Expression of ribosomal protein genes as analyzed by bacteriophage Mu-induced mutations

The organization of ribosomal protein genes and the gene (fus) for a protein chain elongation factor, EF G, in Escherichia coli were studied with a merodiploid strain that has an episome with genetic markers, ery(r), spc(r), str(r), and fus(r), and a chromosome with markers ery(s), spc(s), str(s), and fus(s). The ery locus determines a 50S ribosomal protein and the spc and str loci determine 30S ribosomal proteins. The phenotype of the diploid strain is sensitive to all of the four antibiotics, erythromycin (Ery), spectinomycin (Spc), streptomycin (Str), and fusidic acid (Fus). Analysis of antibiotic-resistant mutants induced by bacteriophage Mu in the diploid strain indicates that these four genes, and probably many other ribosomal protein genes linked to them, are transcribed as a single unit, and the direction of the transcription is in the order of ery, spc, str, and fus.