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Results for “Nuclear Pore Complex”

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At least 379 records · Page 21Linked to original sources
PubMed1996

An antibody against a glycosylated integral membrane protein of the Xenopus laevis nuclear pore complex: a tool for the study of pore complex membranes.

We have recently described a monoclonal antibody (X222) which localizes at pore complexes in Xenopus oocytes and immunoblots a protein under nonreducing conditions with an apparent molecular mass of 215 kDa (Cordes, Gajewski, Stumpp, Krohne, Differentiation 58, 307-312, (1995)). Under reducing conditions, this antigen decreased from the previously reported 215 kDa to 200 kDa. Since this protein binds to the lectin concanavalin A (Con A), we now refer to it as gp200. In addition to Con A binding, Xenopus gp200 has several other features in common with the mammalian pore membrane protein gp210. On nuclear envelopes extracted with Triton X-100, gp200 was localized on the lateral walls of pores, a subdomain covered in native nuclear envelopes by the lipid bilayer. In mitotic extracts of Xenopus eggs gp200 was exclusively recovered in the membrane fraction. Treatment of oocyte membranes with urea and proteases indicated that gp200 is an integral membrane protein with the bulk of its mass located within the membrane lumen. In Xenopus oocyte nuclei gp200 is the major Con A binding protein. The new monoclonal antibody X222 has allowed us to characterize the first integral membrane protein, gp200, of the Xenopus pore complex.

Animals↗
PubMed1995

Differential mitotic phosphorylation of proteins of the nuclear pore complex.

During each cell cycle, the nucleus of higher eukaryotes undergoes a dramatic assembly and disassembly. These events can be faithfully reproduced in vitro using cell-free extracts derived from Xenopus eggs. Such extracts contain three major N-acetylglucosaminylated proteins, p200, p97, and p60. All three become assembled into reconstituted nuclear pores. Here we show that p200, p97, and p60 exist in eggs in soluble high molecular mass complexes of 1000, 450, and 600 kDA, respectively. The bulk of p60 is stably associated with proteins of 58 and 54 kDa, while p200 is associated with a fraction of p60 in a separate complex lacking p58 and p54. Upon examining the behavior of these proteins in the cell cycle, we find that p200 and p97 are highly phosphorylated at mitosis, both in vivo and in vitro. Moreover, in extracts that cycle between interphase and mitosis, p200 and p97 are specifically phosphorylated at mitosis. Corresponding with their mitotic phosphorylation, both p200 and p97 are specific substrates for purified mitotic Cdc2 kinase, whereas nucleoporin p60 is not. Analysis indicates that the size of the complexes containing the pore N-acetylglucosamine glycoproteins does not change during mitosis, suggesting that such complexes represent stable multicomponent modules into which the nucleus disassembles at mitosis.

Animals↗
PubMed1998

The nuclear import factor p10 regulates the functional size of the nuclear pore complex during oogenesis.

Previtellogenic, stage-1 Xenopus oocytes produce mainly 5S and tRNA, whereas vitellogenic oocytes, stages 2-6, synthesize predominantly 18S and 28S rRNA. Using nucleoplasmin-coated gold as a transport substrate, it was determined that the shift in synthesis from small to large RNAs during oogenesis is accompanied by an increase in both the rates of signal-mediated nuclear import and the functional size of nuclear pores. It was observed that, despite the reduction in transport capacity, gold still accumulated at the cytoplasmic surface of the pores in stage-1 oocytes. This suggested that transport in these cells is limited by translocation factors, rather than by cytoplasmic binding factors. Analysis of extracts prepared from stage-1 and vitellogenic oocytes revealed that the transport factor p10 is more abundant in stage-1 cells. Microinjection of purified p10 into stage-2 oocytes reduced the nuclear import of large gold particles to the level observed in stage-1 cells. It is concluded that p10 can modulate transport through the pores by regulating the functional size of the central transporter element.

Animals↗
PubMed1995

Autoantibodies against constituents of nuclear pore complexes in patients with primary biliary cirrhosis and autoimmune hepatitis.

Sera obtained from patients with autoimmune liver disease were screened in indirect immunofluorescence microscopy for the presence of autoantibodies. Patients' sera, which strongly stained nuclei (ANA) with peripheral accentuation, were used for further experiments to define the corresponding antigen(s). Nuclei and nuclear subfractions were isolated from HeLaS3 cells and used as antigen source. Immunoblotting experiments were performed after separation of nuclear proteins by one- and two-dimensional polyacrylamide gel electrophoresis. Some ANA positive sera recognized the nuclear protein with molecular mass of approximately 200 kDa. Further analysis revealed that the patients' sera reacted with gp210, an integral protein of the nuclear pores. The incidence and clinical significance of these antibodies is discussed.

Autoantibodies↗
PubMed2000

Pore relations: nuclear pore complexes and nucleocytoplasmic exchange.

NPCs are the sole sites of exchange between the nucleus and cytoplasm. A large family of transport factors carry cargo between the nucleus and cytoplasm through the NPC. The NPC is a huge symmetric octagonal structure comprised of dozens of NUPs. NUPs make many contacts with surrounding structures, including the NE, the cytoplasm and nuclear interior. A subset of NUPs contain repeated peptide motifs that serve as docking sites for transport factors. The directionality of transport is determined by the transport factor, and its interactions with the small GTPase Ran and NUPs. Very little is known about how the NPC mediates transport, NPC assembly and the NPC's role in regulating transport, but these areas of research are beginning to emerge.

Animals↗
PubMed2005

Importin-alpha promotes passage through the nuclear pore complex of human immunodeficiency virus type 1 Vpr.

Viral protein R (Vpr) of human immunodeficiency virus type 1 has potent karyophilic properties, but details of the mechanism by which it enters the nucleus remain to be clarified. We reported previously that two regions, located between residues 17 and 34 (alphaH1) and between residues 46 and 74 (alphaH2), are indispensable for the nuclear localization of Vpr. Here, we reveal that a chimeric protein composed of the nuclear localization signal of Vpr, glutathione S-transferase, and green fluorescent protein was localized at the nuclear envelope and then entered the nucleus upon addition of importin-alpha. An in vitro transport assay using a series of derivatives of importin-alpha demonstrated that the carboxyl terminus was required for this nuclear import process. We also showed that Vpr interacts with importin-alpha through alphaH1 and alphaH2; only the interaction via alphaH1 is indispensable for the nuclear entry of Vpr. These observations indicate that importin-alpha functions as a mediator for the nuclear entry of Vpr.

Cell Nucleus↗