valyl-tRNA Synthetase Activity Research Articles

Lack of specificity of isoleucyl-tRNA synthetase: Evidence for anomalous charging of tRNA

1. 1. Partially purified preparations of isoleucyl-tRNA synthetase (EC 6.1.1.5) from Bacillus stearothermophilus devoid of valyl-tRNA synthetase (EC 6.1.1.9) activity when tested at 50–60° acquire above 70° the ability to catalyze the formation of valyl-tRNA. 2. 2. Chromatography on methylated albumin of the valyl-tRNA thus formed, as well as competition experiments performed in the presence of unlabeled isoleucine in excess, and experiments performed using tRNA oxidized with periodate after protection with isoleucine, consistently show that above 70° isoleucyl-tRNA synthetase catalyses the attachment of valine to tRNA specific for isoleucine. Such an anomalous charging of tRNA could produce a coding error. 3. 3. Some possible implications of these results are briefly discussed.