The dynamics of karyopherin-mediated nuclear transport

The regulated exchange of proteins and nucleic acids between the nucleus an d cytoplasm demands a complex interplay between nuclear pore complexes (NPC s), which provide conduits in the nuclear envelope, and mobile transport re ceptors (or karyopherins, also known as importins/exportins) that bind and mediate the translocation of cargoes through the NPCs. Biochemical characte rization of individual karyopherins has led to the identification of many o f their cargoes and to the elucidation of the mechanisms by which they medi ate transport. Likewise, the characterization of numerous NPC-associated co mponents, in combination with structural studies of NPCs, have begun to add ress the possible mechanisms that drive nucleocytoplasmic transport, and th e role that different nucleoporins play in the transport process. Some rece nt studies indicate that several NPC-associated factors, previously thought to be stable components of the NPC, dynamically interact with both nuclear and cytoplasmic aspects of the NPC. The mobility of these components chall enges our conventional view of the NPC as the stationary phase of transport . These components and their potiential roles in nucleo-cytoplasmic transpo rt are discussed.