Life Science Research Center, College of Bioresource Sciences, Nihon University, Fujisawa, Japan.
FEMS Microbiol Lett. 2011 Jan;314(2):158-63. doi: 10.1111/j.1574-6968.2010.02155.x. Epub 2010 Dec 14.
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.
在灰色链霉菌中，应激反应σ（H）因子受其同源反σ因子 RshA 的负调控。由于 RshA 在野生型菌株中的过表达赋予了独特的光秃表型（缺乏气生菌丝形成和链霉素产生），因此 RshA 不仅与σ（H）因子，而且与另一个在灰色链霉菌发育调控中起关键作用的调节元件结合。在这里，我们表明一种反σ因子拮抗剂 BldG 与 RshA 结合，并负调控其活性。过表达 rshA 赋予的光秃表型通过与 bldG 的共表达恢复为野生型表型。体内和体外蛋白相互作用分析表明 RshA 和 BldG 之间存在特异性结合。bldG 突变体表现出独特的光秃表型，并且在 σ（H）依赖性转录活性中存在缺陷。通过体外转录分析验证了 BldG 对 σ（H）活性的正调控作用，其中 RshA 对 σ（H）依赖性转录的抑制作用被 BldG 以剂量反应方式消除。总的来说，证据表明 BldG 作为灰色链霉菌中多个反σ因子的结合物，基于其与多个反σ因子的结合，作为应激反应和发育基因表达的主开关。
