σ E of Streptomyces coelicolor can function both as a direct activator or repressor of transcription.

σ factors are considered as positive regulators of gene expression. Here we reveal the opposite, inhibitory role of these proteins. We used a combination of molecular biology methods and computational modeling to analyze the regulatory activity of the extracytoplasmic σ E factor from Streptomyces coelicolor. The direct activator/repressor function of σ E was then explored by experimental analysis of selected promoter regions in vivo. Additionally, the σ E interactome was defined. Taken together, the results characterize σ E , its regulation, regulon, and suggest its direct inhibitory function (as a repressor) in gene expression, a phenomenon that may be common also to other σ factors and organisms.