Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The origin and development of the protein synthesis mechanism is considered in four successive steps. The genetic code is supposed to be controlled by the relative amount (availability) of various amino acids and nucleotides on the one hand, and utility on each amino acid in the polypeptide. on the other hand. Thus, more simple (inutile) and abundant amino acids tended to correspond to codons which were rich in the less frequent base species, G and C. Features of primitive tRNA in the discrimination of amino acid are discussed. Primitive tRNA is proposed to have a discriminator site for amino acid and, separated from it, an anticodon site for interaction with nucleotides. A hypothetical course of subdivision of various nucleic acid species is proposed. In the scheme, mRNA and ribosomal RNA (rRNA) were derived from more primitive insoluble RNA. DNA appeared in the late, not first, step of the development. Several other aspects of evolutionary development of the whole protein synthesis mechanism, e.g., role of the discriminator site on primitive tRNA, modification and subdivision of code catalogue into a more precise specification of amino acids, and possible primordial interactions between tRNA and tRNA-binding sites on insoluble rRNA, are discussed.
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PMID:The origin of the protein synthesis mechanism. 59 95

A new technique was developed for measuring the amount of peptidyl-tRNA in a protein-synthesizing system in vitro. By this technique the course of the puromycin reaction may be followed and the modes of action of various inhibitors of protein synthesis readily determined. We conclude that the polypeptide alpha sarcin inhibits the binding of aminoacyl-tRNA into the ribosomal 'A' site, that sparsomycin inhibits the peptidyl transferase reaction and that cycloheximide may block translocation.
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PMID:The mode of action of alpha sarcin and a novel assay of the puromycin reaction. 62 83

Partially purified polypeptide chain initiation factors were prepared from the 0.5 M KCl wash of rat liver microsomes. Their activities in connection with dimethylnitrosamine (DMNA)-induced inhibition of protein synthesis were studied by use of the following reactions: (1) poly(U)-directed binding of Phe-tRNA to ribosomes, (2) formation of a GTP-dependent ternary initiation complex with Met-tRNAf, (3) binding of Met-tRNAf to 40-S ribosomal subunits, (4) assembly of a Met-tRNAf containing 80-S ribosomal initiation complex and (5) ribosome-dependent GTPase activity. The inhibition of protein synthesis with DMNA was not associated with a loss of factor activity in any of these reactions. In the binding of Met-tRNAf to 40-S subunits there was a noticeable increase, probably related to the stability of the resulting complex. The Met-tRNA deacylase activity was also increased.
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PMID:Activity of partially purified protein chain initiation factors from the livers of dimethylnitrosamine-treated rats. 64 38

To investigate the basis for the depressed protein synthesis in vivo in magnesium deficient spleens, the activities of splenic subcellular fractions in polypeptide synthesis were studied in vitro. Splenic ribosomes from Mg deficient animals were normal structurally and functionally. In contrast, supernatant fractions from the deficient spleens had a reduced ability to incorporate labeled amino acids into protein, both in the presence of endogenous mRNA and in the presence of added polyuridylic acid. The specific defects observed in the Mg deficient supernatants were twofold: There was a modest reduction in the rate of acylation of tRNA and a more marked reduction in the activity of the elongation factors, EF-I and EF-II. The reduction in elongation factor activity was quantitatively sufficient to account for the inhibition of protein synthesis in vivo.
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PMID:Splenic protein synthesis in magnesium deficiency: mechanism of the inhibition. 70 5

The process, by which FAD is attached covalently to the 6-hydroxy-D-nicotine oxidase apoprotein in D-nicotine-induced cells of Arthrobacter oxidans was studied in vitro. [3H]Adenine-labelled FAD prepared biosynthetically in Clostridium kluyveri was incorporated into the 6-hydroxy-D-nicotine oxidase molecule during cell-free translation. FAD rather than FMN or riboflavin was thus shown to be the flavin derivative transferred to the polypeptide chain. After short-term protein synthesis on ribosomes from induced A. oxidans cells in the presence of an Escherichia coli MRE 600 supernatant fraction and [adenine-2-3H]FAD, THE PEPTIDYL-TRNA fraction was separated from completed polypeptides. Labelled FAD was found to be covalently attached to the tRNA-bound polypeptides. Cleavage of the tRNA-peptide bond released labelled polypeptides the largest of which migrated as authentic 6-hydroxy-D-nicotine oxidase during dodecylsulfate/polyacrylamide gel electrophoresis. These results strongly suggest that FAD is incorporated into the nascent polypeptide chains of 6-hydroxy-D-nicotine oxidase during ribosomal translation.
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PMID:FAD is covalently attached to peptidyl-tRNA during cell-free synthesis of 6-hydroxy-D-nicotine oxidase. 73 74

To quantitate the amount of GTP hydrolyzed during polypeptide chain elongation, an in vitro system containing purified endogenous Escherichia coli polysomes has been developed. The polysomes are washed with 1 M NH4Cl to eliminate endogenous GTPase activities and are depleted of subunits and free ribosomes to diminish the uncoupled elongation factor G-dependent GTP hydrolysis. These polysomes, supplemented with elongation factors, aminoacyl-tRNA, and low concentrations of GTP, incorporate amino acids in their nascent peptide chains. After correcting for a background of uncoupled GTP hydrolysis, it has been found that the incorporation of each molecule of amino acid is associated with the hydrolysis of 2 molecules of GTP.
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PMID:Stoichiometry of polypeptide chain elongation. 76 39

