Nucleolus proteins

The number and size of mitochondria indicate the level of energy metabolism and vary according to the condition of the fish (Ozemyuk, 1985 Savina, 1992), as does the level of nucleolus-protein biosynthesis (Arkhipchuk and Makarova, 1992). 

Nucleus The nucleus is separated from the cytosol by a double membrane, the nuclear envelope. The DNA is complexed with basic proteins (histones) to form chromatin fibers, the material from which chromosomes are made. A distinct RNA-rich region, the nucleolus, is the site of ribosome assembly. The nucleus is the repository of genetic information encoded in DNA and organized into chromosomes. During mitosis, the chromosomes are replicated and transmitted to the daughter cells. The genetic information of DNA is transcribed into RNA in the nucleus and passes into the cytosol where it is translated into protein by ribosomes. 

Like other cells, a neuron has a nucleus with genetic DNA, although nerve cells cannot divide (replicate) after maturity, and a prominent nucleolus for ribosome synthesis. There are also mitochondria for energy supply as well as a smooth and a rough endoplasmic reticulum for lipid and protein synthesis, and a Golgi apparatus. These are all in a fluid cytosol (cytoplasm), containing enzymes for cell metabolism and NT synthesis and which is surrounded by a phospholipid plasma membrane, impermeable to ions and water-soluble substances. In order to cross the membrane, substances either have to be very lipid soluble or transported by special carrier proteins. It is also the site for NT receptors and the various ion channels important in the control of neuronal excitability. 

A commonly used staining method for the cell nucleolus is based on silver nanoparticles [54], The proteins of the nucleolus, such as nucleolin, are known to have high affinity to silver ions due to their amino-terminal domain. Subsequent reduction leads to the formation of the silver nanoparticles stain. In spite of all the efforts, a general and definitive conclusion regarding the attraction between silver... 

Figure 7. A series of monoclonal antibodies raised against nuclear proteins. HeLa cells fixed with 4% paraformaldehyde were immunostained with monoclonal antibodies raised against nuclear proteins. The intracellular localization of these antigens are (a) dot inside the nucleolus, (b) whole nucleolus, (c) nuclear foci, (d) nucleoplasm, (e) the edge of the nucleus, (f) cytoplasm, (g) cytoskeleton, (h) plasma membrane, (i) mitochondria, (j) nucleus and cytoplasm, (k) nucleus and the paranuclear structure, and (1) paranuclear structure and nucleoplasm...

At last, nucleolin might play a specific role in telomeric replication and maintenance, as suggested by two types of data. First, it binds telomeric repeat (TTAGGG)n in vitro (Ishikawa et al, 1993 Pollice et al, 2000), with a marked preference for the single-stranded form. Secondly, it interacts in vitro and in vivo with hTERT (Khurts et al, 2004), the protein catalytic component of human telom-erase. This interaction takes place both in the cytoplasm and in the nucleolus, where it could promote the assembly of hTERT with the RNA subunit hTERC. As a conclusion, many data regarding the involvement of nucleolin in DNA replication are indirect and an experimental demonstration through knockdown or knockout studies is still awaited. 

Bose S, Basu M, Banerjee AK (2004) Role of nucleolin in human parainfluenza virus type 3 infection of human lung epithelial cells. J Virol 78 8146-8158 Bouche G, Caizergues-Ferrer M, Bugler B, Amalric F (1984) Interrelations between the maturation of a 100 kDa nucleolar protein and pre rRNA synthesis in CHO cells. Nucleic Acids Res 12 3025-3035 Bouche G, Gas N, Prats H, Baldin V, Tauber JP, Teissie J, Amalric F (1987) Basic fibroblast growth factor enters the nucleolus and stimulates the transcription of ribosomal genes in ABAE cells undergoing GO-Gl transition. Proc Natl Acad Sci U S A 84(19) 6770-6774. 

Pederson T (2002) Proteomics of the nucleolus more proteins, more functions Trends Biochem Sci 27 111-112... 

Eukaryotic ribosomal RNA is transcribed in the nucleolus by RNA polymerase I as a single piece of 45S RNA, which is subsequently deaved to yield 28S rRNA, 18S rRNA, and 5.8S rRNA. RNA polymerase III transcribes the 5S rRNA unit from a separate gene. TTie ribosomal subunits assemble in the nudeolus as the rRNA pieces combine with ribosomal proteins. Eukaryotic ribosomal subunits are 60S and 40S. They join during protein synthesis to form the whole SOS ribosome. 

Visible in the nuclei of most cells, especially those actively synthesising protein, is a nucleolus. It consists of a mass of incomplete ribosome particles and DNA molecules that code for ribosomal RNA this is the site of synthesis of the ribosomal subunits. 

Cellular RNAs vary widely in their size, structure, and lifespan. The great majority of them are ribosomal RNA (rRNA), which in several forms is a structural and functional component of ribosomes (see p.250). Ribosomal RNA is produced from DNA by transcription in the nucleolus, and it is processed there and assembled with proteins to form ribosome subunits (see pp.208, 242). The bacterial 16S-rRNA shown in Fig. A, with 1542 nucleotides (nt), is a component of the small ribosomae subunit, while the much smaller 5S-rRNA (118 nt) is located in the large subunit. 

The nucleus is not capable of synthesizing proteins. All of the nuclear proteins therefore have to be imported—the histones with which DNA is associated in chromatin, and also the so-called non-histone proteins (DNA polymerases and RNA polymerases, auxiliary and structural proteins, transcription factors, and ribosomal proteins). Ribosomal RNA (rRNA) already associates with proteins in the nucleolus to form ribosome precursors. 

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... 

FIGURE 26-22 Processing of pre-rRNA transcripts in vertebrates. In step (T), the 45S precursor is methylated at more than 100 of its 14,000 nucleotides, mostly on the 2 -OH groups of ribose units retained in the final products. (5) A series of enzymatic cleavages produces the 18S, 5.8S, and 28S rRNAs. The cleavage reactions require RNAs found in the nucleolus, called small nucleolar RNAs (snoRNAs), within protein complexes reminiscent of spliceosomes. The 5S rRNA is produced separately. 

Molecular communication between the nucleus and the cytosol requires the movement of macromolecules through nuclear pores. RNA molecules synthesized in the nucleus are exported to the cytosol. Ribosomal proteins synthesized on cytosolic ribosomes are imported into the nucleus and assembled into 60S and 40S ribosomal subunits in the nucleolus completed subunits are then exported back to the cytosol. A variety of nuclear proteins (RNA and DNA polymerases, histones, topo-isomerases, proteins that regulate gene expression, and so forth) are synthesized in the cytosol and imported into the nucleus. This traffic is modulated by a complex system of molecular signals and transport proteins that is gradually being elucidated. 

As is indicated in Fig. 28-15, transcription is thought to occur from the loops of DNA that form the nucleolar organizing region. The 100-kDa nucleolin, the major protein of the nucleolus, binds to the non-transcribed spacer sequences in the DNA.529-530 It also binds to the newly formed transcripts, as do various proteins that enter the nucleus from the cytoplasm.524531 More than 270 proteins, many of which participate in synthesis of ribosomes, have been detected in the nucleolus.5313 Some of these proteins, acting together with the snoRNAs discussed in the next section, catalyze hydrolytic cleavage of the pre-rRNA molecules. For completion of pre-ribosomal particles additional protein molecules enter the nucleolus and associate with the pre-rRNA particles, then diffuse out of the nucleus. 

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