Figure 5: Val-tRF inhibits peptide bond formation. (a) Peptidyl transferase reactions catalyzed by H. volcanii 70S ribosomes (left panel) or 50S subunits (right panel) in the absence (-) or presence of 2.7 μM Val-tRF (a 10-fold molar excess) were performed as described in Material and Methods. The scrambled version of the Val-tRF (scr) as well as Ile-tRF served as specificity controls. The relative amount of the reaction product N-acetyl-[3H]Phe-puromycin (in %) is shown. The product formed in the absence of any tRF (-) was taken as 100%. (b) Val-tRF inhibits peptide bond formation to the same extent regardless if it was added simultaneously with the P-site donor substrate (P) or with the A-site acceptor substrate (A). In all cases, the background values measured in reactions without any ribosomal particles were subtracted from all experimental points. Error bars represent the mean and standard deviation of three to five independent experiments.