Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.48 (transcriptase)
9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The reactivity of the sulfhydryl groups of histidyl-t RNA synthetase from Salmonella typhimurium and the effect of substrates on the reactivity has been studied using p-hydroxymercuribenzoate and 5, 5'-dithiobis (2-nitrobenzoic acid) as reagents. It has been found that 5, 5'-dithiobis (2-nitrobenzoic acid) titrates only two sulfhydryl groups per molcule of enzyme and the reaction is essenaitlly monophasic, while p-hydroxymercuribenzoate titrates four sulhydryl groups. As observed kinetically the reaction with p-hydroxymercuribenzoate is strongly biphasic, each phase corresponding to about two sulfhydryl groups per enzyme molecule. With both reagents no detectable difference in sulfhydryl group reactivity was observed when ATP, histidine and tRNA specific for histidine were added individually or in combination to the enzyme. The enzyme activity slowly changes after two or four sulhydryl groups are blocked by 5, 5'-dithiobis (2-nitrobenzoic acid) or p-hydroxymercuribenzoate respectively. A new, stable level of activity is reached that is characterized by a different Km value for the aminoacylation reaction. The results indicate that the sulfhydryl groups reacting with the two reagents used here are neither directly involved in the binding of the substrates nor in the catalytic process. The ultimate change in enzyme activity after reaction of the sulfhydryl groups suggests a transition to an alternative enzyme structure.
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PMID:Histidyl-transfer-ribonucleic-acid synthetase from Salmonella typhimurium. Studies of the sulfhydryl groups. 77 25

Computer-assisted comparisons of the large proteins involved in the replication of viral RNA have revealed a novel domain located near the N termini of these proteins and conserved throughout the so-called 'Sindbis-like' supergroup of positive-strand RNA viruses. This domain encompasses four distinct conserved motifs, with motifs I, II and IV containing an invariant His residue, the AspXXArg signature and an invariant Tyr residue, respectively. Each of the two large groups of viruses within this supergroup, the 'altovirus' group (alphaviruses, tobamoviruses, tobraviruses, hordeiviruses, tricornaviruses, furoviruses, hepatitis E virus and probably rubiviruses), and the 'typovirus' group (tymoviruses, potexviruses, carlaviruses and apple chlorotic leaf spot virus), can be characterized by additional conserved sequence motifs. Based on the available results of biochemical studies and site-directed mutagenesis of the alphavirus proteins, it is hypothesized that this domain may be involved in methylation of the cap during viral RNA maturation. Unlike the other conserved domains, the RNA-dependent RNA polymerase and the RNA helicase, the motifs typical of the putative methyltransferase domain are universal within the Sindbis-like supergroup but are not found in the proteins of any other viruses, constituting a distinctive hallmark of this supergroup.
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PMID:Conservation of the putative methyltransferase domain: a hallmark of the 'Sindbis-like' supergroup of positive-strand RNA viruses. 164 51

We have modified an Escherichia coli vector expressing 66-kDa HIV-1 reverse transcriptase (p66) so that it simultaneously expresses this and the pol-coded protease. The twin expression cassette yields high quantities of both reverse transcriptase and protease; however, under these conditions, 50% of the over-expressed p66 reverse transcriptase is processed, resulting in accumulation of large quantities of p66/p51 enzyme. Furthermore, addition of a poly(histidine) affinity label at the amino terminus of the reverse-transcriptase-coding sequence (His-p66) permits a simple, rapid purification of milligram quantities of either p66 or p66/p51 enzyme from a crude lysate by metal chelate affinity chromatography. Purified His-p66 and His-p66/His-p51 reverse transcriptase exhibit both reverse transcriptase and RNase H activity. Purification by metal chelate chromatography of a p66/p51 enzyme wherein only the p66 component is labelled strengthens the argument for the existence of a heterodimer.
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PMID:Rapid purification of homodimer and heterodimer HIV-1 reverse transcriptase by metal chelate affinity chromatography. 168 98

Jo-1 syndrome is a disease recently described, included on the list of connective tissue diseases. Its clinical features are myositis and/or pulmonary fibrosis associated to the presence of precipitant antibodies against intracellular enzyme call histidine T-RNA synthetase. This antibody is related to pulmonary fibrosis associated to myositis and some scientist gave predictive value on the onset of pulmonary fibrosis in patients with myositis. However, isolated association of pulmonary fibrosis have been exceptionally described. A patient with severe interstitial pulmonary affliction and positive Jo-1 antibody without myositis is presented. The actual knowledge of the disease and its association is reviewed.
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PMID:[Pulmonary fibrosis as a presentation form of the Jo-1 syndrome]. 176 50

