Temperature Regulation of Heat-Labile Enterotoxin (LT) Synthesis in Escherichia coli Is Mediated by an Interaction of H-NS Protein with the LT A-Subunit DNA

Protein and mRNA levels of heat-labile enterotoxin (LT) of Escherichia coli are highest at 37°C, and they decrease gradually as temperature is decreased. This temperature effect is eliminated in an Hns(−) mutant. Deletion of portions of DNA coding for the LT A subunit also results in an increase in LT expression at low temperatures, suggesting that the H-NS protein causes inhibition of transcription at low temperatures by interacting with the LT A-subunit DNA. The region that interacts with H-NS is referred to as the downstream regulatory element (DRE). Plasmids in an hns strain from which the DRE has been deleted still produce elevated levels of LT at 18°C, suggesting that intact DRE is not required for transcription from the LT promoter.