Figure 7.

How m⁶A modification affects RF2-dependent termination at near-cognate for RF2 UAG codon. Ribosomal termination complex RT₀ (Figure 1B), at concentration 0.05 μM with native UAG (A) or modified Um⁶AG (B) codon in A site and with ³H-labelled fMet-Phe-Tyr-tRNA^Tyr in P site were reacted with RF2 at indicated concentrations. The fractional extents (y-axis) of terminated ribosomes, RT₃ (Figure 1B), are shown as functions of time (x-axis) Inserts: spontaneous termination without RF2. From these curves average reaction times for peptide release were estimated and their inverses, the generalized rate constants for peptide release, k_rel, are displayed in (C) for UAG and (D) for Um⁶AG. The maximal rates (k_cat) and efficiencies (k_cat/K_m) for these termination reactions are summarized in Table 2.