σS‐dependent growth‐phase induction of the csgBA promoter in Escherichia coli can be achieved in vivo by σ70 in the absence of the nucleoid‐associated protein H‐NS

Publisher Website
Google Scholar
Abstract
The stationary-phase-specific sigma factor σS (RpoS/KatF) is required for Escherichia coli to induce expression of fibronectin-binding curli organelles upon reaching stationary phase. We show that the csgA gene which encodes the curlin subunit protein belongs to a dicistronic operon, csgBA. The transcriptional start site of csgBA was determined and an AT-rich upstream activating sequence (UAS) required for transcriptional activation was identified. The pcsgBA promoter is not specific for σS since the same promoter sequence can be used by Eσ70in vivo in a strain lacking nucleoid-associated protein H-NS and σS. Transcription remained growth-phase induced and dependent upon the UAS in such a double mutant. Furthermore, we demonstrate that an additional operon, hdeAB, which is also dependent upon σS for transcription, can be transcribed by Eσ70in vivo in the absence of H-NS by utilizing the phdeAB promoter. Two other genes known to be under the control of σS for expression, bolA and katE, remained transcriptionally silent in the absence of H-NS. It is suggested that a subset of E. coli promoters can be recognized by both EσS and Eσ70in vivo but H-NS interacting with these sequences prevents formation of succesful transcription-initiation complexes with Eσ70.