ULTRAVIOLET INACTIVATION OF AMINO ACID ACCEPTANCE OF TRANSFER RNA

Effects of 253.7-mμ ultraviolet-light irradiation on amino acid-accepting activity of tRNA from Escherichia coli and yeast were studied under various conditions. When irradiated in a solution of low salt content, E. coli tRNA exhibited less ultraviolet sensitivity than brewer's yeast tRNA for most of the amino acid species examined. Some kinds of tRNA from two strains of the same species exhibited different ultraviolet sensitivities, suggesting that tRNA is strain as well as species specific. The ultraviolet sensitivity of tRNA tended to increase with increasing concentration of tRNA. The inactivation cross section was dependent on pH, increasing steeply with decreasing pH below 7. On the formation of a secondary structure of tRNA by the addition of Mg2+, many kinds of tRNA exhibited a much reduced ultraviolet sensitivity compared to that in dilute salt solution, but there was also a species of tRNA which showed little change, suggesting that the secondary structure around the ultraviolet target region may be considerably different for different kinds of tRNA. The inactivation rate of tRNA irradiated in 2H2O coincided exactly with that irradiated in H2O, indicating that photohydration is not the main cause of inactivation. A tRNA sample exhibited different inactivation kinetics depending on whether the enzyme used in the assay was from an homologous or heterologous organism, indicating the potential usefulness of such experiments for studies of species specificity in the tRNA-aminoacyl-RNA synthetase relationship. © 1968.