Genetic and biochemical characterization of a ribosomal mutant of Bacillus subtilis resistant to sporangiomycin.

The antibiotic sporangiomycin affects the growth of Bacillus subtilis by inhibiting protein synthesis. Mutants of B. subtilis resistant to sporangiomycin have been isolated. One of these, PB 1690, has been further studied. The analysis of subcellular fractions from the mutant has shown that the biochemical effect of the mutation is an alteration of a site on the 50S ribosomal subunit responsible for the binding of the antibiotic: the mutant ribosomes do not bind sporangiomycin and are capable of carrying out phenylalanine polymerization in the presence of sporangiomycin. The resistance mutation maps on the chromosomal region where the ribosomal markers map. The mutant strain is also resistant to the action of the chemically related antibiotic thiostrepton. Treatment of B. subtilis ribosomes with LiCl results in the detachment of a group of proteins including the one responsible for sporangiomycin resistance. Active ribosomes can be reconstructed by mixing "split proteins" and "core particles" of either parental or mutant origin. The fate of the mutant protein can now be followed by assaying reconstructed ribosomes for capacity to bind sporangiomycin and for resistance to the action of the antibiotic in the reactions for phenylalanine polymerization.