Abstract
It has previously been shown that tryptophanyl-tRNA synthetase from Bacillus stearothermophilus crystallizes in different forms, depending on the substrates present during crystallization [Carter, C. W., Jr., & Carter, C. W. (1979) J. Biol. Chem. 254, 12219-12223]. Radiolabeling experiments show that the tetragonal crystals (type IV), grown in the presence of tryptophan and ATP, contain enzymatically formed 3'(2')-tryptophanyladenosine 5'-triphosphate (Trp-ATP). Trp-ATP is formed by acyl transfer of the tryptophanyl moiety of an acyladenylate intermediate, Trp-5'-AMP, to a second molecule of ATP bound in the site normally occupied by the 3' CCA terminus of tRNATrp. This compound is therefore a chemical marker in type IV crystals for that part of the tRNA binding site on the synthetase. Solution of this crystal structure, now in progress, may therefore provide useful information concerning the mechanism of aminoacylation of tRNATrp by this enzyme and may help locate its tRNA binding site.
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