INVOLVEMENT OF STRESS PROTEIN PSPA (PHAGE SHOCK PROTEIN-A) OF ESCHERICHIA-COLI IN MAINTENANCE OF THE PROTONMOTIVE FORCE UNDER STRESS CONDITIONS

The expression of specific PhoE mutant proteins leads to induction of the expression of the psp operon of Escherichia coil and the export of various plasmid-encoded precursors is retarded in a pspA mutant strai n, Here. we have investigated the specific role of various Psp protein s in the export process. PspB and PspC are both inner membrane protein s that are involved in the regulation of the transcription of the psp operon, Precursor PhoE translocation was retarded in a pspB mutant str ain to a similar extent as in a pspA mutant strain, The reduced transl ocation efficiencies in the various psp mutants could be complemented by expression of PspA from a plasmid, indicating that only PspA is req uired for efficient translocation, Mutant prePhoE proteins that can be translocated independently of the Delta mu H+ appeared to translocate equally efficiently in a wild-type and in a pspA mutant strain. Furth ermore, quantitative in vivo determination of the Delta mu H+ showed t hat it specifically decreased in a pspA mutant strain upon expression of plasmid-encoded (mutant) prePhoE protein, Apparently, the transloca tion defects observed in a psp mutant strain are caused by a decrease of the Delta mu H+ and PspA functions by maintaining the Delta mu H+ u nder these conditions.