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 degrees 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,vith 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 degrees C, suggesting that intact DRE is not required for transcription from the LT promoter.