The rules of the genetic code are determined by the specific aminoacylation of transfer RNAs by aminoacyl transfer RNA synthetase. A straightforward analysis shows that a system of synthetase-tRNA interactions that relies on anticodons for specificity could, in principle, enable most synthetases to distinguish their cognate tRNA isoacceptors from all others. Although the anticodons of some tRNAs are recognition sites for the cognate aminoacyl tRNA synthetases, for other synthetases the anticodon is dispensable for specific aminoacylation. In particular, alanine and histidine tRNA synthetases aminoacylate small RNA minihelices that reconstruct the part of their cognate tRNAs that is proximate to the amino acid attachment site. Helices with as few as six base pairs can be efficiently aminoacylated. The specificity of aminoacylation is determined by a few nucleotides and can be converted from one amino acid to another by the change of only a few nucleotides. These findings suggest that, for a subgroup of the synthetases, there is a distinct code in the acceptor helix of transfer RNAs that determines aminoacylation specificity.
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PMID:RNA minihelices and the decoding of genetic information. 202 14

Sequences within the conserved, aminoacylatable 3' noncoding regions of brome mosaic virus (BMV) genomic RNAs 1, 2, and 3 direct initiation of negative-strand synthesis by BMV polymerase extracts and, like sequences at the structurally divergent but aminoacylatable 3' end of tobacco mosaic virus (TMV) RNA, are required in cis for RNA replication in vivo. A series of chimeric RNAs in which selected 3' segments were exchanged between the tyrosine-accepting BMV and histidine-accepting TMV RNAs were constructed and their amplification was examined in protoplasts inoculated with or without other BMV and TMV RNAs. TMV derivatives whose 3' noncoding region was replaced by sequences from BMV RNA3 were independently replication competent when the genes for the TMV 130,000-M(r) and 180,000-M(r) replication factors remained intact. TMV replicase can thus utilize the BMV-derived 3' end, though at lower efficiency than the wild-type (wt) TMV 3' end. Providing functional BMV RNA replicase by coinoculation with BMV genomic RNAs 1 and 2 did not improve the amplification of these hybrid genomic RNAs. By contrast, BMV RNA3 derivatives carrying the 3' noncoding region of TMV were not amplified when coinoculated with wt BMV RNA1 and RNA2, wt TMV RNA, or all three. Thus, BMV replicase appeared to be unable to utilize the TMV 3' end, and there was no evidence of intervirus complementation in the replication of any of the hybrid RNAs. In protoplasts coinoculated with BMV RNA1 and RNA2, the nonamplifiable RNA3 derivatives bearing TMV 3' sequences gave rise to diverse new rearranged or recombined RNA species that were amplifiable.
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PMID:Biological activities of hybrid RNAs generated by 3'-end exchanges between tobacco mosaic and brome mosaic viruses. 204 Oct 76

A region of the feline calicivirus (FCV) genome was sequenced which encodes polypeptides that are similar by amino acid alignment analysis to several picornavirus polypeptides. These polypeptides include the 2C polypeptide, the 3C cysteine protease and the 3D RNA-dependent RNA polymerase. The 2C-like region of the FCV genome encodes a GxxGxGKT nucleotide binding motif as well as amino acids which have been shown to be conserved in the picornavirus 2C polypeptides. The FCV RNA-dependent RNA polymerase also shows regions of similarity with picornavirus RNA polymerase sequences including the GDD sequence which is thought to be in or near the active site of the polymerase. The FCV cysteine protease-like sequences have the lowest degree of similarity with picornavirus cysteine proteases of the three regions aligned. However, the cysteine and histidine residues thought to be in the active site of the protease are present and are surrounded by amino acids conserved in the picornavirus cysteine proteases. The order of the polypeptides encoded in the FCV genome is the same as in the picornaviruses with the RNA-dependent RNA polymerase being located at the C-terminus of the FCV polyprotein. However, there is an approximately 40,000 dalton region between the FCV 2C- and the cysteine protease-like polypeptides which has no similarity to any known picornavirus protein. A striking difference between the organization of these sequences in FCV and the picornaviruses is that in the FCV genome, these non-structural polypeptides are encoded near the 5' end of the genomic RNA. Termination of the reading frame encoding these polypeptides occurs approximately 2400 bases from the 3' end of the genomic RNA as compared to 71 bases in the poliovirus genomic RNA.
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PMID:Nucleotide sequence of a region of the feline calicivirus genome which encodes picornavirus-like RNA-dependent RNA polymerase, cysteine protease and 2C polypeptides. 207 82

