Figure 2.

Chemical shift mapping of Na⁺ and Mg²⁺ association with TAR RNA. On the left, the secondary structure of the TAR construct used in this study. The wild-type loop is replaced with a UUCG loop. (A) 2D HSQC spectra of TAR recorded in the presence of Na⁺ (25 mM, 160 mM and 320 mM) and Mg²⁺ (25 mM Na⁺/4 mM Mg²⁺). Residues undergoing the largest chemical shift perturbations (top 20% for a given type of resonance) upon Na⁺ and Mg²⁺ binding are highlighted in blue and purple square boxes respectively on the TAR secondary structure. (B) Representative Na⁺ and Mg²⁺ titration curves with K_d values ( in M for Na⁺ and mM for Mg²⁺) shown at the end of each curve.