A Carboxy-Terminal 16-Amino-Acid Region of ς(38) of Escherichia coli Is Important for Transcription under High-Salt Conditions and Sigma Activities In Vivo

ς(38) (or ς(S), the rpoS gene product) is a sigma subunit of RNA polymerase in Escherichia coli and directs transcription from a number of stationary-phase promoters as well as osmotically inducible promoters. In this study, we analyzed the function of the carboxy-terminal 16-amino-acid region of ς(38) (residues 315 to 330), which is well conserved among the rpoS gene products of enteric bacterial species. Truncation of this region was shown to result in the loss of sigma activity in vivo using promoter-lacZ fusion constructs, but the mutant ς(38) retained the binding activity in vivo to the core enzyme. The in vitro transcription analysis revealed that the transcription activity of ς(38) holoenzyme under high potassium glutamate concentrations was significantly decreased by the truncation of the carboxy-terminal tail element.