Affinity labeling of Escherichia coli ribosomes with a covalently binding derivative of the antibiotic pleuromutilin

Reaction of an alkylating pleuromutilin derivative with E. coli ribosomes led to the binding of the compound to both proteins and RNA. If ribosomes of the E. coli strain MRE600 were used, mainly S18 and L2 became labeled. Ribosomes from E. coli D10 bound the reagent to S18 and frequently to L27 instead of L2. Possibly at slight difference in the structure of these ribosomes exposes different, although closely neighboring, L proteins to the reagent. The simultaneous labeling of L and S proteins seems to reflect the presence of two binding sites for the antibiotic and indicates that the binding sites are located at the interphase region between large and small ribosomal subunits. Analysis of the RNA showed that the affinity label is mainly attached to the 23S species. These data are in good agreement with the known effects of pleuromutilin derivatives on ribosomal functions.