Elongation factor G and protein S12 are the nearest neighbours in the Escherichia coli ribosome

It has been found that iodine oxidation of the complex of ribosomes with EF-G † results in the formation of a disulphide bond between the single exposed sulphydryl group of the factor and each of the ribosomal subunits. It is concluded that this EF-G region is localized on the ribosomal interface. Protein S12 is identified as the ribosomal component crosslinked with EF-G in the oxidation reaction. The possible role of the specific interaction of EF-G with protein S12 for the functioning of the factor as an activator of translocation is discussed.