Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nuclear Pore Complex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1990

Correlation between structure and mass distribution of the nuclear pore complex and of distinct pore complex components.

Nuclear pore complexes (NPCs) prepared from Xenopus laevis oocyte nuclear envelopes were studied in "intact" form (i.e., unexposed to detergent) and after detergent treatment by a combination of conventional transmission electron microscopy (CTEM) and quantitative scanning transmission electron microscopy (STEM). In correlation-averaged CTEM pictures of negatively stained intact NPCs and of distinct NPC components (i.e., "rings," "spoke" complexes, and "plug-spoke" complexes), several fine structural features arranged with octagonal symmetry about a central axis could reproducibly be identified. STEM micrographs of unstained/freeze-dried intact NPCs as well as of their components yielded comparable but less distinct features. Mass determination by STEM revealed the following molecular masses: intact NPC with plug, 124 +/- 11 MD; intact NPC without plug, 112 +/- 11 MD; heavy ring, 32 +/- 5 MD; light ring, 21 +/- 4 MD; plug-spoke complex, 66 +/- 8 MD; and spoke complex, 52 +/- 3 MD. Based on these combined CTEM and STEM data, a three-dimensional model of the NPC exhibiting eightfold centrosymmetry about an axis perpendicular to the plane of the nuclear envelope but asymmetric along this axis is proposed. This structural polarity of the NPC across the nuclear envelope is in accord with its well-documented functional polarity facilitating mediated nucleocytoplasmic exchange of molecules and particles.

Animals↗
PubMed1992

Molecular trafficking across the nuclear pore complex.

The nuclear pore complex is the gateway for protein and RNA transport between the cytoplasm and nucleus. Recent work has characterized signals and components involved in nuclear import of macromolecules and has described mechanisms for transport regulation. Advances in understanding the structure of the pore complex are starting to provide a framework for interpreting the biochemistry of nuclear import. Information on the export of RNA from the nucleus is only beginning to emerge.

Animals↗
PubMed1991

Toward a more complete 3-D structure of the nuclear pore complex.

The nuclear pore complex (NPC) is a large supramolecular assembly embedded in the double-membraned nuclear envelope (NE) that plays a pivotal role in the exchange of macromolecules and particles between the nucleus and the cytoplasm. Applying various methods of sample preparation to Xenopus laevis whole nuclei and isolated NEs in combination with conventional transmission electron microscopy and digital image processing, we have characterized several distinct components of the NPC, including massive cytoplasmic and more tenuous nuclear rings, NPCs devoid of their cytoplasmic or both rings, and prominent "knobs" that protrude from the periphery of the NPC proper into the lumen of the NE. Moreover, by quick freezing/freeze drying/rotary metal shadowing isolated NEs, we have visualized two distinct types of NPC-associated filaments: (1) eight short, highly twisted filaments that project from the cytoplasmic ring and sometimes collapse into short cylinders; and (2) eight long, thin filaments that protrude from the nuclear ring and whose ends join to form a distal ring centered above the NPC such that the assembly resembles a "fishtrap." These nuclear fishtraps are sensitive to divalent cations: removal unfolds them and addition reforms them. The significance of these various structural components in terms of current NPC models is discussed, and the emerging asymmetry of the NPC relative to its nuclear and cytoplasmic face is stressed.

Actins↗
PubMed1992

Purification of a glucose-binding protein from rat liver nuclei. Evidence for a role in targeting of nuclear mRNP to nuclear pore complex.

A nuclear carbohydrate-binding protein with a molecular mass of 67 kDa (CBP67), which is specific for glucose residues, was purified to essential homogeneity from rat liver nuclear extracts. This protein could also be isolated from nuclear ribonucleoprotein (RNP) complexes by extraction in the presence of 0.6 M or 2 M NaCl, but it was absent in polysomal RNP complex. The binding of the purified protein, which has an isoelectric point of 7.3, to glucose-containing glycoconjugates depends on the presence of Ca2+ and Mg2+. Using closed nuclear envelope vesicles as a system to study nuclear transport of RNA, it was shown that both entrapped polysomal mRNA and nuclear RNA precursors are readily exported from the vesicles in an ATP-dependent manner. The transport was unidirectional and strongly promoted by the poly(A) segment attached to these RNAs. In contrast, nuclear RNP complexes entrapped into the vesicles together with glucose-conjugated bovine serum albumin or nucleoplasmin, or bird nest glycoprotein, were not exported into the extravesicular space. However, transport of nuclear RNP complexes could be achieved in the presence of glucose or after co-addition of a glucose-recognizing lectin from Pellina semitubulosa. In Western blots, radioiodinated CBP67 binds to an 80-kDa polypeptide both in isolated rat liver nuclear envelopes and pore-complex laminae. From these results we postulate that CBP67 may direct nuclear RNP complexes to the nuclear pore.

