Protein import into the nucleus.

The transport of proteins from the cytoplasm into the nucleus is a multistep process. The nuclear localization sequence (NLS) of a transport substrate associates with the heterodimeric NLS-receptor which binds to a subset of proteins of the nuclear pore complex (NPC). Translocation through the NPC is energy-dependent and requires the small GTPase Ran. Proteins that interact with Ran in either the GDP-bound or the GTP-bound state coordinate transfer through the NPC. Lastly, the NLS-receptor/ substrate complex and Ran reach the nuclear side of the NPC where the complex disassembles.