Phage shock protein, a stress protein of Escherichia coli.

Filamentous phage infection induces the synthesis of large amounts of an Escherichia coli protein, phage shock protein (Psp), the product of a previously undescribed gene. This induction is due to the phage gene IV protein, pIV, an integral membrane protein. The uninduced level of Psp is undetectable, but when induced by prolonged synthesis of pIV, it can become one of the most abundant proteins in the cell. Psp is also synthesized transiently in response to several stresses (heat, ethanol, and osmotic shock). High-level synthesis occurs only after extreme treatment. Unlike the members of the heat shock regulon, Psp induction does not require the heat shock sigma factor, sigma 32; some stimuli that elicit sigma 32-dependent heat shock proteins do not induce Psp synthesis. The level of Psp induction after extreme stress is even higher in sigma 32 mutant cells, which are unable to mount a normal heat shock response, suggesting that these parallel stress responses are interrelated.