Streptomyces coelicolor produces four genetically and structurally distinct antibiotics in a growth-phase-dependent manner.S. coelicolor mutants globally deficient in antibiotic production (Abs− phenotype) have previously been isolated, and some of these were found to define the absB locus. In this study, we isolated absB-complementing DNA and show that it encodes the S. coelicolor homolog of RNase III (rnc). Several lines of evidence indicate that theabsB mutant global defect in antibiotic synthesis is due to a deficiency in RNase III. In marker exchange experiments, the S. coelicolor rnc gene rescued absB mutants, restoring antibiotic production. Sequencing the DNA of absB mutants confirmed that the absB mutations lay in thernc open reading frame. Constructed disruptions ofrnc in both S. coelicolor 1501 andStreptomyces lividans 1326 caused an Abs−phenotype. An absB mutation caused accumulation of 30S rRNA precursors, as had previously been reported for E. coli rncmutants. The absB gene is widely conserved in streptomycetes. We speculate on why an RNase III deficiency could globally affect the synthesis of antibiotics.
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