Interestingly, many of the residues that experience chemical shift perturbations following the A29 to C29 mutation also exhibit a greater degree of dynamics as assessed by normalized resonance peak intensities in 2D C-H HSQC spectra (Supplementary Figure S6 ) and carbon relaxation data (R 1 and R 2 ) ( Figure 4B and Supplementary Figure S8 ). In particular, severe line broadening consistent with a slow exchange process occurring at micro-to millisecond timescales manifesting as reduced resonance intensities in 2D spectra and higher R 2 values is observed for C29 in the A29C mutant ( Supplementary  Figures S6 and S8 ). This is not observed for A29 in WT. Smaller but significant line broadening is also observed for residues A31, A32 and U34 (Supplementary Figure S8 ). This line broadening across several residues may reflect exchange between stacked and unstacked conformations. Higher intensities as well as reduced S 2 rel values are observed for residues A27 and A28, indicating a greater degree of fast pico-to nanosecond dynamics ( Supplementary Figures S6 and S8) . Note that the high R 2 and weak signal intensity leads to a higher error in the R 2 /R 1 measurements, particularly for C29.