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 major form of methionine tRNA operational in the elongation of protein synthesis in mouse myeloma cells was purufied from these cells after they had been cultured in the presence of [32P]-phosphate. This [32P]tRNA4-Met species was then digested with T1 RNase or pancreatic RNase so as to obtain both complete and partial RNase digestion products. The nucleotide sequences of these fragments were analysed to enable the derivation of the complete primary structure of this tRNA. tRNA4-Met of mouse myeloma cells is 76 nucleotides in length and contains 15 modified nucleotides. It is the only tRNA yet sequenced which has been found to possess the minor nucleoside 2-methylguanosine (m2G) within the amino acid (a) stem, and also to have an anticodon (c) stem of only 4 and not 5 base-pairs. The loop IV sequence of eukaryotic initiator methionine tRNA (tRNAf-Met) species, -A-U-C-G-m1A-A-A-, IS NOT FOUND IN TRNA4-Met and is therefore absent from at least one of the methionine tRNAs functioning in polypeptide elongation in mammalian cells. This is consistent with the suggested importance of this loop structure in the initiator function of tRNAf-Met in eukaryotic organisms. Three distinct regions of the tRNA cloverleaf, the (b) stem, the anticodon loop (loop II), and loop III, are substantially conserved in structure between tRNAf-Met and tRNA4-Met of mouse myeloma cells. These regions of the structures of mammalian methionine tRNAs probably do not determine whether a certain tRNA-Met will function in the initiation or elongation of protein synthesis, although they might be important in tRNA-Met recognition if the different cytoplasmic tRNA-Met species of mammalian cells are aminoacylated by a single activating enzyme.
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PMID:The nucleotide sequence of a methionine tRNA which functions in protein elongation in mouse myeloma cells. 116 34

KF (30 mM) strongly inhibits polypeptide chain initiation in the reticulocyte lysate cell-free system.. Chain elongation is partially inhibited but proceeds to a significant extent with little initiation of new chains. Polysome breakdown is incomplete after incubations as long as 20 min. Under these conditions deacylated tRNA-Met accumulates in a fraction sedimenting faster than 120 S and thus may be associated with ribosomes bound to mRNA. Incubation of the system with KF results in the accumulation of a complex which can initiate synthesis of polypeptide chains in the presence of aurintricarboxylate; KF thus inhibits a step in initiation after that inhibited by aurintricarboxylate. The accumulation of deacylated tRNA-Met is correlated with the accumulation of the aurintricarboxylate-resistant complex. Both phenomema are dependent on KF and both are inhibited by aurintricarboxylate in the same range of concentrations which inhibit initiation of protein synthesis.
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PMID:Fluoride inhibition of the initiation of protein synthesis in the reticulocyte lysate cell-free system. 116 96

Elongation factor EF1 was found in a low salt homogenate of wheat embryos, either in the 100 000 X g supernatant or in the ribosome pellet. The ribosome-linked EF1 (EF1R), deteched by high salt washing, was purified to electrophoretical homogenetiy and its molecular and functional properties compared to those of a purified high molecular weight species of EF1 obtained from cytoplasm (EF1H). The two forms are associations of different polypeptides having in common only the polypeptide which can form the ternary complex with aminoacyl-tRNA and GTP. Whereas EF1R is able to fulfill all the EF1 functions, EF1H, incubated with ribosomes completely deprived of elongation factors, can catalyze the aminoacyl-tRNA binding to ribosomes, but, in the presence of EF2, forms only a very small amount of poly(Phe).
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PMID:Subcellular distribution and functional properties of different forms of elongation fractor EF1 from wheat embryos. 118 86

Treatment of rats with the aminonucleoside of puromycin, which increases the incorporation of labelled phenylalanyl-tRNA into polypeptide chains in liver ribosome preparations studied in vitro, did not change the factor-dependent binding of fMet-tRNA f Met to ribosomes nor the peptidyl transferase function of the ribosomes. Peptidyl transferase function, as measured by fMet-tRNA f Met-puromycin formation, was comparable in the free and bound ribosome preparations. Similarly, the factor-dependent binding of fMet-tRNA f Met to ribosomes was the same in free ribosome preparations obtained from rat liver as it was in bound ribosome preparations that had been freed of membranes by puromycin incubation and high salt wash.
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PMID:fMet-tRNA F Met binding and peptidyl transferase function in free and bound ribosomes from normal and puromycin aminonucleoside-treated rats. 119 50

