30SIC, containing increasing concentrations of IF3, was rapidly mixed with 3.0 μM 50S ribosomal subunits. IF3 concentrations were: 3.0 μM, red trace; 1.5 μM, blue trace; 0.45 μM, green trace; 0.225 μM brown trace; no IF3, grey trace. Other 30SIC components were employed at the standard final concentrations described in Materials and Methods.