Thermodynamic studies of RNA stability.

Enthalpies and entropies of helix stabilization due to addition of 3' terminal unpaired nucleotides to a CCGG or GGCC core double helix are derived from UV melting studies. The results suggest stacking provides a significant fraction of the free energy of a terminal base pair. The effects of temperature, aggregation, and ionic strength on the determination of thermodynamic parameters are considered. Helix propagation parameters are revised and extended based on recent additions to the data set.