Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:Q96FX7 (tRNA)
 26,753 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The functional role of the Bacillus stearothermophilus 50S ribosomal protein B-L3 (probably homologous to the Escherichia coli protein L2) was examined by chemical modification. The complex [B-L3-23S RNA] was photooxidized in the presence of rose bengal and the modified protein incorporated by reconstitution into 50S ribosomal subunits containing all other unmodified components. Particles containing photooxidized B-L3 are defective in several functional assays, including (1) poly(U)-directed poly(Phe) synthesis, (2) peptidyltransferase activity, (3) ability to associate with a [30S-poly(U)-Phe-tRNA] complex, and (4) binding of elongation factor G and GTP. The rates of loss of the partial functional activities during photooxidation of B-L3 indicate that at least two independent inactivating events are occurring, a faster one, involving oxidation of one or more histidine residues, affecting peptidyltransferase and subunit association activities and a slower one affecting EF-G binding. Therefore the protein B-L3 has one or more histidine residues which are essential for peptidyltransferase and subunit association, and another residue which is essential for EF-G-GTP binding. B-L3 may be the ribosomal peptidyltransferase protein, or a part of the active site, and may contribute functional groups to the other active sites as well.
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PMID:Evidence of the involvement of a 50S ribosomal protein in several active sites. 0 52

Modeccin inhibits polypeptide-chain elongation catalysed by Artemia salina (brine shrimp) ribosomes by inactivating the 60 S ribosomal subunit. Among the individual steps of elongation, peptide-bond formation, catalysed by 60 S peptidyltransferase, is unaffected by the toxin, whereas the binding of EF 2 (elongation factor 2) to ribosomes is strongly inhibited. Modeccin does not affect the poly(U)-dependent non-enzymic binding of either deacylated tRNAPhe or phenylalanyl-tRNA to ribosomes. The inhibitory effect of modeccin on the EF 1 (elongation factor 1)-dependent binding of phenylalanyl-tRNA is discussed, since it is decreased by tRNAPhe, which stimulates the binding reaction. The analysis of the distribution of ribosome-bound radioactivity during protein synthesis shows that modeccin consistently inhibits the radioactivity bound as long-chain peptides, but depending on the experimental conditions, can leave unchanged or even greatly stimulates the radioactivity bound as phenylalanyl-tRNA and/or short-chain peptides. It is concluded that, during the complete elongation cycle, modeccin does not affect the binding of the first aminoacyl-tRNA to ribosomes, but inhibits some step in the subsequent repetitive activity of either EF 1 or EF 2. The results obtained indicate that the mechanism of action of modeccin is very similar to that of ricin and related plant toxins such as abrin and crotin.
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PMID:Effect of modeccin on the steps of peptide-chain elongation. 25 92

During exponential growth, the mutatn strain Escherichia coli 15-28 accumulates 47S particles, which are unusual precursors to 50S ribosomal subunits. The 47S particles have little ability to bind chloramphenicol, but binding of a fragment of aminoacyl-tRNA is about half that by completed subunits. The 70S (and 50S) ribosomes of strain 15-28 and its parent (strain 15TP) do not differ in chloramphenicol binding. Although ribosomes from the mutant are less able than those from the parent to bind the fragment, this difference is not as marked as was found previously [Sims & Wild (1976) Biochem. J. 160, 721-726] for the binding of an analogue of peptidyl-tRNA and for peptidyltransferase activity. The altered activities may arise because strain 15-28 misassembles 50S subunits of altered conformation and because the few proteins that 47S patricles lack have vital functions in some of the partial reactions of protein synthesis.
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PMID:Binding of chloramphenicol and a fragment of aminoacyl-transfer ribonucleic acid to ribosomes and a ribosome precursor from a mutant of Escherichia coli. 35 51

It has been shown that 50S subunits of E. coli MRE-600 ribosomes catalyze the reaction of N-(formyl)-methionyl ester of adenosine 5'-phosphate acting as peptide donor, with Phe-tRNA or CACCA-Phe serving as a peptide acceptor. The reaction is stimulated by cytidine 5'phosphate and inhibited by lincomycin, puromycin and chloramphenicol. The obtained results show that the structure of the donor site of peptidyltransferase is completely assembled on the 50S subunit and 30S subunit is not required for its formation.
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PMID:[Fragment reaction catalyzed by E. coli ribosomes]. 37 8

