Fig. 3. The effects of G-nucleotides and IF2 concentration on the rate of peptidyl transfer, starting from pre-initiation 30S complexes and 50S subunits. Subunits were mixed in the presence of IFC and either GTP (diamonds), GDP (triangles) or GDPNP (squares). The reaction mixture contained either 2.5 pmol IF2 (A) or 120 pmol IF2 (B) per 50 pmol of ribosomes. The extent of ribosome initiation was monitored by dipeptide formation. Ternary complexes (EF-Tu–GTP–Phe-tRNAP^he) were added at different time points after subunit mixing, and the peptidyl-transfer reaction was quenched with 50% formic acid after 5 s.