title: Fluorescent labelling of Escherichia coli ribosomal sulfhydryl groups.
abstract: The reactivity of the sulfhydryl groups of Escherichia coli ribosome has been investigated using a fluorescent label. Under denaturing conditions, all the --SH groups can be titrated. In the native form of the ribosome, six and less than one labels can be respectively conjugated to the 30-S and 50-S subparticles without loss of activity for poly(U)-dependent polyphenylalanine synthesis. The most reactive thiol groups belong to proteins S1, S12, S18, S21. The binding of mRNA plus tRNA to the 70-S ribosomes affects the spectroscopic properties of the labels showing that conformational changes are induced by these interactions. Furthermore, the treatment of these complexes by the labelling agent demonstrates that the --SH group belonging to protein S1 is partially protected whereas other thiol groups located on the 50-S subparticle become reactive.
mesh_terms: D001665:Binding Sites; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D005033:Ethylmaleimide / Q000494:pharmacology; D005456:Fluorescent Dyes; D007700:Kinetics; D012269:Ribosomal Proteins / Q000032:analysis; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000032:analysis; D014508:Urea
chemical_list: D005456:Fluorescent Dyes; D012269:Ribosomal Proteins; D013438:Sulfhydryl Compounds; D014508:Urea; D004228:Dithionitrobenzoic Acid; D005033:Ethylmaleimide