TetR family member PsrA directly binds the Pseudomonas rpoS and psrA promoters

We have previously described a Pseudomonas gene, psrA, which enhances transcription of the rpoS sigma factor gene at stationary phase. We present molecular data which demonstrate that in Pseudomonas putida PsrA binds specifically to the rpoS and psrA promoters in DNA regions having similar palindromic sequences, C/GAAAC N2-4 GTTTG/C, where N is any nucleotide. The position of the initiation of transcription was determined for both promoters, and PsrA binds from positions - 59 to -35 in the rpoS promoter and from - 18 to + 20 in the psrA promoter with respect to the +1 transcription site. Expression studies with a psrA-lacZ transcriptional fusion in wild-type and psrA::Tn5 knockout mutants revealed that psrA was under additional control in response to growth phase. A model for the role of PsrA in the regulation of rpoS and psrA is presented.