RRNA synthesis

A strong link between the phosphorylation of nucleolin, its proteolysis and the production of ribosomal RNA has been observed (Bouche et al, 1984 Bourbon et al, 1983 Warrener and Petryshyn, 1991). The inhibition of proteolysis using leupeptin leads to a lower rRNA transcription in an in vitro transcription system (Bouche et al, 1984). In another series of experiments, the injection of nucleolin antiserum leads to 2-3.5 fold stimulation of pre-rRNA synthesis in Chironomus tentans salivary glands (Egyhazi et al, 1988), although it was not clearly demonstrated that these antibodies blocked specifically the homolog of nucleolin in this species. A model was proposed based on these observations where nucleolin was... 

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. 

Synthesis of Ribosomal Proteins Is Coordinated with rRNA Synthesis... 

Within bacterial cells the assembly of ribosomes is coupled to rRNA synthesis and requires only 1-2 minutes.115 In the laboratory both the 30S ribosomal subunits116 and the 50S subunits117-121 of E. coli can be completely dissociated into individual protein and RNA molecules and can be reconstituted in a functional form. This is true for both natural 16S or 23S RNA or for RNAs prepared by in vitro transcription. In these reassembly experiments, which were pioneered by Nomura,116 it was found that the order of addition of the protein is important. Some proteins bind... 

As stated earlier, rRNA synthesis is usually maintained at a rate proportional to the gross rate of protein synthesis. In a normal wild-type cell, when protein synthesis is limited (e.g., by amino acid availability), M. Cashel and J. Gallant have shown that the ppGpp concentration rises rapidly from about 50 pM to 500 /uM (fig. 30.16). Concomitantly, rRNA synthesis ceases abruptly. This is part of the phenotype known as the stringent response First, amino acid deprivation or other factors that slow down protein synthesis provoke an increased rate of accumulation of ppGpp thisin turn leads to an inhibition of rRNA synthesis. 

Schematic diagram of ppGpp synthesis and the hypothesized mechanism for its action. ppGpp is synthesized on the ribosome when there is a peptidyl-tRNA on the P site of the ribosome and uncharged tRNA on the A site. The ppGpp probably inhibits rRNA synthesis by complexing with the RNA polymerase.

The observations on ppGpp s role in rRNA synthesis show that this nucleotide is an important control factor regulating rRNA synthesis, but it does not eliminate the possibility that other factors also affect the level of rRNA. In vivo and in vitro evidence indicates that the inhibitory effect of ppGpp on transcription extends to most tRNA and riboso-mal protein genes. Ribosomal protein gene expression also appears to be regulated at the translational level. 

S rRNA Synthesis in Frogs Requires a Regulatory Protein... 

Dennis, P. P., Ehrenberg, M., and Bremer, H. (2004). Control of rRNA synthesis in Escherichia coli A systems biology approach. Microbiol. Mol. Biol. Rev. 68, 639—668. 

The nucleus stores the cell s genetic information as DNA in chromosomes. It is bounded by a double membrane but pores in this membrane allow molecules to move in and out of the nucleus. The nucleolus within the nucleus is the site of ribosomal ribonucleic acid (rRNA) synthesis. 

Effect of Gene Copy Number and RNA Polymerase Loading on Rate of Pre-rRNA Synthesis in Humans... 

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