Transcriptional Organization and In Vivo Role of theEscherichia coli rsd Gene, Encoding the Regulator of RNA Polymerase Sigma D

ABSTRACT The regulator of sigma D (Rsd) was identified as an RNA polymerase ς70-associated protein in stationary-phaseEscherichia coli with the inhibitory activity of ς70-dependent transcription in vitro (M. Jishage and A. Ishihama, Proc. Natl. Acad. Sci. USA 95:4953–4958, 1998). Primer extension analysis of rsd mRNA indicated the presence of two promoters, ςS-dependent P1 and ς70-dependent P2 with the gearbox sequence. To get insight into the in vivo role of Rsd, the expression of a reporter gene fused to either the ς70- or ςS-dependent promoter was analyzed in the absence of Rsd or the presence of overexpressed Rsd. In the rsd null mutant, the ς70- and ςS-dependent gene expression was increased or decreased, respectively. On the other hand, the ς70- or ςS-dependent transcription was reduced or enhanced, respectively, after overexpression of Rsd. The repression of the ςS-dependent transcription in the rsd mutant is overcome by increased production of the ςS subunit. Together these observations support the prediction that Rsd is involved in replacement of the RNA polymerase ς subunit from ς70 to ςS during the transition from exponential growth to the stationary phase.