Characterization of the Native and Denatured Conformations of tRNASerand tRNAPhefrom Yeast

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Abstract
Previous work on the partial digestion of the native and denatured forms of tRNASerand tRNAPhefrom yeast with T1‐RNAase was extended. Detailed studies with pancreatic and T2‐RNAase and a few experiments with sheep kidney nuclease and acid RNAase from hog spleen revealed characteristically different fragmentation patterns for the native and denatured forms of the tRNAs. Apparently it is mainly the miniloop and dihydrouridine regions which are involved in the conformational changes responsible for denaturation.The rate constants, activation enthalpies, and activation entropies of the renaturation process were calculated from amino acid acceptance data.When the changes in hyperchromicity at 260 nm of the denatured tRNAs were followed as a function of time, a process was detected which in tRNAPheis 5–10 times and in tRNAser10–20 times faster than the renaturation as measured by acceptor activity. The whole net change in absorption, possibly representing the total net change in base stacking, occurs during the fast, process. The activation enthalpies and activation entropies are different for the fast and the over‐all processes.