Binding of methionyl-tRNAf to native 40-S ribosomal subunits is thought to be an early stage in the process of polypeptide chain initiation, and [35S]Met-tRNAf - 40-S-subunit complexes can be isolated from Ehrlich ascites tumour cells following a brief incubation with [35S]methionine. To determine whether this step is subject to modulation by physiological conditions, we have estimated the extent of binding of Met-tRNAf to native- 40S ribosomal subunits in Ehrlich cells under nutritional conditions known to affect the rate of protein synthesis in these cells. Deprivation of either an essential amino acid, lysine, or of glucose, results in a substantial reduction in the proportion of native 40-S subunits which have Met-tRNAf associated with them, and refeeding of lysine to cells deprived of this amino acid partially reverses this effect within 10 min. These effects on the concentration of Met-tRNA - 40-S-subunit complexes are paralleled by changes of similar magnitude in the rate of protein synthesis and in polyribosome profiles. Native 40-S subunits can be spearated by equilibrium density gradient analysis on caesium chloride into two species, with buoyant densities approximately 1.40 and 1.49 g X cm-3. In cells deprived of either lysine or glucose, the radioactivity from [35S]methionine is bound exclusively to the particle of buoyant density 1.40 g X cm-3. In well-fed cells, or in starved cells shortly after refeeding, a significant proportion of the label is associated with a region of the CsCl gradient corresponding to a particle of higher density. The results suggest that the binding of Met-tRNAf to native 40-S ribosomal subunits can be greatly affected by physiological conditions which alter the rate of protein synthesis. This is consistent with a regulatory role for this step in the sequence of reactions involved in initiation of translation.
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PMID:Initiation of protein synthesis in Ehrlich ascites tumour cells. Evidence for physiological variation in the association of methionyl-tRNAf with native 40-S ribosomal subunits in vivo. 123 2

Eukaryotic polypeptide elongation factor 1 (EF-1) from pig liver has been resolved into two complementary factors, EF-1alpha and EF-1beta (Iwasaki, K., Mizumoto, K., Tanka, M., and Kaziro, Y. (1973) J. Biochem. (Tokyo) 74, 849). This paper describes the procedures for purification of EF-1beta and some properties of the purified factor. The purification method includes an aqueous two-phase separation technique, a treatment of the crude factor with sodium cholate and two successive column chromatographies on diethyl-aminoethyl-Sephadex A-50. By this method, EF-1beta was purified about 50-fold starting from the material obtained after two-phase separation followed by ammonium sulfate fractionation with a recovery of 20%. The purified EF-1beta appeared homogeneous, having a molecular weight of about 90,000. It consisted of two unequal subunits of the molecular weights of 55,000 and 30,000. It stimulates polymerization of phenylalanine dependent on poly(U) in the presence of both EF-1alpha and EF-2, as well as the EF-1alpha-dependent binding of phenylalanyl-tRNA to ribosomes in the presence of GTP. However, it had no effect on the stoichiometric binding of phenylalanyl-tRNA to ribosomes dependent on EF-1alpha in the presence of guanyl-5'-yl methylenediphosphonate. These results indicate that the function of EF-1beta is to stimulate the recycling of EF-1alpha.
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PMID:Purification and properties of a new polypeptide chain elongation factor, EF-1beta, from pig liver. 125 99

Escherichia coli Phage Qbeta RNA replicase, an RNA-dependent RNA polymerase, is a tetramer composed of one phage-coded polypeptide and three host-supplied polypeptides which are known to function in the biosynthesis of proteins in the uninfected host. Two of these polypeptides, protein synthesis elongation factors EF-Tu and EF-Ts, are required for initiation of transcription by Qbeta replicase with all templates. Using a previously developed reconstitution system we have examined the effects of modification of EF-Tu on reconstituted replicase activity. The poly(G) polymerase activity of the enzyme can be recovered after pretreatment of the EF-Tu-GDP with either L-1-tosylamido-2-phenylethyl chloromethyl ketone or N-ethylmaleimide, both of which inhibit the aminoacyl-tRNA binding activity of EF-Tu. This suggests that the aminoacyl-tRNA binding site of EF-Tu is not required for Qbeta replicase activity. When Qbeta replicase is treated with kirromycin, an antibiotic which modifies EF-Tu activity by an unknown mechamism, the protein synthetic activity of the EF-Tu in the replicase complex is eliminated but the Qbeta RNA replication activity is only slightly affected. Treatment of pure EF-Tu with kirromycin, however, prevents it from functioning in the renaturation of Qbeta replicase. This antibiotic is not effective against the EF-Tu-Ts complex in the reconstitution assay. Kirromycin at the relatively high concentration used here is found to prevent the formation of the EF-Tu-Ts complex. GDP, which binds to EF-Tu and inhibits formation of the complex with EF-Ts, also inhibits renaturation of Qbeta replicase. It is suggested that the EF-Tu-Ts complex, rather than the individual polypeptides, functions in the renaturation of Qbeta replicase and that the kirromycin and GDP act by preventing formation of this complex.
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PMID:Function and structure in ribonucleic acid phage Qbeta ribonucleic acid replicase. Effect of inhibitors of EF-Tu on ribonucleic acid synthesis and renaturation of active enzyme. 126 42

