Importins/Karyopherins Meet Nucleoporins

with the goal of identifying the numerous nuclear pore Universitä t Heidelberg proteins and studying their role in nucleocytoplasmic Institut fü r Biochemie I transport. Recently, the purification of milligram quanti-Im Neuenheimer Feld 328 ties of highly enriched yeast NPCs and a genetic dissec-D-69120 Heidelberg tion of the NPC gave a burst of knowledge on the nature Federal Republic of Germany of nuclear pore proteins and factors involved in nucleo-cytoplasmic transport (reviewed by Rout and Wente, The Architecture and Biogenesis of the NPC this research field is currently providing novel insights Electron microscopy (EM) analysis of the NPC over the into the mechanism of nucleocytoplasmic transport and past 25 years has provided a detailed structural picture the organization of the nuclear pore complex (NPC). of this 125 MDa macromolecular assembly. The NPC Besides research dealing with nuclear pore structure consists of four basic elements: the spoke–ring com-and function, other aspects concerning the functional plex, the central plug (" transporter "), cytoplasmic fibrils, organization of the cell nucleus into subcompartments and the inner nuclear basket. C. Akey (Boston University, and certain aspects of ribosome biogenesis were dis-Boston, Massachusetts) reported on a three-dimen-cussed at this meeting, which had the following topics: sional (3D) EM analysis of frozen/hydrated yeast NPCs molecular anatomy of the nuclear periphery, nucleocy-in ice. Accordingly, yeast NPCs are physically smaller toplasmic protein transport and its impact on transcrip-(about half the size in height and significantly smaller in tion and differentiation, nucleocytoplasmic transport of diameter) than higher eukaryotic NPCs, suggesting that ribonucleoproteins, functional topology of the cell nu-some structures are absent. In particular, yeast NPCs cleus, nuclear compartmentation, and ribosome biosyn-seem to lack a luminal spoke domain, which in verte-thesis. In this meeting review, I will focus mainly on brate NPCs has been attributed to the luminal domain presentations dealing with the NPC and nucleocytoplas-of gp210 (Jarnik and Aebi, 1991), raising the question mic transport and only summarize the essence of the of whether yeast lack a homolog to murine gp210. In other topics. contrast, the inner spoke ring and the central transporter In his historical overview on nucleocytoplasmic trans-of yeast NPCs highly resemble the corresponding struc-port, R. Laskey (Wellcome/Cancer Research Center In-tures in metazoans. Thus, different substructures of the stitute, Cambridge, United Kingdom) emphasized that NPC may have evolved independently. The ability to several phases of research were crucial for the develop-perform 3D reconstructions of NPCs will make it …