Stress-induced expression of the Escherichia coli phage shock protein operon is dependent on sigma 54 and modulated by positive and negative feedback mechanisms.

Abstract

The phage shock protein (psp) operon of Escherichia coli is strongly induced in response to heat, ethanol, osmotic shock, and infection by filamentous bacteriophages. The operon contains at least four genes--pspA, pspB, pspC, and pspE--and is regulated at the transcriptional level. We report here that psp expression is controlled by a network of positive and negative regulatory factors and that transcription in response to all inducing agents is directed by the or-factor r s4. Negative regulation is mediated by both PspA and the r heat shock proteins. The PspB and PspC proteins cooperatively activate expression, possibly by antagonizing the PspA-controlled repression. The strength of this activation is determined primarily by the concentration of PspC, whereas PspB enhances but is not absolutely essential for PspC-dependent expression. PspC is predicted to contain a leucine zipper, a motif responsible for the dimerization of many eukaryotic transcriptional activators. PspB and PspC, though not necessary for psp expression during heat shock, are required for the strong psp response to phage infection, osmotic shock, and ethanol treatment. The psp operon thus represents a third category of transcriptional control mechanisms, in addition to the r 32-and erE-dependent systems, for genes induced by heat and other stresses.[Key Words: Phage shock protein; stress response; heat shock; cr54; filamentous bacteriophage; leucine zipper] Received June 20, 1991; revised version accepted August 15, 1991.Exposure to certain adverse environmental conditions, such as high temperature, causes all organisms to coordinately and vigorously induce the synthesis of a specific set of proteins called the heat shock proteins (HSPs; for reviews, see Lindquist and Craig 1988;Gross et al. 1990). This phenomenon, the heat shock response, is the product of perhaps the best conserved and most universal genetic network. Similarities in this response between prokaryotes and eukaryotes include the sequences of certain HSPs (e.g., the 90-, 70-, and 60-kD HSP families), the treatments that stimulate the response (e.g., heat, ethanol, heavy metal ions), and the large, rapid increases in heat shock gene transcription that follow environmental challenge. In Escherichia coli, previous work in several laboratories identified at least two mechanisms of transcriptional control for heat shock gene expression. Most of the detected heat shock genes (-17)

PspF and IHF bind co‐operatively in the psp promoter‐regulatory region of Escherichia coli

“…Bacterial strains and plasmids E. coli strains K561 [HfrC þ relA1 spoT1 T 2 r (ompF627 fadL701 ) lacI q ] (Davis et al, 1985), K1527 (K561 pspF ::mTn10-tet (pspF 877 ) (Tc r )) (Jovanovic et al, 1996), K1247 (PK2212) (⌬kdpABC-5 thi-1 ⌬trkE tet s rha4 lacZ48 gal-33 malA35 zci-233::Tn10 ⌬aldH-ordL-goaG-pspF-pspA-E r ¹ ) , K1173 (W3110 [K-12 ¹ IN (rrnD -rrnE )]str R himA⌬82::Tn10 himD⌬3::cam (Cm r )) (Greenstein et al, 1988), L57 (K561 rpoN::Tn10 (Tc r )) (Weiner et al, 1991) and L108 (K561 himD⌬3::cam (Cm r )) (L. Weiner, unpublished results) have been described previously. E. coli strains were grown at 37ЊC in rich Luria-Bertani (LB) medium.…”

“…These earlier results are specific to the promoters studied; there is no reason in principle why the specific organization of regulatory elements in a 54 -dependent promoter region should not facilitate co-operative binding of the activator, IHF, and polymerase. Results from in vivo experiments suggest that IHF might influence the binding of PspF , the activator of the Escherichia coli phageshock protein (psp ) operon (pspA-E ) in which transcription is also 54 dependent (Weiner et al, 1991).…”

The Escherichia coli phage‐shock‐protein (psp) operon

“…PspA acts as a negative regulator, while PspB and C act in concert as positive regulators, by relieving the repression imposed by PspA Weiner et al, 1991;) (see Fig. 2).…”

“…In addition, PspA protein is a major component of the limited protein synthesis that occurs during late stationary phase (Weiner and Model, 1994). Other than expression of gene IV or infection with filamentous phage, all the inducing stimuli also induce the 32 -dependent heat-shock genes (groE, dnaK, dnaJ, grpE (Lindquist and Craig, 1988;Yura et al, 1993)), but psp-operon transcription does not require 32 and hence none of the other components of the canonical heat-shock response; indeed, shift of a 32ts mutant to the non-permissive temperature intensifies the psp response, and for the stimuli that induce psp transiently, such as heat and exposure to ethanol, this prolongs the response (Brissette et al, 1990;Weiner et al, 1991). A participant in the canonical heatshock response of E. coli is E , which is responsible for transcription of 32 at 50ЊC (Erickson and Gross, 1989) and is itself activated by overproduction of outer membrane proteins (Mecsas et al, 1993).…”

Role of an Escherichia coli stress-response operon in stationary-phase survival.

“…strains in the alkaline medium, and stationary-phase survival of the psp mutants improves substantially at pH values closer to the optimal growth range (pH [6][7][8]. In late statoar-phase (1-to 2-day-old) cells, the operon can be strongly induced under certain conditions, and PspA can become one ofthe most highly expressed bacterial proteins.…”