The Part and the Whole: functions of nucleoporins in nucleocytoplasmic transport

The nuclear pore complex (NPC) functions as a selective gate that allows passage of certain molecules into and out of the nucleus and restricts that of others. Nucleoporins, the protein components of the NPC, can have a predominantly structural function but also take active roles in nuclear transport. First, multiple nucleoporins with phenylalanine-glycine (FG) repeats appear to act as an entity, forming a barrier that is permeable for only a subset of macromolecules. Second, individual nucleoporins can specifically affect individual transport pathways. To contrast and compare these different functions of nucleoporins, we review the models that try to explain selective transport on the basis of FG-nucleoporins and discuss the role of individual nucleoporins in nuclear import and export.