The REMD simulations recapitulate many of the key features and trends observed based on the melting and NMR data, including the existence of stacking interactions that are weakened by the A29C mutation, the formation of helical geometry that may be kinked in A29C at the mutation site, and an increase in dynamic disorder towards the terminal ends and localized about C29 in the mutant. However, the REMD simulations showed weaker agreement with sugar RDCs or sugar conformation, particularly in the A29C mutant, and had increased dynamics compared to the NMR data. Prior studies on HIV-1 TAR RNA noted higher levels of dynamics in CHARMM simulations compared to NMR measurements (75) . Our studies indicate that suboptimal base stacking energies may be a source of these excess dynamics. However, a quantitative assessment of the simulations requires the application of domain-elongation methods to rigorously decouple internal and overall motions, and make it possible to quantitatively predict NMR measurements (33, (75) (76) (77) . In addition, MD simulations that retain aspects of time are required to compare the rates of dynamics observed by relaxation and exchange broadening type measurements. The simplicity of ssRNA offers a much needed model system for such studies directed at rigorously examining currently used nucleic acid force fields.