Animals↗
PubMed1989

Quick-freeze, deep-etch visualization of the nuclear pore complex.

We have visualized the nuclear pore complex (NPCx) three-dimensionally by quick-freeze, deep etching and suggest that NPCx is composed of four rings and associated filaments. The rings were located at the cytoplasmic side, at the nucleoplasmic side, and at the pore waist as well. Some of the filaments emanated toward the cytoplasm, some sprawled over the cytoplasmic face of the nuclear membrane, and some intervened the rings. The emanating filaments were considered to be vimentin filaments judging from the replica and thin-sectioned image.

Freeze Etching↗
PubMed1992

A new family of yeast nuclear pore complex proteins.

We have identified a novel family of yeast nuclear pore complex proteins. Three individual members of this family, NUP49, NUP100, and NUP116, have been isolated and then characterized by a combination of molecular genetics and immunolocalization. Employing immunoelectron and immunofluorescence microscopy on yeast cells, we found that the binding of a polyspecific monoclonal antibody recognizing this family was predominantly at the nuclear pore complexes. Furthermore, the tagging of NUP49 with a unique epitope enabled the immunolocalization of this protein to the nuclear pore complex by both fluorescence and electron microscopy. DNA sequence analysis has shown that the amino-terminal regions of NUP49, NUP100, and NUP116 share repeated "GLFG" motifs separated from each other by glutamine, asparagine, serine and threonine rich spacers. All three proteins lack a repetitive domain found in the two precisely described yeast nuclear pore complex proteins. Only NUP49 is essential for cell viability. NUP116-deficient cells grow very slowly and are temperature sensitive, whereas the lack of NUP100 has no detectable phenotype. NUP100 and NUP116 are homologous over their entire lengths. Interestingly, NUP100 and NUP116 are both flanked by a histidine tRNA gene and a transposon element suggesting that they may have arisen by gene duplication. We propose that subfamilies of pore complex proteins can be defined by their characteristic combinations of different modular domains.

Amino Acid Sequence↗
PubMed1989

Organization of the nuclear pore complex in Saccharomyces cerevisiae.

Fractions enriched for nuclear pore complexes (NPCs) have been isolated from Saccharomyces cerevisiae. The sequential extraction of nuclei with detergent, nucleases, and salt reveals an organization of the yeast NPC similar to other eukaryotes. Yeast NPCs contain a 30-nm "ring" structure not previously described in other organisms. This structure appears to organize 10-nm filaments into an assembly which exhibits an eight-fold rotational symmetry. Some proteins in the NPC fraction are capable of forming intermediate-sized filaments. These studies suggest that some component of the nuclear pore complex organizes an interaction between nuclear and cytoplasmic networks of intermediate filaments.

Microscopy, Electron↗
PubMed1975

Isolation of nuclear pore complexes in association with a lamina.

Nuclear pore complexes have been isolated in association with a 150 A thick lamina by detergent and salt fractionation of nuclear envelopes from rat liver. The pore complexes exhibit characteristic morphology and appear to be attached in a highly specific orientation to the lamina, which extends over relatively large areas. The pore complex-lamina fraction is composed of three major and several minor polypeptides with little or no DNA, RNA, or phospholipid. It is suggested that the association of the pore complexes and the lamina reflects the structural arrangement of the nuclear periphery in vivo.

Animals↗
PubMed1971

Formation and distribution of nuclear pore complexes in interphase.

