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

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Abstract
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.