The locus of enterocyte effacement-encoded regulator (Ler) is a regulatory protein that controls bacterial pathogenicity of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic Escherichia coli (EHEC). More specifically, Ler regulates the locus of enterocyte effacement (LEE) pathogenicity island genes, which are responsible for creating intestinal attachment and effacing lesions and subsequent diarrhea: LEE1, LEE2, and LEE3. LEE1, 2, and 3 carry the information necessary for a type III secretion system. The transcript encoding the Ler protein is the open reading frame 1 on the LEE1 operon.
The mechanism of Ler regulation involves competition with histone-like nucleoid structuring protein (H-NS), a negative regulator of the LEE pathogenicity island. Ler is regulated by many factors such as plasmid encoded regulator (Per), integration host factor, Fis, BipA, a positive regulatory loop involving GrlA, and quorum sensing mediated by luxS.
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