Increase in fidelity of rat liver Ile-tRNA formation by both spermine and the aminoacyl-tRNA synthetase complex

Abstract

To examine the polyamine effects on the fidelity at the aminoacylation level and the physiological significance of the existence of the aminoacyl-tRNA synthetase complex (ARSC) in animal cells, a single-chain Ile-tRNA synthetase (IRSS) was isolated from the complex by treatment with trypsin. Ile-tRNA formation by IRSS was strongly stimulated by spermine, similar to the results with ARSC. Two misacylations (Val-tRNA Ile and Ile-tRNA i Met formation) by IRSS were measured. The error frequency was higher in Ile-tRNA i Met formation (tRNA misacylation) than in Val-tRNA Ile formation (amino acid misacylation). Spermine did not influence significantly Ile-tRNA i Met formation, but it stimulated Val-tRNA Ile formation by IRSS. Accordingly, spermine decreased the error frequency of tRNA misacylation, but not amino acid misacylation. These results suggest that the conformational changes of individual tRNA by spermine differ from each other, meaning that spermine influences the interaction between individual tRNA and aminoacyl-tRNA synthetase variously. When the aminoacylations of tRNA Ile from rat liver, yeast, and Escherichia coli were compared with ARSC and IRSS, the relative speed of Ile-tRNA formation with tRNA Ile from other species was faster with IRSS than with ARSC. This indicates that ARSC can recognize tRNA Ile from the same species more specifically than IRSS. These results show that both spermine and ARSC are involved in the increase of fidelity of rat liver Ile-tRNA formation.