SIGMA(S)-DEPENDENT GROWTH-PHASE INDUCTION OF THE CSGBA PROMOTER IN ESCHERICHIA-COLI CAN BE ACHIEVED IN-VIVO BY SIGMA(70) IN THE ABSENCE OF THE NUCLEOID-ASSOCIATED PROTEIN H-NS

The stationary-phase-specific sigma factor sigma(S) (RpoS/KatF) is req uired for Escherichia coli to induce expression of fibronectin-binding curli organelles upon reaching stationary phase. We show that the csg A gene which encodes the curlin subunit protein belongs to a dicistron ic operon, csgBA. The transcriptional start site of csgBA was determin ed and an AT-rich upstream activating sequence (UAS) required for tran scriptional activation was identified. The pcsgBA promoter is not spec ific for sigma(S) since the same promoter sequence can be used by E si gma(70) in vivo in a strain lacking nucleoid-associated protein H-NS a nd sigma(S). Transcription remained growth-phase induced and dependent upon the UAS in such a double mutant. Furthermore, we demonstrate tha t an additional operon, hdeAB, which is also dependent upon sigma(S) f or transcription, can be transcribed by E sigma(70) in vivo in the abs ence of H-NS by utilizing the phdeAB promoter. Two other genes known t o be under the control of sigma(S) for expression, bolA and katE, rema ined transcriptionally silent in the absence of H-NS. It is suggested that a subset of E. coli promoters can be recognized by both E sigma(S ) and E sigma(70) in vivo but H-NS interacting with these sequences pr events formation of succesful transcription-initiation complexes with E sigma(70).