Nuclear pore complex

Expoitins are transport receptors at the nuclear pore complex needed for the selective export of proteins from the nucleus into the cytoplasm. They recognize nuclear export signal sequences of cargo proteins. 

The nuclear pore complex, located in the nuclear envelope, contains more than 50 proteins. It allows diffusion of small proteins between cytoplasm and nucleoplasm. Larger molecules (>50kD) are selectively transported by an energy-dependent mechanism. 

Rout, M. P., Aitchinson, J. D., Suprapto, A., Hjertaas, K., Zhao, Y., and Chait, B. T. (2000). The yeast nuclear pore complex composition, architecture, and transport mechanism. J. Cell Biol. 148, 635-651. 

Ran (the Ras-related nuclear protein) is the major regulator of nucleo-cytoplas-mic transport [134] across the nuclear pore complex (NPC). Like other small Ras-like GTP-binding proteins, it switches between a GTP- and a GDP-bound form by GTP-hydrolysis and nucleotide exchange [135]. In contrast to its relatives, Ran does not undergo posttranslational modification. 

The recycling process of Ran between its GDP and GTP complexed state is supported by another class of Ran-binding proteins, which support GTP-hydro-lysis by RanGAP and are either soluble proteins [ 143] or part of the nuclear pore complex [144]. 

Bustamante JO, Liepers A, Prendergast RA, Hanover JA, Oberliethner H. Patch clamp and atomic force microscopy demonstrate TATA-binding protein (TBP) interactions with the nuclear pore complex. JMembrane Biol 1995 146 X263-X272. 

The nuclear envelope is composed of the nuclear membranes (inner and outer), the nuclear lamina, and the nuclear pore complexes. The inner and outer nuclear membranes are connected at the nuclear pore sites and enclose a flattened sac... 

Nuclear pore complex protein nu Accession number swissprot P52948... 

The nucleus is surrounded by the nuclear envelope, which takes on a lumenal structure connected to the endoplasmic reticulum. The transport of proteins into (and out of) the nucleus occurs through the nuclear pore complex (NPC), a large complex composed of more than 100 different proteins (Talcott and Moore, 1999). Because NPC forms an aqueous pore across the two membranes, small proteins less than 9 nm in diameter can pass through it simply by diffusion. However, most of the transports of both proteins and RNAs are mediated by an active transport mechanism. It is now clear that there is heavy traffic through the NPC in both directions. Proteins are not only imported into the nucleus but also actively exported from it as well. There are many reasons for nuclear export. One reason is to send some shuttle proteins back after their import another is for some viral proteins to export their replicated genomes outside the nucleus. 

Talcott, B., and Moore, M. (1999). Getting across the nuclear pore complex. Trends Cell Biol. 9, 312-318. 

Mahajan, R., Delphin, C., Guan, T., Geeace, L., and Melchior, F. A small ubiquitin-related polypeptide involved in targeting RanGAPl to nuclear pore complex protein RanBP2, Cell, 1997, 88, 97-107. 

Matunis, M. j., Coutavas, E., and Blobel, G., a novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAPl between the cytosol and the nuclear pore complex,/. Cell. Biol., 1996, 135, 1457. 

Colin M, Moritz S, Fontanges P, et al. The nuclear pore complex is involved in nuclear transfer of plasmid DNA condensed with an oligolysine-RGD peptide containing nuclear localisation properties. J Biol Chem 2001 8(21) 1643-1653. 

It is believed that binding of RanGAPl to tbe nuclear pore complex facilitates nuclear... 

Matunis MJ, Wu J, Blobel G (1998) SUMO-1 modification and its role in targeting the Ran GTPase-activating protein, RanGAPl, to the nuclear pore complex. J Cell Biol 140 499-509... 

Pante N, Aebi U (1996) Molecular dissection of the nuclear pore complex. Crit Rev Biochem Mol Biol 31 153-199... 

The role of the nuclear pore complex in adenovirus DNA entry. Embo J, 1997. 16(19) 5998-6007. 

O-GlcNAc s subcellular localization in rat hepatocytes established that it is highly concentrated at the nuclear envelope, particularly at the nuclear pore complex, but is also abundant and widespread within chromatin (Holt and Hart, 1986). Aside from the biosynthetic intermediates,... 

The nuclear envelope is perforated with huge macromolecular assemblies of 30 different proteins that form nuclear pore complexes with a central channel of 25-30 nm in diameter. This channel allows proteins smaller than 30 kDa to passively traverse the outer and inner nuclear membranes. Larger proteins are actively transported across the nuclear envelope and contain nuclear localization signal (NLS) sequence motifs. These signals consist of one or two clusters of four or five basic residues localized usually within the polypeptide chain. The import of proteins with NLS through the channel is facilitated by the carrier heterodimer of importin-a ( > (Gorlich and Kutay 1999 Pemberton and Paschal... 

Figure 27-7 Native nuclear lamina of Xenopus oocytes. Freeze-dried metal-shadowed nuclear envelope extracted with Triton X-100, revealing the nuclear lamina meshwork partially covered with arrays of nuclear pore complexes. Inset, relatively well-preserved area of the meshwork of nearly orthogonal filaments from which pore complexes have been mechanically removed. Bar, 1 pm. From Aebi et al.121...

Figure 11.1 The intracellular trafficking pathway of plasmid DNA complexed by poly cationic lipid (lipoplex). Critical steps are indicated by numbers (1) endocytosis, sorting and recycling via vesicular compartments comprising the early (EE) and sorting endosomes (2) entrapment and degradation in the late-endosomes (LE) and lysosomes (3) destabilization of the endo-lysosomal membrane and release into the cytosol, (the precise location of this step is not known) (4) diffusion toward the nuclear pore complex (NPC) and degradation in the cytoplasm, and (5) nuclear translocation across the NPC.

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