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Query: EC:6.1.1.12 (aspartyl-tRNA synthetase)
 233 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Aspartylation of mammalian tRNAAsp by bacteria-expressed human aspartyl-tRNA synthetase (hDRS) was examined. The kinetics of the aspartylation of tRNA was consistent with the following reaction pathway, [formula: see text] where E, represents aspartyl-tRNA synthetase. A set of rate constants was obtained which fit single turnover time courses at varying concentrations of the enzyme, tRNA, and AMP using the SAAM program. The dissociation of Asp-tRNA (k3) was found to be rate limiting. The elongation factor 1 alpha (EF1 alpha) and GTP stimulated the hDRS aspartylation. The stimulation depended on the presence of both EF1 alpha and GTP. Kinetic analysis indicated that EF1 alpha formed a complex with the hDRS-Asp-tRNA complex and stimulated the dissociation of Asp-tRNA. In the presence of 0.5 M NH4Cl, which enhances the binding of Asp-tRNA by EF1 alpha, hDRS-bound Asp-tRNA can be transferred directly to EF1 alpha. The implications of these results on the function of the multi-tRNA synthetase complex will be discussed.
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PMID:Mechanisms of the transfer of aminoacyl-tRNA from aminoacyl-tRNA synthetase to the elongation factor 1 alpha. 780 21

The aspA gene, encoding the aspartyl-tRNA synthetase (AspRS) from the hyperthermophilic archaeon Pyrococcus sp. KOD1, was expressed in Escherichia coli. The KOD1 AspRS, which was purified to homogeneity and was shown to be functional in dimeric form, aminoacylated tRNA from KOD1. The optimum temperature for this activity was 65 degrees C, which was lower than that for the cell growth of KOD1 (85 degrees C). However, it increased to 75 degrees C by the addition of polyamine molecules, such as putrescine, spermine, and spermidine. Analysis of the thermal denaturations of the enzyme and of KOD1-tRNA indicated that neither of them was denatured at temperatures below 70 degrees C. These results suggest polyamine is one of the factors which are required to stabilize the AspRS-tRNA complex in vivo. In order to determine whether the nucleotide triphosphate (NTP) is required for Asp-tRNA synthesis, the aminoacylation was examined in the presence of each of the four NTPs. AspRS most effectively aminoacylated tRNA in the presence of ATP. However, we also found that the enzyme aminoacylated it even in the presence of GTP and UTP as well. Archaeon synthetase may have an interesting system to utilize other NTPs than ATP. The extreme conditions of early life may have given rise to these unique characteristics which then disappeared from developed organisms through evolution.
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PMID:Unusual enzyme characteristics of aspartyl-tRNA synthetase from hyperthermophilic archaeon Pyrococcus sp. KOD1. 892 30

Aminoacyl-tRNA is generally formed by aminoacyl-tRNA synthetases, a family of 20 enzymes essential for accurate protein synthesis. However, most bacteria generate one of the two amide aminoacyl-tRNAs, Asn-tRNA or Gln-tRNA, by transamidation of mischarged Asp-tRNA(Asn) or Glu-tRNA(Gln) catalyzed by a heterotrimeric amidotransferase (encoded by the gatA, gatB, and gatC genes). The Chlamydia trachomatis genome sequence reveals genes for 18 synthetases, whereas those for asparaginyl-tRNA synthetase and glutaminyl-tRNA synthetase are absent. Yet the genome harbors three gat genes in an operon-like arrangement (gatCAB). We reasoned that Chlamydia uses the gatCAB-encoded amidotransferase to generate both Asn-tRNA and Gln-tRNA. C. trachomatis aspartyl-tRNA synthetase and glutamyl-tRNA synthetase were shown to be non-discriminating synthetases that form the misacylated tRNA(Asn) and tRNA(Gln) species. A preparation of pure heterotrimeric recombinant C. trachomatis amidotransferase converted Asp-tRNA(Asn) and Glu-tRNA(Gln) into Asn-tRNA and Gln-tRNA, respectively. The enzyme used glutamine, asparagine, or ammonia as amide donors in the presence of either ATP or GTP. These results suggest that C. trachomatis employs the dual specificity gatCAB-encoded amidotransferase and 18 aminoacyl-tRNA synthetases to create the complete set of 20 aminoacyl-tRNAs.
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PMID:A single amidotransferase forms asparaginyl-tRNA and glutaminyl-tRNA in Chlamydia trachomatis. 1158 42