Ribosome, structure

It may be that we should be more concerned with why the bacterial machinery is relatively so simple. In rapidly growing bacterial cells a very substantial fraction of the total cellular protein is involved directly in protein biosynthesis (activating enzymes, ribosomal structural proteins, elongation factors etc). Evolutionary pressure to attain high growth rates may therefore have resulted in a streamlining of the bacterial protein synthesis mechanism to the bare minimum of components, in which case we should not look for some subtlety of regulation in every additional feature of complexity in the eukaryotic system. 

The gap in our understanding of eukaryotic as opposed to prokaryotic systems is most acute in respect of what is known about the stmcture of ribosomes. Nevertheless some progress has been made in the last few years, and several of the approximately 40 different proteins of the large ribosomal subunit and the JO different proteins of the small subunit have now been purified. 

One can anticipate further advances along the same lines as have been exploited in the study of bacterial ribosomes characterisation and amino acid sequencing of the purified proteins, precise determination of their stoichiometry, and investigations into the topography of the ribosomes using methods for the chemical 

Mammalian ribosomes are subject to phosphorylation and probably also to acetylation (5) It is naturally tempting to assume that such modifications affect the activity of the ribosomes in some way. Before this idea can be evaluated it is important to be sure that the phosphorylation observed vitro does in fact occur ijn vivo, and in this respect the history of the study of ribosome 

Ribosomes phosphorylated vitro show no alteration in their translational activity (5, ) Trivial explanations such as the possibility that the ribosomes are dephosphorylated in the translation assay seem to have been eliminated. It is, of course, possible that current assay methods are inadequate to detect subtle changes caused by phosphorylation, but it is equally valid to draw the strai tforward conclusion that phosphorylation does not affect the activity of ribosomes. This is in accord with the fact that changes in the phosphorylation state of ribosomes vivo do not appear to correlate with alterations in the efficiency of the ribosomes in protein biosynthesis. The one possible exception is the phosphorylation of one of the small ribosomal subunit proteins (S2) that occurs after infection by vaccinia virus (8). The timing of the phosphorylation of S2 seems however to be related neither to the shut-off of host cell protein synthesis nor to the switch from early viral protein synthesis to late gene expression, and it remains to be proven whether the phosphorylation has any material effect on ribosome activity or specificity. 

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McMullin, T.W. Hallberg, R.L. (1986). Effect of heat shock on ribosome structure Appearance of a new ribosome associated protein. Mol. Cell. Biol. 6,2527-2535. 

Spirin AS. Ribosomes Structure and Protein Biosynthesis, Benjamin Cummings, Menlo Park, CA, 1986. 

Though solution scattering and electron microscopy can provide information on the shape and size of the ribosome and its subunits, diffraction techniques, such as X-ray analysis, are expected to yield an insight into the ribosomal structure at a much higher resolution. 

Of great interest is the fact that ribosomal subunits and ribosomes themselves have now been crystallized, and low-resolution structural maps have already been obtained. However, to grow suitable crystals and to resolve the ribosomal structure at a sufficiently high resolution remains a great challenge and task to biochemists and crystallographers. 

Isono, K. (1980). In Ribosomes Structure, Function, and Genetics" (G. Chambliss, G. R. Craven, J. Davies, K. Davis, L. Kahan, and M. Nomura, eds.), p. 641. Univ. Park Press, Baltimore, Maryland. 

The ribosome is a unique cellular machine in that its main functional component is RNA whereas proteins seem to play only a structural role. For a long time, it has been debated whether RNA or proteins contribute most to the ribosome s function. With the determination of high-resolution crystal structures, this question could finally be answered. Clearly, these structures have revolutionized the field of ribosome studies. Already in the 1980s, Yonath and coworkers had grown crystals of active ribosomes that diffracted to about 0.6 nm (6 A) (1 A = 0.1nm) resolution. However, owing to the large size of the ribosome of about 2 500 000 Da (lDa=lgmoP), the ribosome structure was not solved to atomic resolution until tbe year 2000. 

Translation. Mature mRNA enters the cytoplasm, where it binds to ribosomes, which convert the RNA information into a peptide sequence. The ribosomes (see p. 250) consist of more than 100 proteins and several RNA molecules (rRNA see p. 82). rRNA plays a role as a ribosomal structural element and is also involved in the binding of mRNA to the ribosome and the formation of the peptide bond. 

Ogle, J. M. Carter, A. P. Ramakrishnan, V. Insights into the decoding mechanism from recent ribosome structures. Trends. Biochem. Sci. 2003, 28, 259-266. 

Garret RA, Douthwaite SR, Liljas A, et al.. The ribosome Structure, function, antibiotics, and cellular interactions, ASM Press, Washington, D.C, 2000. 

Ribosomes—Structures inside a cell where proteins are manufactured. 

Chambliss, G., Craven, G. R., Davies, J., Davies, K., Kahan, L., Nomura, M, (eds) Ribosomes Structure, Function, and Genetics. Baltimore, Univers. Park Press 1980... 

Ogle JM, Brodersen DE, Clemons Jr WM, Tarry MJ, Carter AP, Ramakrishnan V (2001) Recognition of cognate transfer RNA by the 30S ribosomal subunit. Science 292 897-902 Ogle JM, Murphy FV, Tarry MJ, Ramakrishnan V (2002) Selection of tRNA by the ribosome requires a transition from an open to a closed form. Cell 111 721-732 Ogle JM, Carter AP, Ramakrishnan V (2003) Insights into the decoding mechanism from recent ribosome structures. Trends Biochem Sci 28 259-266... 

Puglisi JD, Blanchard KD, Dahlquist RGE, Eason RG, Fourmy D, Lynch SR, Recht Ml, Yoshizawa S (2000) Aminoglycoside antibiotics and decoding. In Garrett RA, Douthwaite SR, Liljas A, Matheson PB, Moore PB, Noller HF (eds) The ribosome structure, function, antibiotics, and cellular interactions. ASM, Washington D.C., 419 29... 

Spirin, A. ((1986)). Ribosome Structure and Protein Synthesis. Benjamin Cummings Publishing. 

The ribosome is a huge complex of protein and nucleic acid that catalyzes protein synthesis. There are differences between prokaryotic and eukaryotic ribosomal structure ... 

Ramakrishnan, V. (2002) Ribosome structure and the mechanism of translation. Cell 108, 557-572. 

Like most trace elements, nickel can activate various enzymes in vitro, but no enzyme has been shown to require nickel, specifically, to be activated. Howevei, mease has been shown to be a nickel metalloenzyme and has been found to contain 6 to 8 atoms of nickel per mole of enzyme (Fishbein et al.. 1976). RNA (ribonucleic add) preparations from diverse sources consistently contain nickel in concentrations many times higher than those found in native materials from which the RNA ts isolated (Wacker-Vallee, 1959 Sunderman, 1965). Nickel may serve to stabilize the ordered structure of RNA. Nickel may have a role in maintaining ribosomal structure (Tal, 1968, 1969). These studies and other information have led to the suggestion that nickel may play a role in nucleic acid and/or protein metabolism. 

Kurland, C. G. Aspects of ribosome structure and function, in Molecular Mechanisms of Protein Biosynthesis (eds.) Weissbach, H., Pestka, S., p. 81, New York, Academic Press 1977... 

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