PHYSIOLOGICAL AND BIOCHEMICAL-ANALYSIS OF THE EFFECTS OF ALKALINE-PHOSPHATASE OVERPRODUCTION IN ESCHERICHIA-COLI

Overexpression of the Escherichia coli phoA gene, coding for alkaline phosphatase (PhoA), on multicopy plasmids caused a severe defect in th e precursor processing (secretion) of PhoA, beta-lactamase, and the ou ter membrane protein OmpA, This secretion defect continued even after the repression of phoA expression, indicating that protein secretion w as irreversibly impaired in cells, Among the secretory proteins, only OmpA gradually secreted posttranslationally. The inverted inner membra ne vesicles prepared from cells with the secretion defect showed appre ciably reduced translocation activity in vitro, But the membrane vesic les retained the ability to generate a proton motive force which, toge ther with ATP, is essential as an energy source for the efficient secr etion of proteins in E. coli, An appreciable amount of incompletely tr anslocated PhoA molecules was detected in the inner membranes of cells with the secretion defect.