Why does ethanol induce cellular heat-shock response?

Abstract

At the time of induction of the periplasmic protein alkaline phosphatase (AP) in Escherichia coli, the presence of ethanol (10% v/v) in the growth medium did not allow the induced AP to be translocated out to the periplasm. The nontransported AP was stored in the cytoplasm as the unfolded precursor form (AP with its amino-terminal signal sequence), which had no enzymatic activity. The presence of 10% v/v ethanol in the growth medium also induced the heat-shock response in E. coli, which was evident from the enhanced syntheses of several heat-shock proteins (HSPs) over their cellular basal levels. These results, in conjunction with our earlier findings on the occurrence of heat-shock response in an AP-signal sequence mutant of E. coli due to the export deficiency of AP precursor, suggest that the membrane protein precursors, stored in the cytoplasm due to the ethanol-mediated inhibition of translocation, behaved to the cells as abnormal proteins, which ultimately triggered the signal for the induction of heat-shock response in E. coli.