13 - Nucleocytoplasmic Transport

Abstract

This chapter outlines the nucleocytoplasmic transport. The cell nucleus is the most prominent cellular organelle and the defining feature of the eukaryotic branch of life. The transport machinery employs roughly 100 different, often highly abundant proteins and thus utilizes considerable cellular resources. Facilitated transport through NPCs does not occur at random, but instead in a signal- and receptor-mediated fashion. This chapter depicts a Cut-open Model of an NPC embedded in a nuclear envelop along with transport cycles of importins (Imp) and exportins (Exp) and their coordination by the RanGTPase system. Many of the fundamental insights into the nuclear transport machinery were gained through studying the import of proteins that carry a so-called classical nuclear localization signal (NLS). Interestingly, the Imp/dimer not only functions during interphase in nuclear import, but also has a function in mitosis, where it helps to orient the mitotic spindle. The chapter highlights that the biogenesis of ribosomes is a very complex process which involves both nuclear import and export events. The translocating species could thus selectively partition into the permeability barrier and use this “selective solvation” to cross this permeability barrier at a high rate. In other words, the plug would seal around the translocating species and remain a barrier for inert molecules even when large objects pass. Finally, this chapter also summarizes nuclear pore complexes and its functions.