σE of Streptomyces coelicolor can function both as a direct activator or repressor of transcription

Abstract

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.