The mode and site of action of inhibitors of translation (initiation, elongation and termination of protein synthesis) in eukaryotic systems is reviewed. The isolation and characterization of a factor is described that binds Ac-Phe-tRNA to form a complex made up of binding factors, Ac-Phe-tRNA, and ribosome. The binding of Ac-Phe-tRNA probably occurs at the ribosomal site involved in the binding of the initiator substrate Met-tRNAF. The effect of inhibitors of the intitiation phase of protein synthesis on the nonenzymic Ac-Phe-tRNA binding to ribosomes is investigated. The two sites translocation model for translation in eukaryotic cells is presented and the effects of inhibitors on the various steps of protein synthesis are determined empirically. The site of action of inhibitors of peptide bond formation at the ribosomal peptidyl transferase center is elucidated. The action of inhibitors of translocation is sutdied in model cell-free systems from human cells. In addition, a number of methylxanthines are shown to enhance the elongation phase in polypeptide synthesis by stimulating the enzymic binding of aminoacyl-tRNA. The effect of caffeine, theophylline and its derivatives are shown to be fairly specific and dependent on the ribosome concentration. Aminophylline is shown to have a similar effect but also enhances aminoacyl-tRNA synthetase activity at low Mg++ concentrations, probably displacing the optimal concentration of Mg++ in the reaction. This second effect of aminophylline appears to be due to the ethylenediamine moiety of aminophylline since it is also observed in the presence of different polyamines but not in the presence of caffeine or theophylline.
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PMID:Antibiotics and compounds affecting tanslation by eukaryotic ribosomes. Specific enhancement of aminoacyl-tRNA binding by methylaxnthines. 76 41

Specific in situ cleavage of 16S rRNA of E. coli has been accomplished by in vitro treatment of 70S ribosomes ("tight couples") with the bacteriocin cloacin DF13. The defective ribosomes, which have fully lost their ability to sustain polypeptide synthesis, are still able to form initiation on complexes with MS2 RNA, but the kinetics are altered. This is apparently due to an improper functioning of initiation factor IF-1, for the defective ribosomal couples respond normally to dissociation by IF-3 but the dissociation is not stimulated by IF-1. The initiation complexes formed with defective ribosomes are fully reactive with puromycin. Their ability to bind alanyl-tRNA is reduced by about 50% at all concentrations of elongation factor Tu studied. Cleavage of the 16S rRNA, not the release of the terminal fragment from the ribosome, causes the block of protein synthesis and the aberrations observed during initiation and elongation.
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PMID:Specific in situ cleavage of 16S ribosomal RNA of Escherichia coli interferes with the function of initiation factor IF-1. 76 82

Formation of the 30S-tRNA initiation complex of Escherichia coli with nonformylated initiator tRNA is stimulated by all three initiation factors and is messenger dependent, whereas the complex formation involving the 70S ribosomes is strongly inhibited by initiation factors when the nonformylated species is used. When the 30S-Met-tRNAfMet complex is first formed and the 50S ribosomal subunit added subsequently, there is no significant inhibition by initiation factors and the nonformylated initiator tRNA is puromycin reactive. This leads to the conclusion that the formylation of the methionyl initator tRNA is only obligatory when polypeptide synthesis is initiated by nondissociated 70S ribosomes.
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PMID:Toward an understanding of the formylation of initiator tRNA methionine in prokaryotic protein synthesis. I. In vitro studies of the 30S and 70S ribosomal-tRNA complex. 76 21

Bottromycin A2 inhibited MS2 phage RNA-dependent protein synthesis as well as polyuridylic acid-(poly(U))- or polyadenylic acid (poly(A))-dependent polypeptide synthesis. When the ribosomal complex with N-acetyl-[14C]phenylalanyl-tRNA (N-acetyl-[14C]Phe-tRNA) at the A site was subjected to bottromycin A2, the release of N-acetyl-[14C]Phe-tRNA was observed while no release of N-acetyl-[14C]Phe-tRNA from the donor site was observed, indicating that the action of bottromycin A2 is specific to the A site of ribosomes. Due to bottromycin's capacity to release [14C]Phe-tRNA or N-acetyl-[14C]Phe-tRNA from the ribosomal acceptor site (A site), bottromycin A2 inhibited the nonenzymatic binding of N-acetyl-[14C]Phe-tRNA and elongation factor T (EF-T)-dependent binding if the concentration of EF-Tu-GTP-[14C]Phe-tRNA ternary complex was low. Our data are consistent with the possibility that the inhibition of overall polypeptide synthesis by bottromycin A2 is at least partly due to bottromycin A2's activity to release aminoacyl- or oligopeptidyl-tRNA from ribosomes. Among 10 antibiotics tested, bottromycin A2 and lincomycin released aminoacyl-tRNA from ribosomes.
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PMID:Mode of action of bottromycin A2. Release of aminoacyl- or peptidyl-tRNA from ribosomes. 77 Apr 64


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