Pore relations: nuclear pore complexes and nucleocytoplasmic exchange.

NPCs are the sole sites of exchange between the nucleus and cytoplasm. A large family of transport factors carry cargo between the nucleus and cytoplasm through the NPC. The NPC is a huge symmetric octagonal structure comprised of dozens of NUPs. NUPs make many contacts with surrounding structures, including the NE, the cytoplasm and nuclear interior. A subset of NUPs contain repeated peptide motifs that serve as docking sites for transport factors. The directionality of transport is determined by the transport factor, and its interactions with the small GTPase Ran and NUPs. Very little is known about how the NPC mediates transport, NPC assembly and the NPC's role in regulating transport, but these areas of research are beginning to emerge.