NUCLEAR-PORE COMPLEX - STRUCTURE, FUNCTION, AND REGULATION

From the large amount of data summarized in this review, it is clear that our knowledge of the NPC and nuclear transport is increasing rapidly. It is also becoming clear how important nuclear transport is to the physiology of the cell. A few simplifying assumptions have already emerged; the control of movement of RNA and nuclear proteins across the nuclear membrane share some common features. It has become clear that for both RNA and nuclear proteins, anchoring of these macromolecules may play a role in preventing transport. Dissociation from the anchor may be important for the signaling process. Shuttles may also play key roles in transport. These shuttling molecules may move between the nuclear and cytoplasmic compartments, directing the proper compartmentalization of macromolecules bound to them. It is also clear that transport of both RNA and nuclear proteins requires the participation of the nucleoporins, a family of nuclear pore glycoproteins modified by O-linked GlcNAc. The recent cloning and identification of several of these molecules may facilitate studies attempting to address the mechanism of the transport machinery. Of course, understanding the molecular details of the NPC itself, a structure 125 MDa in molecular mass, will be a long and difficult task. However, the combination of approaches being applied to this problem may ultimately identify the critical components of the nuclear pore and the nuclear transport machinery that characterizes all eucaryotic cells.