The SSA/Ro and SSB/La antigens are polypeptides which serve as autoantigens in systemic lupus erythematosus and Sjogren's syndrome. The SSA/Ro contains two major isoforms of 60 kD and 52 kD. The former is the main native antigen while the latter is a major autoantigen in its denatured form. The SSB/La is a single phosphorylated protein of 48 kD. Recently a new protein of 46 kD, termed calregulin, was suggested as an additional component of the SSA/Ro antigens. However, extensive investigations failed to confirm its relation to the SSA/Ro system. Based on molecular techniques and cDNA cloning of these antigens, it was demonstrated that the 60 kD protein is capable of binding RNA and DNA molecules, suggesting a regulatory role in transcription for this antigen. The 52 kD polypeptide contains multiple zinc finger motifs and its sequence is homologous to the mouse rptl protein, which is a T-cell regulating peptide. The SSB/La is associated with precursors of 5S RNA and tRNA, implying that it has a role in the synthesis and maturation of RNA polymerase III transcripts. The 60 kD and 52 kD SSA/Ro components may be associated within the cell. The SSA/Ro and SSB/La may also be in complex in some points of the cell cycle.
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PMID:Target antigens of the SSA/Ro and SSB/La system. 128 96

We have identified an activity in rabbit reticulocyte lysate as peptidyl-tRNA hydrolase, based upon its ability to hydrolyze native reticulocyte peptidyl-tRNA, isolated from polyribosomes, and N-acylaminoacyl-tRNA, and its inability to hydrolyze aminoacyl-tRNA, precisely the same substrate specificity previously reported for peptidyl-tRNA hydrolase from bacteria or yeast. The physiological role of the reticulocyte enzyme may be to hydrolyze and recycle peptidyl-tRNA that has dissociated prematurely from elongating ribosomes, as suggested for the bacterial and yeast enzymes, since reticulocyte peptidyl-tRNA hydrolase is completely incapable of hydrolyzing peptidyl-tRNA that is still bound to polyribosomes. We have purified reticulocyte peptidyl-tRNA hydrolase over 5,000-fold from the postribosomal supernatant with a yield of 14%. The purified product shows a 72-kDa band upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis that has co-purified with enzyme activity and comprises about 90% of the total stained protein, strongly suggesting that the 72-kDa protein is the enzyme. Sucrose density gradient analysis indicates an apparent molecular mass for the native enzyme of 65 kDa, implying that it is a single polypeptide chain. The enzyme is almost completely inactive in the absence of a divalent cation: Mg2+ (1-2 mM) promotes activity best, Mn2+ is partly effective, and Ca2+ and spermidine are ineffective. The hydrolase shows a Km of 0.60 microM and Vmax of 7.1 nmol/min/mg with reticulocyte peptidyl-tRNA, a Km of 60 nM and Vmax of 14 nmol/min/mg with Escherichia coli fMet-tRNA(fMet), and a Km of 100 nM and Vmax of 2.2 nmol/min/mg with yeast N-acetyl-Phe-tRNA(Phe). The enzyme has a pH optimum of 7.0-7.25, it is inactivated by heat (60 degrees C for 5 min), and its activity is almost completely inhibited by pretreatment with N-ethylmaleimide or incubation with 20 mM phosphate. The fact that the enzyme hydrolyzes E. coli but not yeast or reticulocyte fMet-tRNA(fMet) may be explained, at least in part, by structural similarities between prokaryotic tRNA(fMet) and eukaryotic elongator tRNA that are not shared by eukaryotic tRNA(fMet).
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PMID:Purification and initial characterization of peptidyl-tRNA hydrolase from rabbit reticulocytes. 130 7

A 3' region of a previously unknown retroviruslike element named ART-CH (avian retrotransposon from chicken genome) was obtained in the course of polymerase chain reaction-mediated cloning of avian leukosis virus long terminal repeats (LTRs) from DNAs of infected chicken cells. About 50 copies of ART-CH are present in the genome of chickens of different breeds. ART-CH is not found in DNA of quails, ducks, turkeys, or several other birds tested. The ART-CH element is about 3 kb in size, including 388 bp LTRs. The major class of ART-CH-specific RNA, also 3 kb in size, is detected in various organs of chickens. An ART-CH polypurine tract, a tRNA(Trp)-binding site, regions around the TATA box and polyadenylation signal, and the beginning of the putative gag gene strongly resemble the corresponding regions of avian leukosis viruses and EAV, the two described classes of chicken retroviruses. An open reading frame capable of encoding a polypeptide with a putative transmembrane domain is located upstream of the right ART-CH LTR. This sequence, as well as the U3 and U5 regions of the ART-CH LTR, has no obvious similarities with the corresponding parts of other known vertebrate retroviruses and retrotransposons. A short sequence upstream of the right LTR of ART-CH is very similar to sequences which flank the 3' ends of the oncogenes v-src, v-myc, v-fps, and v-crk in four different recombinant avian retroviruses and which are absent from the genomes of other studied avian retroviruses. Thus, ART-CH is a new endogenous chicken provirus that may participate in the formation of recombinant oncogenic retroviruses.
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PMID:ART-CH, a new chicken retroviruslike element. 131 Jul 73


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