运到细胞核中。核转运蛋白的α亚基作为NLS受体，而β亚基介导与含有肽重复序列的核孔蛋白对接。在输入过程中，核转运蛋白异二聚体解离：核转运蛋白α和输入底物进入并积聚在核质中，而核转运蛋白β积聚在核孔复合体处。Ran-GTP通过与核转运蛋白β形成复合体诱导核转运蛋白α与β解离，并促进两个核转运蛋白亚基从对接位点释放。蛋白质穿过核孔复合体可能通过引导扩散发生，这涉及核转运蛋白介导的输入底物与从核孔复合体的细胞质端延伸到核质端的多个结合位点的对接和脱离对接。
