Effects of Cosolvents on the Folding and Catalytic Activities of the Hammerhead Ribozyme

The RNA cleavage activity of the hammerhead ribozyme has been compared in various mixed aqueous solutions containing cosolvents. Kinetic analysis revealed that the tested cosolvents enhanced the ribozyme activity, particularly at low MgCl2 concentrations. These enhancements, in some cases of more than tenfold, resulted from a reduction in the Mg2+ concentration required for substrate cleavage. An inverse correlation was found between the MgCl2 concentration essential for efficient catalysis and the dielectric constant values. In contrast, FRET measurements showed no substantial influence of cosolvents on the Mg2+-induced structural transitions. The results suggest that the solution environment has various effects on the Mg2+ interactions involved in the catalysis and global folding of the ribozyme.