Transcriptional organization and in vivo role of the Escherichia coli rsd gene, encoding the regulator of RNA polymerase sigma D

The regulator of sigma D (Rsd) was identified as an RNA polymerase sigma(70 )-associated protein in stationary-phase Escherichia coli with the inhibito ry activity of sigma(70)-dependent transcription in vitro (M, Jishage and A , Ishihama, Proc. Natl. Acad, Sci, USA 95:4953-1958, 1998), Primer extensio n analysis of rsd mRNA indicated the presence of two promoters, sigma(S)-de pendent P1 and sigma(70)-dependent P2 with the gearbox sequence, To get ins ight into the in vivo role of Rsd, the expression of a reporter gene fused to either the sigma(70)- or as dependent promoter was analyzed in the absen ce of Rsd or the presence of overexpressed Rsd. In the rsd null mutant, the sigma(70)- and sigma(S)-dependent gene expression was increased or decreas ed, respectively. On the other hand, the sigma(70)- or sigma(S)-dependent t ranscription was reduced or enhanced, respectively, after overexpression of Rsd, The repression of the sigma(S)-dependent transcription in the rsd mut ant is overcome by increased production of the sigma(S) subunit. Together t hese observations support the prediction that Rsd is involved in replacemen t of the RNA polymerase sigma subunit from sigma(70) to sigma(S) during the transition from exponential growth to the stationary phase.