An 8-kilobase HindIII fragment carrying the histidase gene (hutH) and its regulatory region (hutP), from the Bacillus subtilis histidine utilization (hut) operon, was cloned in the temperate bacteriophage phi 105. Histidine utilization was restored in a hutH1 mutant by the specialized transducing phage (phi 105hutH11). The histidase gene in phi 105hutH11 was inducible and was shown to be under catabolite repression. The nucleotide sequence of 3,932 base pairs including the hutH and hutP loci revealed three open reading frames (ORFs). The molecular weights of ORF1 and ORF2 proteins were calculated to be 16,576 (151 amino acid residues) and 55,675 (508 amino acid residues), respectively. Reverse transcriptase mapping experiments showed that the putative promoter for the hut operon could be recognized by RNA polymerase sigma 43. The transcript starts at an adenosine residue 32 base pairs upstream from the initiation codon of ORF1. hutH+-transforming activity was found in ORF2, indicating that ORF2 encoded the histidase. A hutP1 mutation was determined as a substitution of an amino acid in ORF1. By using a specialized transducing phage containing the wild-type ORF1 gene, it was demonstrated that the presence of ORF1 protein in trans was absolutely required for the induction of the hut operon in a hutP1 mutant. These data strongly suggested that ORF1 encodes a positive regulator of the hut operon.
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PMID:Cloning and nucleotide sequences of histidase and regulatory genes in the Bacillus subtilis hut operon and positive regulation of the operon. 245 13

One surprising outcome of applying the techniques of protein engineering to the enzyme tyrosyl-transfer RNA synthetase was that the enzyme's activity could actually be increased by a specific sequence change. In particular, altering residue threonine 51 to a proline (mutant TP51) increased the enzyme's affinity for tyrosyl adenylate complexes. The non-additive effect of combining the TP51 mutation with a second sequence alteration (histidine 48 to a glycine) suggested that the effect of the TP51 change might be mediated by a structural change involving the peptide backbone. To address the question of the mechanism by which the TP51 change increases the activity of tyrosyl-tRNA synthetase we have determined the structure of the mutant enzyme. We find the change has a purely local effect on the structure of the enzyme, and conclude that the increased activity of the TP51 mutant probably results from the replacement of the polar threonine residue by a non-polar group: in the wild-type enzyme substrate binding is disfavoured by the displacement of solvent from the vicinity of threonine 51. This unfavourable effect is absent in the TP51 mutant.
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PMID:Structure of a mutant of tyrosyl-tRNA synthetase with enhanced catalytic properties. 310 91

1. Aminoacyl-transfer-RNA synthetase activity in extracts prepared from tobacco leaf was increased 3-5-fold when sodium thioglycollate (30mm) and magnesium chloride (16mm) were included in the extraction medium. Omitting sucrose (0.45m) from the extraction medium did not alter the activity. 2. Activity was a linear function of enzyme concentration up to 1 disk (30mg. fresh wt.)/ml. and was not affected by dialysis at any concentration. 3. Activity increased about 13-fold above control values when a mixture of 21 amino acids and amides (1mm) was added to the reaction mixture. 4. Under the conditions used in the standard assay for aminoacyl-transfer-RNA synthetase activity K(m) (ATP) was 0.65mm and K(m) (l-amino acids) was 70mum. 5. Activity above the control value was found with all amino acids and amides tested except alanine, arginine, glutamic acid, glutamine and hydroxyproline. Activity was highest with leucine, isoleucine, valine, cysteine and histidine. Total activity with a mixture of 21 amino acids and amides was 20% lower than the total activity of the enzymes assayed separately.
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PMID:The extraction and assay of aminoacyl-transfer-ribonucleic acid synthetases of tobacco leaf. 422 1


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