Mg2+-dependent folding of a large ribozyme without kinetic traps

The folding kinetics of the catalytic domain of Bacillus subtilis ribonucle ase P is analyzed here by fluorescence and catalytic activity. The folding pathway is apparently free of kinetic traps, as indicated by a decrease in folding rates upon the addition of urea. We apply Mg2+ and urea chevron ana lysis to fully describe the folding and unfolding kinetics of this ribozyme . A folding scheme containing two kinetic intermediates completely accounts for the free energy, the Mg2+ Hill coefficient and the surface buried in t he equilibrium transition. At saturating Mg2+ concentrations, folding is li mited by a barrier that is independent of Mg2+ and urea. These results desc ribe the first trap-free folding pathway of a large ribozyme and indicate t hat kinetic traps are not an obligate feature of RNA folding.