Ribosomes activity

Nissen P, Hansen J, Ban N et al (2000) The structural basis of ribosome activity in peptide bond synthesis. Science 289 920-930... 

Ribosome activating cytotoxic proteins that irreversibly inhibit protein synthesis in cells, causing cell death. They are obtained from bacteria (Escherichia coli serotype 0157 H7). Verotoxin 1 is almost identical to shiga toxin (C16-A032) and differs only by a single amino acid. Verotoxin 2 has significant differences. 

Nelson RJ, Ziegelhoffer T, Nicolet C, Werner-Washburne M, Craig EA (1992) The translation machinery and 70 kd heat shock protein cooperate in protein synthesis. Cell 71 97-105 Nissen P, Hansen J, Ban N, Moore PB, Steitz TA (2000) The structural basis of ribosome activity in peptide bond synthesis. Science 289 920-930... 

Wimberly BT, Guymon R, McCutcheon JP, White SW, Ramakrishnan V (1999) A detailed view of a ribosomal active site the structure of the LI 1-RNA complex. Cell 97 491-502... 

Nickel Essential trace element Chicks and rats raised on deficient diet show impaired liver function and morphology stabilizes coiled ribosomes. Active metal in several hydrogenases and plant ureases Very toxic to most plants, moderately so to mammals carcinogenic. Local industrial pollutant of air and water. 

Polyribosome (polysome). A complex of an mRNA and two or more ribosomes actively engaged in protein synthesis. 

RIPs are plant protein toxins that are able to inhibit enzymatically ribosomal activity and are therefore highly cytotoxic [98]. RIPs are taken up in the cells by means of endocytosis, and only a small fraction (5% or less) are translocated to the cytosol where the toxins inhibit the protein synthesis and eventually kill the cell. PCI may be used to increase both the efficacy and specificity of these toxins. RIPs are divided into two groups, type I and type II. Type II RIPs, like ricin, consists of two polypeptide chains, one cytotoxic A-chain with /V-glycosidase activity and one B-chain which binds to the cell surface. Type I RIPs, like gelonin, agrostin, and saporin, lack the B chain, which make them poorly transported over the cell- and intracellular membranes to the cell cytosol. Hence, the cytotoxic effect of these protein toxins is usually absent or very low. A considerable cytotoxic effect of type I RIPs has been shown in combination with PCI, both in vitro and in vivo [25, 99]. 

Ricin toxin consists of two protein moieties connected by a disulphide bridge. Chain A (Mw 32 kD) blocks the ribosomal activity, and chain B (Mw 34 kD) is responsible for cell entry of the A chain. 

The answer is e. (Murray, pp 452-467. Scriver, pp 3-45. Sack, pp 1-40. Wilson, pp 101-120.) Puromycin is virtually identical in structure to the 3 -terminal end of tyrosinyl-tRNA. In both eukaryotic and prokaryotic cells, it is accepted as a tyrosinyl-tRNA analogue. As such, it is incorporated into the carboxy-terminal position ol a peptide at the aminoacyl (A) site on ribosomes, causing premature release of the nascent polypeptide. Thus, puromycin inhibits protein synthesis in both human and bacterial cells. Streptomycin, like tetracycline and chloramphenicol, inhibits ribosomal activity. Mitomycin covalently cross-links DNA, which prevents cell replication. Rifampicin is an inhibitor of bacterial DNA-dependent RNA polymerase. 

Apparently independently of its enzymatic activity, CuZnSOD also plays a role in the regulation of 80S-ribosome activity in S. cerevisiae and was identified as a new inhibitor regulating activity of PK60S kinase, forming an inactive complex with the kinase [153,154]. 

Proteins are assembled on ribosomes in a linear sequence specified by the base sequence in an mRNA. If any of the amino acids is not present, the process stops when the base sequence that specifies its incorporation into the protein enters the ribosomal active site. 

Nucleotide metabolism and ribosomal activity during synchronized cell... 

Henshaw EC, Hirsch CA, Morton BE, Hiart BM (1971) Control of protein synthesis in mammalian tissues through changes in ribosome activity. J Biol Chem 246 436-446 Hepher B (1988) Nutrition of pond fishes. Cambridge Univ Press, Camridge... 

The structural basis of ribosome activity in peptide bond synthesis. SCIENCE 289 920—930 (2000). Reprinted with permission from AAAS. Also reprinted from Monro, R. E., and Marker, K A, Ribosome-catalysed reaction of puromycin with a formylmethio-nine containing oligonucleotide,/ Mol. Biol. 25 pp. 347—350. Copyright 1967, with permission of Elsevier.)... 

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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