Interactions of Phenylalanyl Transfer Ribonucleic Acid Synthetase of Neurospora crassa with Valyl Transfer Ribonucleic Acid of Escherichia co&*

Since Phe-tRNA synthetase of Neurospora crassa reacts with tRNAV”’ of Escherichia coli to produce Phe-tRNAV&‘, the parameters that effect the reverse reaction were examined. Similarly, the interaction of Val-tRNA synthetase (E. coti) with Phe-tRNAVal and Val-tRNAVal (E. coli) was studied. Phe-tRNA synthetase (N. crassa) can catalyze the deacylation of both Phe-tRNAVa 1 (E. coli) and Val-tRNAV”’ (E. coti), 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-tRNA Va 1 but not Phe-tRNAVal. Val-tRNA synthetase may actually inhibit the nonenzymatic deacylation of Phe-tRNAVa l. Unfractionated tRNA (N. crassa) markedly inhibits the aminoacylation of tRNA Val (E. coli) catalyzed by Phe-tRNA synthetase (N. crassa). The inhibition appears to result from a competition between tRNA (iV. crassa) and tRNAV”’ (E. coli) for binding site (or sites) on Phe-tRNA synthetase.