Photochemical Cross‐Linking of Elongation Factor G to 70‐S Ribosomes from Escherichia coli by 4‐(6‐Formyl‐3‐azidophenoxy)butyrimidate

Ribosomal proteins situated at or near the binding site of elongation factor G (EF-G) on the Escherichia coli ribosome have been identified by use of the heterobifunctional cross-linker 4-(6-formyl-3-azidophenoxy)butyrimidate. Four different preparations of EF-G, in which the number of cross-linker molecules coupled to EF-G ranged from four to seven, all cross-linked to 50-S subunit proteins L1, L3 and L11 as well as to 30-S subunit proteins S3 and S4. Cross-linking of EF-G to ribosomal proteins was tested electrophoretically. In the case of L7/L12 and L11 immunological methods were also used. Cross-linking of EF-G to L1, L3, L11, S3 and S4 is specific as judged from the fact that addition of unmodified EF-G and of thiostrepton results in less cross-linking. The cross-linking data suggests that the binding site for EF-G includes several proteins which are located at the interface between the 30-S and 50-S subunits.