Fluorescent Labels on Ribosomes

70‐S ribosomes have three binding sites for the dimer of 1‐anilino‐8‐naphthalenesulfonate, a specific ligand for proteins. Synthesis of polyphenylalanine is not inhibited by the fixation of three dye molecules per ribosome. At low concentration of Mg2+, four and two molecules of dye can bind respectively to 50‐5 and 30‐S ribosomal particles and reassociation to functional ribosomes is always possible when the Mg2+ content is increased. These variations of the average number of binding sites are interpreted as being due to a conformational modification induced by Mg2+. Activity for protein synthesis and spectroscopic properties of ribosomes covalently bound to the carcinogen 7‐methylbenz[a]anthracene which is specific for ribosomal RNA Are Also described and polarisation studies of the ternary complex ribosome, mRNA, tRNA using a poly(A) labeled with the same compound indicates the mobility of the messenger in this complex.