Figure 4. The toggled conformation of the J2/3 junction.

The structure of the OiD1-5 ribozyme solved in the presence of Na⁺/Mg²⁺ at 3.2 Å resolution shows a concerted rotation (gray dotted arrows) of G288 and C377 from the triple helix conformation (semi-transparent sticks, drawn using the coordinates of the K⁺/Mg²⁺ structure) to the toggled conformation (pink solid sticks). The toggled conformation is stabilized by a new network of hydrogen bonds (black dotted lines, distances in angstroms), which involves also a solvent molecule (W) and G321 in domain 3. See also Figure S4.