Erythromycin resistance mutations in ribosomal proteins L22 and L4 perturbthe higher order structure of 23 S ribosomal RNA

We have used chemical modification to examine the conformation of 23 S rRNA in Escherichia coli ribosomes bearing erythromycin resistance mutations in ribosomal proteins L22 and L4. Changes in reactivity to chemical probes we re observed at several nucleotide positions scattered throughout 23 S rRNA. The L4 mutation affects the reactivity of G799 and U1255 in domain II and that of A2572 in domain V. The L22 mutation influences modification in doma in II at positions m(5)U747, G748, and A1268, as well as at A1614 in domain III and G2351 in domain V. The reactivity of A789 is weakly enhanced by bo th the L22 and L4 mutations. None of these nucleotide positions has previou sly been associated with macrolide antibiotic resistance. Interestingly, ne ither of the ribosomal protein mutations produces any detectable effects at or within the vicinity of A2058 in domain V, the site most frequently show n to confer macrolide resistance when altered by methylation or mutation. T hus, while L22 and L4 bind primarily to domain 1 of 23 S rRNA, erythromycin resistance mutations in these ribosomal proteins perturb the conformation of residues in domains II, III and V and affect the action of antibiotics k nown to interact with nucleotide residues in the peptidyl transferase cente r of domain V. These results support the hypothesis that ribosomal proteins interact with rRNA at multiple sites to establish its functionally active three-dimensional structure, and suggest that these antibiotic resistance m utations act by perturbing the conformation of rRNA. (C) 1999 Academic Pres s.