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)

Factor requirements for yeast and rat liver ribosomes were determined in several different reactions using either yeast or liver factors. In polymerization assays yeast ribosomes required a factor in addition to elongation factor 1 (EF-1) and elongation factor 2 (EP-2). The third factor (EF-3) requirement was observed with EFs from either yeast or liver for both poly(U)-directed polyphenylalanine synthesis and elongation of endogenous peptidyl-tRNA. No significant effect of EF-3 was observed with liver risomes in either assay. In contrast to results with polypeptide synthesis EF-3 was not required for EF-1 dependent binding of [3H]Phe-tRNA or the translocation-dependent formation of N-acetylphenylalanylpuromycin. Up to 2-fold stimulation of the binding reaction was observed with saturating levels of either yeast or liver EF-1. No effect of EF-3 was observed on ribosome-EF-2-GDP-fusidic acid complex formation. The data suggest that the yeast EF-3 may be a loosely bound ribosomal protein which is not required for a specific step in the elongation cycle but is involved in the coordination of the partial reactions required for polymerization.
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PMID:Dissimilarity in protein chain elongation factor requirements between yeast and rat liver ribosomes. 32 Feb 8

Two protein factors (A and B) have been partially purified from Escherichia coli supernatant which, in combination, are more effective than 0.5 M NH4Cl in stimulating ribosomes for AcPhe-tRNA and fMet-tRNA binding, for the puromycin reaction, and for incorporating acetylphenylalanine from AcPhe-tRNA into polypeptide. The factors appear to differ from the initiation factors, the elongation factor EF-T, and ribosomal proteins. Some uncertainty exists as to whether factor B is different from EF-G. To maximize the effect of the factors in initiator tRNA binding, we preincubated the ribosomes with the factors and carried out the binding assay for a short period at 15 degrees C. Maximal stimulation of binding occurred after about a 2-min preincubation at 37 degrees C. Longer preincubation times were required at 15 degrees C, and only slight stimulation was observed after preincubation at 0 degrees C. The extent of stimulation by the factors was not affected when the NH4Cl concentration was increased from 40 to 500 mM in the preincubation. The presence of both the 30S and 50S ribosomal subunits is required for the enhancement of AcPhe-tRNA binding. Polyphenylalanine synthesis carried out without AcPhe-tRNA is inhibited by the factors. It is suggested that the factors may act by inducing a structural rearrangement of the ribosomes.
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PMID:Stimulation, by two Escherichia coli supernatant proteins, of the initiation of polypeptide synthesis. 32 8

We investigated the ribonucleolytic breakdown of poly(U), poly(A), RNA trascribed from calf thymus DNA with E. coli RNA polymerase, ribosomal RNA, tRNA and mengovirus RNA by an enzyme fraction obrained from a postribosomal supernatant of Ehrlich ascites tumor cells. The single-stranded homopolyribonucleotides are preferentially degraded by the enzyme fraction with the production of ribonucleoside 5'-monophosphates. The RNase activity is completely dependent on the presence of Mg2+ ions and is highest at Mg2+ and K+ concentrations optimal for cell-free protein synthesis. Ribonucleoside 5'-monophosphates, ribonucleoside 2'(3')-monophosphates, ribonucleoside 2'(3'),5'-bisphosphates and transition state analogs consisting of vanadyl sulfate and either ribonucleosides or ribonucleoside 5'-monophosphates in a molar ratio 1:1 inhibit the ribonucleolytic activity of the enzyme fraction. The ribonucleoside 2'(3'),5'-bisphosphates and the transition state analogs are the most effective inhibitors. However, only in the presence of ribonucleoside 2'(3'),5'-bisphosphates a concomitant stimulation by 50 to 60% of poly(U)-directed polyphenylalanine synthesis is observed; all the other RNase inhibitors tested also inhibit polypeptide synthesis. The results of preliminary experiments show that poly(U) and ribonucleoside 2'(3'),5'-bisphosphates are well suited as ligands for affinity chromatography of ribonucleases from Ehrlich ascites tumor cells.
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PMID:Inhibition of ribonucleases by ribonucleotides and transition state analogs in cell-free extracts from Ehrlich ascites tumor cells. 32 84