The possibility of nuclear pore formation in the interphase nucleus was investigated in control and phytohemagglutinin (PHA) stimulated lymphocytes by the freeze-etching technique. 48 hr after the addition of PHA, the newly formed blasts which had not as yet divided had at least twice the number of pores per nucleus as controls. This clearly demonstrates that in lymphocytes nuclear pore formation can take place during interphase. It has generally been assumed that the distribution of nuclear pore complexes in somatic animal cells is random. However, we have utilized freeze etched rat kidney cells and a computer program to evaluate pore distribution. We find a minimum pore center-to-center spacing of approximately 1300 A and multiples thereof with high frequency. This is strong evidence for a nonrandom distribution of nuclear pores. The nonrandomness may be related to an underlying chromosomal organization in interphase. Using three criteria for identifying prospective pore sites (membrane specialization, nonrandomness, and alteration of heterochromatin distribution), we have found forming pores in sectioned material from cultured human melanoma cells. While nuclear pore formation may take place in conjunction with reformation of the nuclear membrane, a mechanism also exists for their formation during interphase.

Animals↗
PubMed1977

Nuclear pore complexes. Elimination and reconstruction during mitosis.

Nuclear structures similar to those of the nuclear pore complex were found on chromosomes. This finding indicates that part of the pore complex is retained by the chromosomes through mitosis in the absence of the nuclear membrane. The formation of approximately the same number of pore complexes in the presence and absence of protein synthesis during the first 4 h after mitosis proves the reassembly rather than new synthesis of the pore complex. The structure of pore complexes reconstructed in the absence of protein synthesis cannot be distinguished from the structure of those of control cells.

Cell Nucleus↗
PubMed1988

Filamentous cross-bridges link intermediate filaments to the nuclear pore complexes.

Intermediate filament-nuclear matrix interactions were studied in cultured rat ventral prostate cells and isolated rat uterine epithelial cells. Cytokeratin filaments were identified by immunoelectron microscopy. In addition to conventional thin section of Triton X-100 treated cells, subcellular residues composed of intermediate filaments and nuclear matrix were critical-point dried and platinum-carbon replicated. The results demonstrate the presence of a previously unrecognized type of filamentous cross-bridges that link intermediate filaments to the nuclear pore complexes.

Animals↗
PubMed1989

Interactions and structure of the nuclear pore complex revealed by cryo-electron microscopy.

Nuclear pore complexes (NPCs) play a central role in mediating nucleocytoplasmic transport and exchange processes in eukaryotic cells. The arrangement and interactions of NPCs within amphibian nuclear envelopes have been studied using cryo-electron microscopy of unfixed and frozen hydrated specimens. The nuclear lamina in Necturus forms an orthogonal network with crossover distances which vary between 1,600 and 4,000 A and which may be related to the basic filament repeat of lamins. Furthermore, the NPCs are attached randomly within the confines of the lamin network, presumably by their nucleoplasmic rings. Image analysis of edge-on and en face projections of detergent-extracted NPCs has been combined with data on the coaxial thin rings to provide a quantitative evaluation of the triple ring model of NPC architecture proposed previously (Unwin, P. N. T., and R. Milligan. 1982. J. Cell Biol. 93:63-75). Additional details of the complex have been visualized including an intimate association of the inner spoke domains as an inner spoke ring, extensive domains within the spokes and coaxial thin rings, and interestingly, a central channel-like feature. Membrane-associated NPCs and detergent-extracted NPCs both possess peripherally located radial arms resulting in an effective diameter of approximately 1,450-1,500 A. In projection, the radial arms possess approximate mirror symmetry suggesting that they originate from both sides of the assembly. Moreover, membrane-associated NPCs are asymmetric at most radii and right-handed as viewed from the cytoplasm; detergent-extracted NPCs appear to be symmetric and have approximately 822 symmetry. Taken together, the data suggests that the framework of membrane-associated NPCs is perturbed from a symmetrical configuration, either during isolation of nuclei or by interactions with the lamina and the nuclear envelope in vivo. However, detergent extraction of nuclei appears to result in a more symmetrical alignment of components in apposing halves of the assembly.

Animals↗
PubMed1990

The NUP1 gene encodes an essential component of the yeast nuclear pore complex.

Monoclonal antibodies generated against a family of related nuclear pore complex proteins (nucleoporins) from rat liver nuclei cross-react with several proteins in the yeast S. cerevisiae and show punctate nuclear envelope staining similar to the pattern seen in mammalian cells. We have cloned a gene encoding one of these proteins (NUP1) and have confirmed the localization of the NUP1 protein to the pore complex by immunofluorescence, using an epitope-tagged construct to differentiate it from other members of this family. The NUP1 protein is essential for cell viability, and overexpression from the yeast GAL10 promoter prevents further cell growth. The central domain of NUP1 consists of a series of degenerate repeats similar to those found in the nucleoskeletal protein NSP1, a protein that cross-reacts with monoclonal antibodies against NUP1. We propose that the repetitive domain is a feature common to the nucleoporins.

