Ribosomes from erythromycin-resistant mutants of Escherichia coli Q13

Abstract

Erythromycin-resistant mutants were isolated by treating Escherichia coli Q13 cells with N-methyl- N'-nitro- N-nitrosoguanidine or 2-aminopurine. The ribosomes from these mutants neither combine appreciably with erythromycin nor perform active peptide synthesis in vitro at the K + NH 4 + concentrations at which erythromycin combines with Q13 ribosomes at a molar ratio of 1 to 1 and where the maximum peptide synthesis is due to the parent Q13 ribosomes. Simply by increasing the environmental K + NH 4 + concentrations the “loss active” ribosomes from erythromycin-resistant mutants can be artificially converted to a state which is active for the binding of erythromycin and peptide synthesis in vitro. Chromatographic analyses of the ribosomal protein components from the mutants on a carboxymethyl-cellulose column showed that a specific protein component 50-8, of the 50 s ribosomal subunits, was altered mutationally and was eluted earlier than the unaltered 50-8 protein of the Q13 strain. In particular, the 50-8 protein from the QE201 mutant was eluted much earlier than that from the other erythromycin-resistant mutants. The QE201 ribosomes require much higher K + NH 4 + concentrations than the other mutant ribosomes to show the maximum ability to bind erythromycin and to carry out active protein synthesis in vitro.