Many of the 200 or so non-protein amino acids synthesized by higher plants are related structurally to the constituents of common proteins. L-Canavanine, the guanidinooxy structural analogue of L-arginine, is representative of this group. It has provided valuable insight into the biological effects and the mode of action of non-protein amino acids which acts as analogues of the protein amino acids. The arginyl-tRNA synthetases of numerous canavanine-free species charge canavanine, and canavanine is subsequently incorporated into the nascent polypeptide chain. Production of canavanine-containing proteins ultimately can disrupt critical reactions of RNA and DNA metabolism as well as protein synthesis. Canavanine also affects regulatory and catalytic reactions of arginine metabolism, arginine uptake, formation of structural components, and other cellular precesses. In these ways, canavanine alters essential biochemical reactions and becomes a potent antimetabolite of arginine in a wide spectrum of species. These deleterious properties of canavanine render it a highly toxic secondary plant constituent that probably functions as an allelochemic agent that deters the feeding activity of phytophagous insects and other herbivores.
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PMID:The biological effects and mode of action of L-canavanine, a structural analogue of L-arginine. 33 85

A complex between initiation factor IF-2 and fMet-tRNA can be formed under ionic conditions, which are optimal for initiation complex formation. The complex can be retained on cellulose nitrate filters after fixing with glutaraldehyde. The IF-2 - FMet-tRNA complex formation is not influenced by GTP and GDP. Other nucleoside di of triphosphates also have no effect. Evidence is presented that this complex acts as an intermediate in polypeptide chain initiation. The IF-2 - fMet-tRNA complex formation is not influenced by initiation factors IF-1 and IF-3. The binary complex can be bound to the 30-S subunit in the absence of GTP, which indicates that there is no concomittant binding of the IF-2 - fMet-tRNA complex and the nucleotide moiety to the 30-S subunit. The binding of the binary complex is stimulated by GTP. The influence of some inhibitors of initiation on the IF-2 - fMet-tRNA complex formation has been tested. Aurin tricarboxylic acid appeared to be a strong inhibitor, whereas the sulfhydryl reagents N-ethylmaleimide and p-chloromercuribenzoate had no effect.
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PMID:The involvement of a complex between formylmethionyl-tRNA and initiation factor IF-2 in prokaryotic initiation. 33

Initiation of polypeptide synthesis in a cell-free system of Escherichia coli directed by alfalfa mosaic virus RNA 4 was studied by using either fMet-tRNA or Ac-Phe-tRNA as initiator tRNA. Initiation with fMet-tRNA yielded a product that was identical to the authentic viral coat protein except that the NH2-terminal serine was preceded by fMet instead of being acetylated. When Ac-Phe-tRNA was used as initiator, the biosynthetic product was 10-12 amino acid residues longer, the extra amino acids being located at the NH2-terminus. fMet-tRNA and Ac-Phe-tRNA did not compete for ribosomes during initiation of protein synthesis, as became evident from incorporation studies using both initiator tRNAs simultaneously. It is concluded that E. coli ribosomes recognize two sites on the 5' end of alfalfa mosaic virus RNA 4 that are separated by a region of about 30 nucleotides. The results are in complete agreement with the 5'-terminal nucleotide sequence of this RNA [Koper-Zwarthoff, E. C., Lockhard, R. E., RajBhandary, U. L., Alzner-deWeerd, B. & Bol, J. F. (1977) Proc. Natl. Acad. Sci. USA 74, 5504-5508].
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PMID:Initiation of polypeptide synthesis with various NH2-blocked aminoacyl-tRNAs under the direction of alfalfa mosaic virus RNA 4. 34 Nov 61

