Binding of thiostrepton to ribosomes from thiostrepton-sensitive and -resistant Bacillus subtilis strains

Thiostrepton-resistant mutants exhibit relaxed synthesis of RNA

Spontaneous mutants of Bacillus subtilis resistant to thiostrepton (TSP) exhibit relaxed synthesis of RNA when starved for required amino acids. Intact cells of tsp mutants cannot synthesize the regulatory nucleotides, ppGpp and pppGpp, after amino acid deprivation. Because ribosomes isolated from spontaneous revertants to thiostrepton sensitivity and from wild-type stringent strains can synthesize (p)ppGpp whereas ribosomes isolated from tsp strains cannot synthesize these regulatory nucleotides in the presence of stringent factor, it appears that the lesion is expressed at the level of the ribosome. Genetic mapping, via three-factor transformational crosses, has shown that tsp is closely linked to rif, in the order cysA14, tsp, rif-I, strA. The phenotype of the tsp mutants indicates that they are of the relC type. Their map position indicates that they are different from a previously described B subtilis rel mutation. Ribosomes from the latter strain can synthesize (p)ppGpp in cell-free extracts.

Thiostrepton-resistant mutants of Bacillus subtilis: localization of resistance to the 50S subunit

A number of thiostrepton-resistant mutants of Bacillus subtilis were obtained. The thi mutations map proximally to strA. Effects of thiostrepton on polyphenylalanine synthesis with ribosomes of S-100 fractions from parent and mutant strains indicated that resistance was localized to the ribosomes. Furthermore, effects of thiostrepton on binding of [3H]GTP to ribosomes and 50S subunits from thiostrepton-sensitive and -resistant strains localized the site of resistance to the 50S subunit. In addition, revertants from thiostrepton-resistance to thiostrepton-sensitivity were obtained. Ribosomes and 50S subunits from these thiostrepton-sensitive revertants were sensitive to thiostrepton similar to parental sensitive B. subtilis.