Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcriptional activity of plasmids carrying wild-type and mutant trp operons was visualized in cell lysates of Salmonella typhimurium. Plasmid and transcription-unit sizes varied with the size of the cloned operon. Following 3-(3-indolyl)acrylic acid derepression, all operons of a particular type exhibited the same high level of transcriptional activity. An estimated 11-14 transcripts must be initiated each minute to maintain the 190-base-pair spacing of RNA polymerases observed on the promoter-proximal half of the wild-type trp operon. A decline in RNA polymerase density was observed on promoter-distal portions of cloned trp operons, which may be attributable to premature transcription termination accompanying translation inhibition due to indolylacrylic acid's interference with normal tryptophanyl-tRNA synthetase activity.
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PMID:Electron microscopic visualization of trp operon expression in Salmonella typhimurium. 389 22

A single form of tRNA(Trp) exists in the yeast cytoplasm to respond to the unique codon, UGG, which specifies this amino acid. Mutations in the anticodon of the corresponding gene, which generate potential nonsense suppressor tRNAs, have been generated in vitro and tested in vivo for biological activity. The amber (C35U) and opal (C34U) suppressors show strong and weak activities respectively while the ochre suppressor (C34U,C35U) has no detectable biological activity. To understand the basis for these differences, a set of synthetic tRNA(Trp) genes has been constructed to permit in vitro, T7 RNA polymerase synthesis of transcripts corresponding to the normal and mutant tRNAs. Kinetic parameters for aminoacylation of these transcripts by purified, yeast, tryptophanyl-tRNA synthetase have been measured and compared to values observed using the naturally occurring tRNA(Trp) as a substrate. The efficiency of aminoacylation is reduced by 40, 2000, and 30,000 fold by the C35U, C34U, and C34U,C35U mutations respectively. Interestingly, the C35U change affects only tRNA binding while C34U also alters catalytic efficiency. We conclude that both C34 and C35 are major identity elements in the recognition of tRNA(Trp) by its cognate synthetase. These differences in aminoacylation efficiency closely parallel the in vivo suppressor activities of the mutants.
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PMID:Anticodon bases C34 and C35 are major, positive, identity elements in Saccharomyces cerevisiae tRNA(Trp). 825 61

In this study, the varying reactivities of Bacillus subtilis tryptophanyl-tRNA synthetase toward prokaryotic, eukaryotic, and halophile tRNAs were employed to define the potential identity elements on tRNA(Trp). On this basis mutagenesis was performed to obtain, through in vivo heterologous expression in Escherichia coli and in vitro transcription with T7 RNA polymerase, mutant B. subtilis tRNA(Trp) for comparison with the wild-type. These comparisons served to establish G73 and the anticodon as major identity elements, and A1-U72, G5-C68, and A9 as minor identity elements. While the tryptophanyl-tRNA synthetase from B. subtilis and E. coli require G73 to function, replacement of G73 by A73 favors the enzyme from yeast. This change points to the variation of the identity elements for the same amino acid among different organisms. The similarity in these elements between B. subtilis and E. coli tryptophanyl-tRNA synthetase, however, suggests that identity elements on tRNA, like the active centers on enzymes, undergo evolutionary change at slower rates than less essential portions of the macromolecule.
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PMID:Identity elements of tRNA(Trp). Identification and evolutionary conservation. 848 27