The specificity of the cell-free system of Escherichia coli for mRNA was examined, and the "accessibility" of some natural and synthetic RNAs to the ribosomes was determined by measurement of AcPhe-tRNA and fMet-tRNA binding, AcPhe-puromycin and fMet-puromycin formation, and polypeptide synthesis. The E. coli system effectively initiates the translation of various synthetic RNAs with AcPhe-tRNA or fMet-tRNA under conditions optimal for the translation of viral RNA. Poly(A,G,U) is accessible to the ribosomes according to all of the above criteria. Poly(A,C,G,U), 23 S rRNA, R17 RNA, and MS2 RNA, on the other hand, show limited accessibility when tested for initiator tRNA binding, or for AcPhe-puromycin and fMet-puromycin formation. MS2 and R17 RNA, but not poly(A,C,G,U) and 23 S rRNA, show accessibility when measured by polypeptide synthesis. The results suggest that, except at initiator sites of natural mRNA, an RNA containing about equal amounts of all four bases is inaccessible to E. coli ribosomes for polypeptide synthesis. Rate constants obtained for fMet-tRNA binding with MS2 RNA, poly(A,G,U), and poly(C,G,U) indicate that the ribosomes do not have any special affinity for the viral RNA. Thus, the selection of the initiator site in protein synthesis may be critically determined more by the accessibility of the initiator codon than by ribosomal recognition of the site.
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PMID:On the accessibility and selection of the initiator site of mRNA in protein synthesis. 34 82

The activity of ribonuclease P on precursor tRNA substrates from Escherichia coli can be abolished by pretreatment of this enzyme with micrococcal nuclease or pancreatic ribonuclease A, as well as by proteases and by thermal denaturation. Highly purified RNase P exhibits one prominent RNA and one prominent polypeptide component when examined in polyacrylamide gels containing sodium dodecyl sulfate. The buoyant density in CsCl of RNase P, 1.71 g/ml, is characteristic of a protein-RNA complex. The activity of RNase P is inhibited by various RNA molecules. The presence of a discrete RNA component in RNase P appears to be essential for enzymatic function. A model is described for enzyme-substrate recognition in which this RNA component plays an important role.
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PMID:Ribonuclease P: an enzyme with an essential RNA component. 35 97

A mixture of 30 S and 50 S subunits quantitatively absorbs on a column of Sepharose--4B from the buffer: 0.02 M Tris--HCl, pH 7.5, containing 1.5 M (NH4)2SO4. During elution by reverse gradient of ammonium sulphate (1.5--0.05 M) the subunits are eluted at different salt concentrations. Complete separation of subunits is attained in the absence of Mg2+ ions. The 30 S subunits prepared from 70 S ribosomes according to this procedure are fully active in the codon--dependent binding of a specific aminoacyl--tRNA. After their reassociation with 50 S subunits isolated by zonal centrifugation, the resulting 70 S ribosomes are active in polypeptide synthesis at the same degree as control 70 S ribosomes in which both types of subunits were prepared by zonal centrifugation. The initial 70 S ribosomes for the chromatographic separation into subunits can be obtained by their pelleting from a crude extract with subsequent washing with concentrated solutions of NH4Cl in the ultracentrifuge, or by salt fractionation of the crude extract according to a slightly modified procedure of Kurland.
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PMID:Separation of ribosomal subunits of Escherichia coli by Sepharose chromatography using reverse salt gradient. 36 25

Tiamulin, a water-soluble and highly effective semisynthetic derivative of pleuromutilin leads to the formation of physiologically inactive polypeptide chain initiation complexes which readily decompose and do not enter the phase of peptide chain elongation. Once elongation has begun it continues even in the presence of tiamulin as has been shown by measuring the formation of N-acetylphenylalanine-poly(phenylalanine). The formation of abortive initiation complexes was observed regardless of whether AcPhe-tRNA of fMet-tRNA was used as an initiator or whether artificial messengers or a natural messenger, like R17 bacteriophage RNA, was used. When this drug was acting on whole cells, it led to the disappearance of polysomes. The only structures which could be detected were of the monosome size. Therefore, polysomes seem to elongate the polypeptide chains in whole cells in the presence of this antibiotic, but since effective reinitiation is blocked, the polysome pool of the cell soon becomes depleted.
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PMID:The effects of tiamulin, a semisynthetic pleuromutilin derivative, on bacterial polypeptide chain initiation. 36 25


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