Erythromycin resistance due to a mutation in a ribosomal RNA operon of Escherichia coli.

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Abstract
There are 7 rRNA operons (rrn operons) in E. coli. A single rrn operon was amplified by use of a multicopy recombinant plasmid containing a complete rrnH operon. rrnH thereby has the potential to contribute a greater fraction of the rRNA found in ribosomes. Erythromycin-resistant mutants were isolated from cells containing the plasmid, and at least 1 mutation to resistance was shown to reside in rrnH on the plasmid. Erythromycin resistance was retained when a major deletion was introduced into the 16S rRNA gene and was abolished by deletion was introduced into the 16S and 23S rRNA genes but do not alter the 5S rNRA gene or non-rrnH DNA. Cell-free S30 protein-synthesizing extracts from cells containing the mutant plasmid have an increased resistance to erythromycin. The selection procedure used to isolate erythromycin-resistance mutations in rrnH may allow, with minor modifications, the isolation of mutations in rrn operons that change resistance of the ribosome to other antibiotics or that alter other properties or ribosomes.