Protein Transport Between the Nucleus and Cytoplasm

Abstract Bidirectional macromolecular traffic between the nucleus and cytoplasm, which occurs through nuclear pore complexes (NPCs), is mediated by specific subsets of proteins. Nuclear transport factors recognize a short stretch of signals on cargo molecules and carry the cargo into and/or out of the nucleus. The nucleocytoplasmic gradient of Ran, a small G protein, is essential for directed nuclear transport. Both the overall structures of the key components and basic mechanisms of nuclear transport are well conserved from budding yeast to humans. However, the nuclear transport system has diverged during evolution to become finely tuned, which is essential for various physiological processes, particularly in higher eukaryotes. In addition, increasing evidence has revealed that nuclear transport-related factors play roles in nontransport-related cellular processes. This chapter introduces the basic molecular mechanism of nucleocytoplasmic protein transport through NPCs and discusses their physiological significance in various cellular functions.