The vertebrate nuclear pore complex: from structure to function.

Abstract

In interphase eukaryotic cells, the cytoplasm is spatially separated from the cell nucleus by the double-membraned nuclear envelope (NE). Inserted into the NE are nuclear pore complexes (NPCs) which mediate bidirectional nucleocytoplasmic transport, i.e. the passive diffusion of ions and small molecules as well as the signal-mediated transport of proteins, RNAs and RNP particles in and out of the nucleus (reviewed in Izaurralde and Adam 1998; Mattaj and Englmeier 1998; Ohno et al. 1998; Gorlich and Kutay 1999). Extensive electron microscopy studies, predominantly on Xenopus oocytes, have revealed the three-dimensional (3-D) architecture of the NPC (reviewed in Pante and Aebi 1996a; Stoffler et al. 1999a; Allen et al. 2000; Fahrenkrog et al. 2001). Accordingly, the vertebrate NPC reveals an eight-fold symmetric (i.e. in the plane of the NE) tripartite (i.e. perpendicular to the plane of the NE) architecture with a total mass of ~125 MDa. The ~55 MDa central framework of the NPC (also called the spoke complex) is built of eight multi-domain spokes, each consisting of two roughly identical halves (Fig. 1). The central framework is sandwiched between a ~32 MDa cytoplasmic and a ~21 MDa nuclear ring moiety. Eight short kinky fibrils emanate from the cytoplasmic ring, protruding into the cytoplasm, whereas the nuclear ring is capped by a basket-like assembly (also called the fish-trap), made of eight thin fibrils that join distally so as to form an iris-like ring.