Nuclear pore complex components

The increase in nuclear cyclin B/CDKl activity promotes phosphorylation of nuclear substrates that are necessary for mitosis, such as nuclear envelope breakdown, spindle formation, chromatin condensation, and restmcturing of the Golgi and endoplasmic reticulum (85, 86). Numerous cyclin B/CDKl substrates have been dehned, which include nuclear lamins, nucleolar proteins, centrosomal proteins, components of the nuclear pore complex, and microtubule-associated proteins (87-89). Cyclin B/CDKl complexes also phosphorylate MCM4 to block replication of DNA, the TFIIH subunit of RNA polymerase II to inhibit transcription, and the ribosomal S6 protein kinase to prevent translation during mitosis (90-92). 

Devos, D., S. Dokudovskaya, F. Alber, R. Williams, B. T. Chait, A. Sali, and M. P. Rout. 2004. Components of coated vesicles and nuclear pore complexes share a common molecular architecture. PLoS Biol 2 E380. 

Although in higher eukaryotes nuclear pore complexes have not been isolated free of peripheral lamina and other karyoskeletal components, much is currently known about their polypeptide structure. A glycoprotein, gp210 (Gerace et al, 1982 Wozniak et al, 1989 Greber et al, 1990), was the first polypeptide to be identified as a pore complex component by immunoelectron microscopy (Gerace... 

Reichelt, R., Holzenburg, A., Buhle, E. L. Jr., Jamik, M., Engel, A., and Aebi, U. (1990). Correlation between structure and mass distribution of the nuclear pore complex and of distinct pore complex components. J. Cell BioL 110,883-894. 

Davis, L. 1., and Fink, G. R. (1990). The NUPl gene encodes an essential component of the yeast nuclear pore complex. Cell Cambridge, Mass.) 61,965-978. 

Reassembly of nuclei can be followed most easily by phase-contrast microscopy. During the course of the assembly reaction clusters of chromosomes will be observed to fuse into single masses of chromatin, which will eventually become spherical in shape as decondensation progresses. At this point, thin-section electron microscopy should reveal the presence of a continuous double membrane studded with nuclear pore complexes surrounding each chromatin mass. Assembly of individual nuclear envelope components such as nuclear lamins or nuclear pore complex proteins can best be analyzed by immunofluorescence microscopy (Burke and Gerace, 1986). This is performed as follows. 

Figure 10 Components of the nuclear pore complex. Structures are available from the PDB and EMDB for some of the components of the nuclear core complex. The individual proteins and small subassemblies shown in ribbon representation are from six PDB entries that provide atomic-level information from X-ray (4GQ2, 3UKY, 4FHN, 3TKN, 4GQ1) or nuclear magnetic resonance spectroscopy (2EC1) studies. The three larger subassemblies drawn as surfaces have been analyzed by cryo-electron microscopy (EMD-5152, EMD-1097) or cryo-electron tomography (EMD-1394).

The final principal component of the cell is the nucleus. This is located in the center of the cell and is surrounded by a double membrane, the outer layer being derived from the ER of the cytoplasm and the inner layer coming from the nucleus itself. The two leaflets of the double membrane are fused in places, producing nuclear pores that enable the transfer of macromolecules from the cytoplasm to the nucleus. Two important components of the nucleus are chromatin and the nucleolus. Chromatin represents polymers of DNA complexed with protein. The nucleolus is a complex substructure, composed of ribonucleoprotein granules, that controls the synthesis of RNA destined to form the ribosomes of the cytoplasm. Cells engaged heavily in protein synthesis have... 

Newly synthesized mRNA emerges from the nuclear pores as nucleoprotein complexes containing as many as ten different proteins. A major component is a 78-kDa polypeptide thought to be associated with the poly(A) tail. These ribonucleoproteins are sometimes stored for long periods of time, for example, in mature seed embryos and in amphibian oocytes.5753/674 They may also travel rapidly for long distances, e.g., down nerve axons675 or from cell to cell in plants via transport in the phloem.676... 

Imamoto, N, Shinamoto, T., Takao, T.. Tachibana. T., Kose, S., Matsubae, M., Sekimoto, T., Shimonishi, Y., and Yoneda, Y. (1995a). In vivo evidence for involvement of a 58kDa component of nuclear pore targeting complex in protein import. EMBO J. 14, 3617-3626. 

The nucleus of eukaryotic cells is a very complex structure, containing various components. It is separated from the rest of the cell by two membranes named the nuclear envelope. At regular intervals, the two membranes of the nuclear envelope form pores with a diameter of around 90 nm. These pores regulate flux of macromolecules to and from the cytoplasm. Inside the nucleus is located the nucleolus, which acts to produce ribonucleic acid (RNA), which is the first step for ribosome synthesis. 

---