The Thermodynamics and Kinetics of Conformational Changes in 5-S RNA from Escherichia coli

Solutions of native, renatured and denatured 5-S RNA from Escherichia coli were each found to revert to a mixture of the denatured and renatured forms when incubated at elevated temperatures in the absence of divalent cations. The equilibrium and rate constants for the renaturation and denaturation reactions were studied as a function of temperature and concentration of added NaCl. The enthalpy and entropy of denaturation and the activation energies were determined. The activation energies for the renaturation reaction were found to be almost independent of the salt concentration, whereas the other parameters increased with the salt concentration. The results are interpreted in terms of a partially unfolded intermediate whose concentration is suppressed by the addition of salt.