Cross‐interaction of anti‐σ H factor RshA with BldG, an anti‐sigma factor antagonist in Streptomyces griseus

Stress‐response sigma factor σ H is negatively regulated by its cognate anti‐sigma factor RshA in Streptomyces griseus . As the overexpression of RshA in the wild‐type strain confers a distinctive bald phenotype (deficiency in aerial mycelium formation and streptomycin production), RshA is supposed to associate with not only σ H but also another regulatory element that plays a crucial role in the developmental control of S. griseus . Here, we show that an anti‐sigma factor antagonist BldG associates with RshA and negatively regulates its activity. The bald phenotype conferred by the overexpression of rshA was restored to the wild‐type phenotype by the coexpression with bldG . The in vivo and in vitro protein interaction analyses demonstrated the specific association between RshA and BldG. A bldG mutant exhibited a distinctive bald phenotype and was defective in the σ H ‐dependent transcription activities. The positive regulatory role of BldG regarding the σ H activity was verified by an in vitro transcriptional analysis, in which the inhibition of σ H ‐dependent transcription by RshA was abolished by the addition of BldG in a dose‐responsive manner. Overall, evidence suggests that BldG serves as a master switch for both stress‐response and developmental gene expression based on its association with multiple anti‐sigma factors in S. griseus .