The ftsQ1p gearbox promoter of Escherichia coli is a major sigma S-dependent promoter in the ddlB-ftsA region

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The most potent promoters in the ddlB-ftsA region of the dcw cluster have been analysed for σS-dependent transcription. Only the gearbox promoter ftsQ1p was found to be transcribed in vitro by RNA polymerase holoenzyme coupled to σS (EσS). This dependency on σS was also found in vivo when single-copy fusions to a reporter gene were analysed in rpoS and rpoS+ backgrounds. Although ftsQ1p can be transcribed by RNA polymerase containing either σD or σS, there is a preference for EσS when the assay conditions include potassium glutamate and supercoiled templates, a property shared with the bolA1p gearbox promoter. The rest of the promoters assayed, ftsQ2p and ftsZ2p3p4p, similarly to the control bolA2p promoter, were preferentially transcribed by EσD, the housekeeper polymerase. The ftsQ1p and the bolA1p promoters also share the presence of AT-rich sequences upstream of the −35 region and the requirement for an intact wild-type α-subunit for a proficient transcription, allowing their joint classification as gearboxes.

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