Kinetics of the renaturation of yeast tRNA3 leu.

Yeast tRNA₃^Leu is one of several tRNA molecules which can adopt a stable, biologically inactive, denatured conformation. The circular dichroism of the native and denatured conformers differs, providing the basis for the present study of the mechanism for the renaturation process. Conversion of the denatured structure to the native takes place in two steps: a rapid change occurring immediately on addition of Mg⁺⁺, followed by a slower, strongly temperature-dependent step which returns the molecule to its biologically active state. Optimal kinetic data for the second step could be obtained at 285 nm. Analysis of the time dependence of Δε₂₈₅ by the Guggenheim method demonstrated that this step follows first-order kinetics. The temperature dependence of the rate constants over the range 32–41°C yielded the following parameters for the rate-limiting step: E_a = 69 kcal/mole, ΔH^? = 69 kcal/mole, and ΔS^? = 146 cal/mole deg. Values of this magnitude are typical of order—order transitions in nucleic acids.