Fig. 4: Effects of KL interaction on rCbl folding.

a Major conformations for rCbl M2 and M3 mutants in the absence of ligand. Both mutants exhibit dominant (>80%) Y-shaped particles, and minor (<10% each) P- and candy-shaped particles reminiscent of the non-mutant conformations. b AFM images (top) and recapitulated structures (bottom) for Y1 and Y2 conformers of rCbl, and Y3 and Y4 conformers of M2 and M3 mutants, respectively. P1, P5, and P13 helices are colored in green, purple and blue, respectively. Scale bars of 5 nm are shown in the right bottom corner for (a) and (b). c Population tallies of Y conformers in the rCbl, M2 and M3 samples in the absence or presence of ligand. In all cases, the Y population is unaffected by ligand binding. d Isotherms for rCbl (black), M2 (blue), and M3 (red). The isotherms shown are from experiments performed using freshly prepared samples at 50 µM RNA and 500 µM ligand concentrations and under the same buffer conditions (“Methods”). The raw isotherms for rCbl, M2, and M3 are shown in Supplementary Fig. 4b, c, and d, respectively. Titrations with rCbl and M3 were performed twice. The titration with M2 was performed only once since the deletion of P13 is a more extreme approach to abolishing the KL interaction, whose effect is sufficiently demonstrated in M3, which has only disrupting mutations in L13. Source data are provided as a Source Data file.