Interactions of Phenylalanyl Transfer Ribonucleic Acid Synthetase of Neurospora crassa with Valyl Transfer Ribonucleic Acid of Escherichia coli

Since Phe-tRNA synthetase of Neurospora crassa reacts with tRNAval of Escherichia coli to produce Phe-tRNAval, the parameters that effect the reverse reaction were examined. Similarly, the interaction of Val-tRNA synthetase (E. coli) with Phe-tRNAval and Val-tRNAval (E. coli) was studied. Phe-tRNA synthetase (N. crassa) can catalyze the deacylation of both Phe-tRNAval (E. coli) and Val-tRNAval (E. coli), although the mechanism of deacylation is different in the two cases since the presence of AMP and PPi is required only for the former. In contrast, Val-tRNA synthetase (E. coli) can deacylate Val-tRNAval but not Phe-tRNAval. Val-tRNA synthetase may actually inhibit the nonenzymatic deacylation of Phe-tRNAval. Unfractionated tRNA (N. crassa) markedly inhibits the aminoacylation of tRNAval (E. coli) catalyzed by Phe-tRNA synthetase (N. crassa). The inhibition appears to result from a competition between tRNA (N. crassa) and tRNAval (E. coli) for binding site (or sites) on Phe-tRNA synthetase.