Precursor forms of exported proteins were first accumulated in the envelope of phenethyl alcohol (PEA)-treated cells. After removal of PEA, a complete processing could be obtained in a few minutes. In this work, we demonstrate that colicins A and E1, that act on the electrical gradient in the cytoplasmic membrane, prevent the processing of precursor forms previously accumulated. Concentrations of colicins accounting for ∼1 killing unit (50–3000 molecules/cell) were found to be sufficient for inhibition of processing. Therefore our results strongly suggest that in intact cells the electrical gradient across the cytoplasmic membrane is required for maturation of exported proteins.
