Nuclear pore complex architecture and functional dynamics.

Abstract

The vertebrate nuclear pore complex (NPC) is a ∼125-MDa supramolecular assembly, embedded in the double membrane of the nuclear envelope (NE). The NPC enables passive diffusion of ions and small molecules and mediated, signal-dependent, bidirectional nucleocytoplasmic transport of proteins, RNAs and RNP particles (reviewed in Izaurralde and Aupdam 1998; Ohno et al. 1998; Mattaj and Englmeier 1998; Adam 1999. Extensive electron microscopic (EM) analyses of isolated amphibian NEs have revealed a consensus model of the three-dimensional (3-D) architecture of the NPC (reviewed in PantÉ and Aebi 1996a Stoffler et al. 1999a. Accordingly, the NPC consists of a ∼55-MDa central framework (also termed “spoke complex”) that is sandwiched between a ∼32-MDa cytoplasmic ring and a ≈21-MDa nuclear ring (Fig. 1). The cytoplasmic ring is decorated by eight ∼50-nm-long kinky fibrils, whereas a “basket” (or “fishtrap”) tops the nuclear ring, which is assembled from eight ∼50–100-nm-long fibrils that join distally to form a 30–50-nm diameter distal ring. The ring-Hke central framework embraces a central pore or channel that mediates the signal-dependent transport of molecules in and out of the nucleus. Ions as well as small molecules diffuse passively between the cytoplasm and the nucleus, possibly through eight peripheral channels that perforate the central framework. Frequently, the central channel appears plugged by a “particle” of variable size and morphology whose definite structure and function remain to be established (see below).