Increased Rates of tRNA Charging Through Modification of the Enzyme-Aminoacyl-Adenylate Complex of Phenylalanyl-tRNA Synthetase

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The transfer of amino acid to tRNA by Escherichia coli phenylalanyl‐tRNA synthetase (PheRS) was studied using replacements of Ala294 in the α subunit previously shown to have modified amino acid specificity. Steady‐state analysis of tRNA charging showed little difference between wild‐type and mutants, whereas pre‐steady‐state analysis revealed higher rates of tRNA charging by both the A294S PheRS‐phenylalanyl adenylate and the A294G PheRS‐p‐Cl‐phenylalanyl adenylate. The decrease in energy required for the formation of the transition state of amino acid transfer in these mutants could be related to a weaker binding of the amino acid in the aminoacyl adenylate complex. Thus a compromise appears to exist between amino acid activation and tRNA charging, because slowing down the first step increases the rate of the second step, possibly as a result of decreased stability of the PheRS·amino acid‐AMP complex.


This article was originally published in FEBS Letters, volume 358, in 1995.


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