The effect of IHF on σS selectivity of the phoA and pst promoters of Escherichia coli
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The pst operon, a member of the PHO regulon of Escherichia coli, encodes a high-affinity phosphate transport system whose expression is induced when the cells enter a phase of phosphate starvation. The expression of pst is stimulated by the integration host factor (IHF). Transcription of the PHO regulon genes is initiated by the RNA polymerase complexed with σD (EσD). Owing to a cytosine residue at position −13 of the pst promoter its transcription can also be initiated by EσS. Here, we show that inactivation of IHF in vivo abolishes the σS-dependent transcription initiation of the pst operon, indicating that both −13C residue and IHF are required to confer on pst the ability to be transcribed by EσS. Introduction of a −13C residue in the promoter region of phoA, another PHO regulon gene that is not directly affected by IHF, did not affect its exclusive transcription initiation by EσD.
KeywordsPHO regulon pst operon IHF rpoS Escherichia coli
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