Abstract
Both rRNA and protein components of Escherichia coli ribosomes have been specifically labelled without any important loss of activity for polyphenylalanine synthesis in the cell‐free system. Three adenylic residues per 70‐S ribosome were labelled by an anthracenyl derivative and the ribosomal proteins by dansylation of four amino acid residues per 70‐S particle. The association between the two complementary subparticles, the formation of the binary and ternary complexes in the presence of mRNA and tRNA were investigated using the concomitant measuring of fluorescence intensity and polarisation of the two kinds of labels. The formation of these complexes involves the rRNA and the ribosomal protein components of the 30‐S and 50‐S sub‐particles directly and/or indirectly. The mobility of the messenger bound to the 70‐S ribosome in the presence of tRNA is indicated by use of a polyadenylic acid labelled with the same marker as that for rRNA. Reversible conformational changes are observed during acidic‐alkaline titrations and melting curves of fluorescent ribosomal particles. The irreversible denaturation occurs at the same pH and melting temperature for the rRNA and the ribosomal components: The results are interpreted in terms of highly specific interactions between the rRNA and the proteins, slight modification in the strength and/or nature of these interactions leading to a conformational change of the whole ribosomal particle.
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