Activation of antibiotic biosynthesis by specified mutations in the rpoB gene (encoding the RNA polymerase β subunit) of Streptomyces lividans

We found that the biosynthesis of actinorhodin (Act), undecylprodigiosin (Red), and calcium-dependent antibiotic (CDA) are dramatically activated by introducing certain mutations into the rpoB gene that confer resistance to rifampin to Streptomyces lividans 66, which produces less or no antibiotics under normal growth conditions. Activation of Act and/or Red biosynthesis by inducing mutations in the rpoB gene was shown to be dependent on the mutation's position and the amino acid species substituted in the beta-subunit of the RNA polymerase. Mutation analysis identified 15 different kinds of point mutations, which are located in region I, II, or III of the rpoB gene and, in addition, two novel mutations (deletion of nucleotides 1287 to 1289 and a double substitution at nucleotides 1309 and 1310) were also found. Western blot analyses and S1 mapping analyses demonstrated that the expression of actII-ORF4 and redD, which are pathway-specific regulatory genes for Act and Red, respectively, was activated in the mutants able to produce Act and Red. The ActIV-ORF1 protein (an enzyme for Act biosynthesis) and the RedD protein were produced just after the upregulation of ActII-ORF4 and RedZ, respectively. These results indicate that the mutation in the rpoB gene of S. lividans, resulting in the activation of Act and/or Red biosynthesis, functions at the transcription level by activating directly or indirectly the key regulatory genes, actII-ORF4 and redD. We propose that the mutated RNA polymerase may function by mimicking the ppGpp-bound form in activating the onset of secondary metabolism in Streptomyces.