The chemical syntheses of 6-azido-2'(3')-O-L-phenylalanylpurine ribonucleoside (4a), 2'(3')-O-(4-azido-L-phenylalanyl)adenosine (4b), and cytidylyl(3' leads to 5')-6-azido-2'(3')-O-L-phenylalanylpurine ribonucleoside (7) are described. 6-Azidopurine ribonucleoside 5'-triphosphate (10) was also synthesized starting from 6-methylmercaptopurine ribonucleoside. All of these compounds (4a, 4b, 7, and 10) are readily photolyzed by ultraviolet (UV) light. Compounds 4a, 4b, and 7 are active in the ribosomal peptidyltransferase-catalyzed release of the Ac-Phe residue from the Ac-Phe-tRNA-70S ribosome-poly(U) complex. It follows that the 6-azidopurine moiety of compounds 4a and 7, as well as the 4-azido-L-phenylalanine moiety of 4b, are recognized by the peptidyltransferase enzyme, and therefore these moieties are suggested for incorporation into tRNA as photoaffinity labeling reagents.
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PMID:Design of new photoaffinity labels for ribosomal peptidyltransferase. 61 51

The 70S ribosomes can select the proper initiator tRNA between Met-tRNAfMet and fMet-tRNAfMet. Experiments on binding and on formation of aminoacylpuromycin, as a function of magnesium, potassium, or initiation factors, suggest a two-state equilibrium for 70S particles, involving a minor, active conformation and a major one which is not readily active. The formyl group would act as a specific trigger to select the active conformation. Experimental results are interpreted following this simple model and equilibrium parameters, together with kinetic constants of the peptidyltransferase activity, are presented.
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PMID:Toward an understanding of the formylation of initiator tRNA methionine in prokaryotic protein synthesis. II. A two-state model for the 70S ribosome. 76 22

2'(3')-O-L-Phenylalanylderivatives of fluorescent 1,N6-ethenoadenosine and 3,N4-ethenocytidine were prepared by chemical synthesis. Both compounds are good acceptor substrates in ribosomal peptidyltransferase reactions. Since these compounds cannot form Watson-Crick base pairs, the results indicate that the terminal aminoacyladenosine unit of AA-tRNA is bound to ribosomal protein on the acceptor site of peptidyltransferase and not to rRNA.
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PMID:Fluorescent 2'(3')-O-aminoacylnucleosides-acceptor substrates for ribosomal peptidyltransferase+. 78 23

Total reconstitution experiments performed under various conditions revealed that 5S RNA plays an important role during the last assembly step in vitro leading to an active 50S particle. For the preceding steps this RNA species is dispensable. However, 50S RNA can be integrated efficiently during any of the assembly steps in vitro. The 47S particle, reconstituted in two steps and lacking 5S RNA, shows low but significant activity in many functional tests. High activity could be obtained by incubating this particle with 5S RNA alone, demonstrating the importance of the 5S RNA in generating an active ribosomal conformation. In particular, the activity of the peptidyltransferase (peptidyl-tRNA:aminoacyl-tRNA N-peptidyltransferase; EC 2.3.2.12) center is drastically influenced by 5S RNA. No significant factor-dependent tRNA binding to the A-site was observed with the 47S particle, in contrast to the corresponding P-site binding. The elongation factor G dependent GTPase activity was not affected by the lack of 5S RNA.
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PMID:Role of 5S RNA in assembly and function of the 50S subunit from Escherichia coli. 78 71

50 S subunits of E. coli ribosomes catalyze the reaction of the 2'(3')-N-(formyl) methionine ester of adenosine 5'-phosphate and Phe-tRNA resulting in peptide bond synthesis. Cytidine 5'-phosphate stimulates this process on 50 S ribosomal subunits as well as on intact ribosomes. The obtained data show that the areas of the peptidyltransferase donor site which binds the 3'-terminal fragment of peptidyl-tRNA possess completely formed structures on 50 S ribosomal subunits.
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PMID:Catalysis of the peptide bond formation by 50 S subunits of E. coli ribosomes with N-(formyl) methionine ester of adenylic acid as peptide donor. 79 86

The mechanism of 5'-cytidilic acid stimulation of the reaction between 2'(3')-O-formylmethionine ester of 5'-adenylic acid and phenylalanyl-tRNA catalyzed by E. coli ribosomes has been studied. It has been shown that cytidilic acid binds to the donor site of the peptidyltransferase in the area which is usually occupied by the second nucleotide residue of the peptidyl-tRNA 3'-end. After the binding cytidilic acid stimulates effectively the donor activity of formylmethionine ester of adenylic acid. A number of compounds have been tested as possible stimulants. Both the chemical nature of stimulant and its conformation are important for the stimulating action. A hypothetic scheme is suggested explaining possible causative factors of peptidyl-tRNA translocation from the acceptor site to the donor site after peptide bond formation.
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PMID:[Donor site of E. coli ribosomal peptidyltransferase]. 80 87


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