Efficient export of alkaline phosphatase overexpressed from a multicopy plasmid requires degP, a gene encoding a periplasmic protease of Escherichia coli

Escherichia coli DegP is an inducible serine protease which is involved in the breakdown of abberant proteins arising in the periplasmic compartment. Overexpression of alkaline phosphatase (PhoA) increased transcription of de gP by twofold. To examine the significance of its induction, we overexpress ed PhoA in a mutant strain deficient in the degP gene. Upon PhoA overexpres sion, the degP mutant produced a smaller amount of active PhoA, about one h alf of the enzymatic activity of its isogenic wild-type strain, and accumul ated a larger amount of its precursor, indicating that degP is required for efficient export of overexpressed PhoA. Pulse-chase experiment showed that PhoA overexpression in the absence of degP causes a severe defect in the e xport of several proteins tested. Examination of the synthesis and the accu mulation of the phoA gene products revealed that a part of them, synthesize d in the wild-type strain, undergoes relatively rapid proteolysis and that degP is necessary for such a process. From these results, we discuss a poss ible role of DegP in facilitating protein export under stress conditions.