Direct cross-linking of heptauridilate to E. coli ribosomes by water-soluble carbodiimide in the complex stabilized by codon-anticodon interaction at both A- and P-sites

Affinity labelling of E. coli ribosomes is performed by treatment with water-soluble carbodiimide of the complex of ribosomes with (pU)7, tRNAPhe at the P-site and with Phe-tRNAPhe (complex I) and without Phe-tRNAPhe (complex II) at the A-site. The extent of modification is, respectively, 0.06 and 0.026 mol (pU)7 per mol ribosomes. Protein S3 is found as a single labelled protein in complex I, whereas S7, S8, L25 are modified in complex II. Thus, in the absence of a large spacer group within the complex stabilized by codon-anticodon interactions at both A- and P-sites, a highly selective modification occurs.