IDENTIFICATION, NUCLEOTIDE-SEQUENCE, AND CHARACTERIZATION OF PSPF, THE TRANSCRIPTIONAL ACTIVATOR OF THE ESCHERICHIA-COLI STRESS-INDUCED PSPOPERON

The phage shock protein (psp) operon (pspABCE) of Escherichia coli is strongly induced in response to a variety of stressful conditions or a gents such as filamentous phage infection, ethanol treatment, osmotic shock, heat shock, and prolonged incubation in stationary phase. Trans cription of the psp operon is driven from a sigma(54) promoter and sti mulated by integration host factor. We report here the identification of a transcriptional activator gene, designated pspF, which controls e xpression of the psp operon in E. coli. The pspF gene was identified b y random miniTn10-tet transposon mutagenesis. Insertion of the transpo son into the pspF gene abolished sigma(54)-dependent induction of the psp operon. The pspF gene is closely linked to the psp operon and is d ivergently transcribed from one major and two minor sigma(70) promoter s. pspF encodes a 37-kDa protein which belongs to the enhancer-binding protein family of sigma(54) transcriptional activators. PspF contains a catalytic domain, which in other sigma(54) activators mould be the central domain, and a C-terminal DNA-binding domain but entirely lacks an N-terminal regulatory domain and is constitutively active. The ins ertion mutant pspF::mTn10-tet (pspF(877)) encodes a truncated protein (PspF Delta HTH) that lacks the DNA-binding helix-turn-helix (HTH) mot if. Although the central catalytic domain is intact, PspF Delta HTH at physiological concentration cannot activate psp expression. In the ab sence of inducing stimuli, multicopy-plasmid-borne PspF or PspF Delta HTH overcomes repression of the psp operon mediated by the negative re gulator PspA.