Fig. 6.

Folding kinetics of tertiary contacts within different structural contexts. (A) Construct used to isolate the folding and unfolding of the TL/TLR (TL/TLR_iso). Residues are colored as in Fig.1, and residues that are the same as in P4-P6 are colored orange. (B, Top) Constructs that isolate TL/TLR formation (see SI Appendix, Fig. S2 for TL/TLR_iso sequences). (Bottom) Unfolding (Left) and folding (Right) rate constants for ArichU P4-P6 variant (●) and TL/TLR_iso constructs (A7 linker, □; T14 linker, left triangle; and an extended tetraloop helix, right triangle) across a range of Mg²⁺ concentrations. Published data for TL/TLR_iso are shown (A7 linker, □) (100). Lines are shown to guide the eye (published data for the TL/TLR_iso were taken with 100 mM NaCl instead of 100 mM KCl; see SI Appendix, Tables S1 and S3 for values and condition details). (C) Unfolding versus folding rate constants of P4-P6 variants (closed circles: ArichU, A186U, and J5/5a AllU/Arichu) and TL/TLR_iso constructs (open symbols, as in B, and including a P4-P6 helical context, △) in 5 mM Mg²⁺ (black) or Ba²⁺ (purple). The folding rate constant for J5/5a AllU/ArichU P4-P6 is an upper limit indicated by the left arrow. The folding rate constant for I_MC/MCR→F (★) was calculated as described in the SI Appendix, Supporting Methods, Eq. 3. The average unfolding rates in 5 mM Mg²⁺ or Ba²⁺ are shown as black and purple dashed lines, respectively, and were twofold slower in Ba²⁺ than Mg²⁺. Data are from SI Appendix, Tables S1–S3.