The Escherichia coli Regulator of Sigma 70 Protein, Rsd, Can Up-Regulate Some Stress-Dependent Promoters by Sequestering Sigma 70

ABSTRACT

The Escherichia coli Rsd protein forms complexes with the RNA polymerase σ⁷⁰ factor, but its biological role is not understood. Transcriptome analysis shows that overexpression of Rsd causes increased expression from some promoters whose expression depends on the alternative σ³⁸ factor, and this was confirmed by experiments with lac fusions at selected promoters. The LP18 substitution in Rsd increases the Rsd-dependent stimulation of these promoter-lac fusions. Analysis with a bacterial two-hybrid system shows that the LP18 substitution in Rsd increases its interaction with σ⁷⁰. Our experiments support a model in which the role of Rsd is primarily to sequester σ⁷⁰, thereby increasing the levels of RNA polymerase containing the alternative σ³⁸ factor.