Post-transcriptional modifications modulate conformational dynamics in human U2–U6 snRNA complex

Magnesium stabilizes the low FRET conformation. (A) Typical FRET trajectories of the unmodified U2–U6 complex in 10 mM (top) and 40 mM Mg²⁺ (bottom). (B) FRET histograms of the unmodified U2–U6 complex obtained in 10 mM (top) and 40 mM Mg²⁺ (bottom). Both FRET trajectories and histograms exhibit three FRET states: low FRET (∼0.2, G), mid FRET (∼0.4, I), and high FRET (∼0.6, N). (C) Observed folding rate constants (k₁, k₋₁, k₂, and k₋₂) of the hU2–U6 complex without post-transcriptionally modified bases in 10 mM (red) and 40 mM Mg²⁺ (purple). (D) Effect of Mg²⁺ on the folding energy landscape of the hU2–U6 complex.