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Nuclear pore complexes (NPCs) are large protein assemblies embedded in the nuclear envelope that act as passageways for transport of molecules into and out of the nucleus. Two new studies, one in Nature Cell Biology and one in Science , offer direct evidence that the NPC is a highly dynamic structure.  相似文献   

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A new study shows that the filamentous fungus, Aspergillus nidulans, which has a closed mitosis, does not maintain a continuous permeability barrier during mitosis. This work challenges current views of the differences between closed and open mitosis and has implications for understanding mitotic specific changes in the nuclear pore complex and Ran GTPase system in lower eukaryotes.  相似文献   

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It is generally accepted that transport through the nuclear pore complex (NPC) involves an abundance of phenylalanine-glycine rich protein domains (FG-domains) that serve as docking sites for soluble nuclear transport receptors (NTRs) and their cargo complexes. But the precise mechanism of translocation through the NPC allowing for high speed and selectivity is still vividly debated. To ultimately decipher the underlying gating mechanism it is indispensable to shed more light on the molecular arrangement of FG-domains and the distribution of NTR-binding sites within the central channel of the NPC. In this review we revisit current transport models, summarize recent results regarding translocation through the NPC obtained by super-resolution microscopy and finally discuss the status and potential of optical methods in the analysis of the NPC.  相似文献   

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Caspases were recently implicated in the functional impairment of the nuclear pore complex during apoptosis, affecting its dual activity as nucleocytoplasmic transport channel and permeability barrier. Concurrently, electron microscopic data indicated that nuclear pore morphology is not overtly altered in apoptotic cells, raising the question of how caspases may deactivate nuclear pore function while leaving its overall structure largely intact. To clarify this issue we have analyzed the fate of all known nuclear pore proteins during apoptotic cell death. Our results show that only two of more than 20 nuclear pore core structure components, namely Nup93 and Nup96, are caspase targets. Both proteins are cleaved near their N terminus, disrupting the domains required for interaction with other nucleoporins actively involved in transport and providing the permeability barrier but dispensable for maintaining the nuclear pore scaffold. Caspase-mediated proteolysis of only few nuclear pore complex components may exemplify a general strategy of apoptotic cells to efficiently disable huge macromolecular machines.  相似文献   

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A nuclear pore complex (NPC) is a large protein assembly that mediates the nucleocytoplasmic exchange of molecules. During the cell cycle, NPCs assemble, disassemble, and dynamically change their distribution on assembled nuclear envelope (NE), whereas in post-mitosis, NPCs are extremely stable. Extensive studies on its components, structure, and building blocks allow the study of its assembly and disassembly at the molecular level. Depending on the location that the initial components of this structure are built (e.g. chromatin versus double lipid bilayers of the nuclear envelope), the regulation and the mechanism of the assembly differ. Moreover, cell cycle dynamics of NPC are linked with INM proteins, lamins, lipid membranes, and the cell cycle signal, which show that NPC dynamics are highly regulated processes.  相似文献   

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Nucleocytoplasmic trafficking of macromolecules, a highly specific and tightly regulated process, occurs exclusively through the nuclear pore complex. This immense structure is assembled from approximately 30 proteins, termed nucleoporins. Here we discuss the four nucleoporins that have been linked to cancers, either through elevated expression in tumors (Nup88) or through involvement in chromosomal translocations that encode chimeric fusion proteins (Tpr, Nup98, Nup214). In each case we consider the normal function of the nucleoporin and its translocation partners, as well as what is known about their mechanistic contributions to carcinogenesis, particularly in leukemias. Studies of nucleoporin-linked cancers have revealed novel mechanisms of oncogenesis and in the future, should continue to expand our understanding of cancer biology.  相似文献   

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Nuclear protein import: specificity for transport across the nuclear pore   总被引:13,自引:0,他引:13  
Transport of proteins into the cell nucleus is thought to require specific localization sequences and may be mediated by nuclear pores. Following microinjection into fused cultured cells, nuclear protein import was directly monitored by fluorescence microscopy using B-phycoerythrin (PE; Mr 240,000) coupled to synthetic peptides corresponding to the simian virus 40 (SV-40) large T antigen nuclear localization signal. Peptides with a single amino acid replacement found in a cytoplasmic mutant of T antigen (cT) failed to promote uptake. Further studies with deletion peptides revealed the minimum sequence requirements for efficient nuclear import of PE conjugates to be similar to those previously defined genetically for large T antigen itself. No competitive inhibition of uptake was observed in cells expressing nuclear or cytoplasmic T antigen. Nuclear import was time- and temperature-dependent. The lectin wheat germ agglutinin (WGA) binds to glycoproteins bearing O-linked GlcNAc on the cytoplasmic face of the nuclear pore in vitro [J.A. Hanover et al. (1987) J. Biol. Chem. 262, 9887-9894] and in vivo. Microinjection of WGA into the cytoplasm of living cells did not alter the diffusion of dextran (Mr 10,000) into the nucleus, but blocked the uptake of PE conjugates. This inhibition was reversed when a competing saccharide was introduced into the cytoplasm.  相似文献   

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Baculoviruses are one of the largest viruses that replicate in the nucleus of their host cells. During an infection the capsid, containing the DNA viral genome, is released into the cytoplasm and delivers the genome into the nucleus by a mechanism that is largely unknown. Here, we used capsids of the baculovirus Autographa californica multiple nucleopolyhedrovirus in combination with electron microscopy and discovered this capsid crosses the NPC and enters into the nucleus intact, where it releases its genome. To better illustrate the existence of this capsid through the NPC in its native conformation, we reconstructed the nuclear import event using electron tomography. In addition, using different experimental conditions, we were able to visualize the intact capsid interacting with NPC cytoplasmic filaments, as an initial docking site, and midway through the NPC. Our data suggests the NPC central channel undergoes large-scale rearrangements to allow translocation of the intact 250-nm long baculovirus capsid. We discuss our results in the light of the hypothetical models of NPC function.  相似文献   

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Nuclear pore complexes (NPCs) are large proteinaceous assemblies that provide the only known portals for exchanging macromolecules between the nucleus and cytoplasm. This includes the movement of small molecules and the selective, facilitated transport of large proteins and RNAs. Faithful, continuous NPC assembly is key for maintaining normal physiological function and is closely tied to proper cell division. This review focuses on the most outstanding issues involving NPC structure, assembly, and function.  相似文献   

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