Cross-interaction of anti-σH factor RshA with BldG, an anti-sigma factor antagonist in Streptomyces griseus

Abstract

Stress-response sigma factor σH 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 σH 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 σH-dependent transcription activities. The positive regulatory role of BldG regarding the σH activity was verified by an in vitro transcriptional analysis, in which the inhibition of σH-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. © 2010 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.