Amino Acid Sequence↗
PubMed1992

Architecture and design of the nuclear pore complex.

A three-dimensional analysis of the nuclear pore complex reveals the underlying, highly symmetric framework of this supramolecular assembly, how it is anchored in the nuclear membrane, and how it is built from many distinct, interconnected subunits. The arrangement of the subunits within the membrane pore creates a large central channel, through which active nucleocytoplasmic transport is known to occur, and eight smaller peripheral channels that are probable routes for passive diffusion of ions and small molecules.

Animals↗
PubMed1992

O-linked glycoproteins of the nuclear pore complex interact with a cytosolic factor required for nuclear protein import.

Mediated import of proteins into the nucleus requires cytosolic factors and can be blocked by reagents that bind to O-linked glycoproteins of the nuclear pore complex. To investigate whether a cytosolic transport factor directly interacts with these glycoproteins, O-linked glycoproteins from rat liver nuclear envelopes were immobilized on Sepharose beads via wheat germ agglutinin or specific antibodies. When rabbit reticulocyte lysate (which provides cytosolic factors required for in vitro nuclear import) was incubated with the immobilized glycoproteins, the cytosol was found to be inactivated by up to 80% in its ability to support mediated protein import in permeabilized mammalian cells. Inactivation of the import capacity of cytosol, which was specifically attributable to the glycoproteins, involves stoichiometric interactions and is likely to involve binding and depletion of a required factor from the cytosol. This factor is distinct from an N-ethylmaleimide-sensitive receptor for nuclear localization sequences characterized recently since it is insensitive to N-ethylmaleimide. Cytosol inactivation is suggested to be caused by at least two proteins of the glycoprotein fraction, although substantial capacity for inactivation can be attributed to protein bound by the RL11 antibody, consisting predominantly of a 180-kD glycosylated polypeptide. Considered together, these experiments identify a novel cytosolic factor required for nuclear protein import that directly interacts with O-linked glycoproteins of the pore complex, and provide a specific assay for isolation of this component.

Animals↗
PubMed1992

Nuclear protein import is inhibited by an antibody to a lumenal epitope of a nuclear pore complex glycoprotein.

Gp210 is a major transmembrane glycoprotein associated with the nuclear pore complex that is suggested to be important for organizing pore complex architecture and assembly. A mouse monoclonal IgG directed against an epitope in the lumenal domain of rat gp210 was expressed in cultured rat cells by microinjection of mRNA prepared from a hybridoma cell line. The expressed IgG, which becomes assembled into a functional antibody in the lumen of the endoplasmic reticulum, bound to the nuclear envelope in vivo. Expression of anti-gp210 antibody in interphase cells specifically reduced approximately fourfold the mediated nuclear import of a microinjected nuclear protein (nucleoplasmin) coupled to gold particles. The antibody also significantly decreased nuclear influx of a 10-kD dextran by passive diffusion. This transport inhibition did not result from removal of pore complexes from nuclear membranes or from gross alterations in pore complex structure, as shown by EM and immunocytochemistry. A physiological consequence of this transport inhibition was inhibition of cell progression from G2 into M phase. Hence, binding of this antibody to the lumenal side of gp210 must have a transmembrane effect on the structure and functions of the pore complex. These data argue that gp210 is directly or indirectly connected to pore complex constituents involved in mediated import and passive diffusion.

Animals↗
PubMed1992

Regulation of macromolecular traffic mediated by the nuclear pore complex.

A sophisticated selective mechanism that regulates nuclear-cytoplasmic traffic has evolved in eukaryotes which circumvents the formidable barrier presented by the nuclear envelope. The sites of RNA and protein exchanges are the nuclear pore complexes (NPCs), 125 MDa supramolecular assemblies inserted into the envelope (see recent reviews by Dingwall, 1991; Goldfarb and Michaud, 1991; Miller et al., 1991; Nigg et al., 1991). In this article, the role NPCs play in regulating intracellular macromolecular traffic will be discussed.

Animals↗