ANALYSIS OF THE PROTEINS AND CIS-ACTING ELEMENTS REGULATING THE STRESS-INDUCED PHAGE SHOCK PROTEIN OPERON

The phage shock protein operon (pspABCE) of Escherichia coil is strong ly induced by adverse environmental conditions, Expression is controll ed principally at the transcriptional level, and transcription is dire cted by the sigma factor sigma(54), PspB and PspC are required for hig h-level psp expression during osmotic shock, ethanol treatment and f1 infection, but heat-induced expression is independent of these protein s, We report here that the promoter region contains an upstream activa tion sequence (UAS) that is required for psp induction and has the enh ancer-like ability to activate at a distance, A DNA-binding activity i s detected in crude protein extracts that is dependent on the UAS and induced by heat shock, We further shaw that integration host factor (I HF) binds in vitro to a site between the UAS and sigma(54) recognition sequence, In bacteria lacking IHF, psp expression is substantially re duced in response to high temperature and ethanol, During osmotic shoc k in contrast, psp expression is only weakly stimulated by IHF, and IH F mutants can strongly induce the operon, The dependence of psp expres sion on IHF varies with the inducing condition, but does not correlate with dependence on PspB and PspC, indicating distinct, agent-specific activation mechanisms.