Ca2+ induces the formation of two distinct subpopulations of group II intron molecules

The folding pathway of the Sc.ai5γ derived group II intron ribozyme D135 is highly specific to the correct M(2+) cofactor. Upon partial replacement of Mg(2+) with Ca(2+), the molecules split into two distinct static subpopulations that are not interchangeable. Type 2 molecules thereby form a compact but misfolded state.