Valine specific transfer RNA (tRNAVa1) was isolated from Bacillus stearothermophilus and Escherichia wli by chromatography on benzoylated DEAEcellulose (BD-cellulose).
Likewise isoleucine specific transfer RNA (tRNAI1e) was isolated from B. stearothermophilus and from Mywplasma sp. Kid. The thermal denaturation profiles (melting curves) of the two tRNAVa' species in the presence of Mg++ were nearly identical.
However, the T, for the Kid tRNAIIe was about 10°C lower than that for the B . stearothemnophilus tRNA*le. A nuclease and tRNA-free aminoacyl-tRNA synthetase (AA-tRNA synthetase) preparation from B. stearothermophilus was able to function efficiently a t temperatures up to 80°C in the aminoacylation of all four tRNA species. Determination of the amino acid-acceptor activity of each tRNA species as a function of temperature of the aminoacylation reaction showed in each case a strong correlation between the loss of acceptor activity and the thermal denaturation profile of the tRNA. Evidence is presented that the loss in acceptor activity is most likely due to a change in structure of the tRNA as opposed to denaturation of the enzyme. These results further support the idea that correct secondary and/or tertiary structure must be maintained for tRNA to be activc: as a substrate for the AA-tRNA synthetase.