Overproduction and purification of sigmaS, the Escherichia coli stationary phase specific sigma transcription factor

This paper reports the overproduction and the details of a rapid method to purify active sigmaS monomers from a T7 RNA polymerase-based protein expression system. This 2-day procedure involves solubilizing inclusion bodies in sarkosyl detergent, removal of sarkosyl by dialysis, and a single gel filtration column chromatography step. The final yield of sigmaS is about 9 mg of approximately 92% purity from 0.5 g of wet weight cells. Overproduced sigmaS binds to core RNA polymerase and supports transcription from the bolAp1 promoter, a sigmaS-dependent promoter.