Contributions and competition of Mg²⁺ and K⁺ in folding and stabilization of the Twister ribozyme

Adjacent nonbridging phosphate oxygen (NBPO) pairs in contact with K⁺ ions at 0 mM MgCl₂ (black lines) and at 100 mM MgCl₂ (red lines). Shown is the probability of selected NBPO pairs within 9 Å (solid lines) and the probability of K⁺ ions (dashed lines) within 6.5 Å of NBPOs of both phosphates. The color of the text defining the interacting pairs corresponds to the NPBO pairs shown in Figure S3c with the exception of C14—A40 and C15—A17 that are not shown in Supplemental Figure S3c.