Fig. (4) Poly(U)-dependent poly(Phe) synthesis activity of E. coli 70S ribosomes reconstituted with mutant rps (L7/L12)₂. Purified E. coli 30S subunits (0.65 µM) and purified 50S subunits (0.65 µM) untreated or depleted from rp bL12 were incubated for 10 min at 37°C in the presence of 10 µM purified wild type or mutated rps bL12. The experimental conditions were the same as in Fig. (3).