Thermoregulated expression of virulence genes in enteropathogenic Escherichia coli.

Enteropathogenic Escherichia coli (EPEC) causes severe diarrhoea in young children. The locus of enterocyte effacement (LEE) pathogenicity island comprises a cluster of operons encoding a type III secretion system and related proteins that are associated with EPEC virulence. The LEE1 operon encodes Ler that positively regulates the LEE2, LEE3, LEE4, LEE5 and espG transcriptional units. The LEE operons are repressed at 27 degrees C and expressed at 37 degrees C. This paper describes a regulatory cascade of the thermoregulation of LEE operons. LEE1 including ler is repressed by H-NS at 27 degrees C but not at 37 degrees C. In contrast, the expression of the LEE2, LEE3, LEE4, LEE5 and espG transcriptional units is repressed by H-NS at both 27 degrees C and 37 degrees C. Upon shifting the culture temperature from 27 degrees C to 37 degrees C, Ler is synthesized and in turn activates the expression of LEE2, LEE3, LEE4 and espG by releasing the H-NS mediated repression. In the case of LEE5, Ler acts both by alleviating the H-NS mediated repression and by an additional mechanism, as yet to be defined.