Fig. 4.
PRE complexes bearing matched and mismatched peptidyl-tRNA anticodon/mRNA codon pairs within the A site exhibit marked differences in the rates of late translocation steps. (A) Schematic of the translocation reaction coordinate monitored in S13/L5-labeled PRE complexes, where the sites of donor (S13) and acceptor (L5) fluorophore labeling are indicated with green and red circles, respectively. (B) Population FRET histograms showing pre–steady-state EF-G–catalyzed translocation of S13/L5-labeled PRE complexes bearing peptidyl-tRNALys in the A site programmed with either a cognate (AAA) or near-cognate (AAU, AUA, or UAA) mRNA codon. Data were acquired at a 1-s time resolution. The number (n) of individual FRET trajectories in each histogram is indicated.