Structural and functional insights into nucleocytoplasmic transport.

The cell nucleus is surrounded by a double membrane system, the nuclear envelope (NE), with the outer nuclear membrane being continuous with the endoplasmic reticulum. Nuclear pore complexes (NPCs) fuse the inner and outer nuclear membranes, forming aqueous channels that allow free diffusion of small molecules but that also mediate the energy-dependent transport of large macromolecules. The NPC represents the largest known molecular complex and is composed of about 30 different proteins, termed nucleoporins (Nups). Here, we review recent studies that provide novel insight into the structural and functional organization of nucleocytoplasmic transport. In addition, prospects towards a high resolution model of the nuclear pore are discussed.