Figure 8.

Effect of modifications on native state stability and dynamics of bmt tRNA^Leu. (A) Leucylation reactions of the bmt tRNA^Leu_UAA transcript performed at different concentrations of Mg²⁺. The tRNA was preincubated in 2.5 mM ATP, 10 mM Leu, and the indicated concentrations of Mg²⁺ for 30 min before initiating the reaction with the addition of 5 μM LARS2. (B) Leucylation reaction of bmt tRNA^Leu_UAA transcript preincubated either in the absence or presence of 20 mM Mg²⁺, before simultaneously initiating the reaction with 5 μM LARS2 and readjusting the Mg²⁺ concentration to 20 mM Mg²⁺. Rate constants for the slow phases were 1.27 min^–1 (Δ) and 1.42 min^–1 (∇), and the Y-intercepts were 0.53 and 0.86, respectively. The rate constants for the fast phases were too fast to be measured by manual pipetting. (C) Leucylation reactions of modified bmt tRNA^Leu isolated from cells, performed as described for panel A. (D) Plot of the normalized fraction of the native state as a function of Mg²⁺ concentration. The half-maximum Mg²⁺ concentrations for folding to the native state (Mg_1/2) are 0.59 mM for modified tRNA and 2.23 mM for the unmodified transcript tRNA.