Multiple functions of I0036 in the regulation of the pathogenicity island of enterohaemorrhagic Escherichia coli O157:H7

摘要

Diarrhoeagenic enterohaemorrhagic Escherichia coli and enteropathogenic E. coli attach to human intestinal epithelium and efface brush-border microvilli, forming an A/E (attaching and effacing) lesion. These human pathogens are phenotypically similar to the mouse pathogen Citrobacter rodentium. Genetically, they all have a homologous set of virulent genes involved in the A/E lesion, and these genes are organized on a LEE (locus of enterocyte effacement), a pathogenicity island. This island comprises 41 specific open reading frames, of which most are organized at five operons, LEE1, LEE2, LEE3, LEE4 and tir (LEE5). The expression of the LEE genes is regulated in a complicated manner, and current knowledge is that there are at least two positive regulators, Ler (LEE-encoded regulator) and GrIA (global regulator of LEE activator), and one negative regulator, called GrIR (global regulator of LEE repressor). In enterohaemorrhagic E. coli, GrIA is encoded by I0043, whereas GrIR is encoded by I0044. Here we report a fourth regulatory gene located in LEE3, namely I0036. Its expression is tightly controlled. When overexpressed, this factor, named Mpc (multiple point controller), interacts with Ler and suppresses the expression of the LEE proteins. When the translation is not initiated or terminated before maturation, the type III secretion of effectors is completely abolished. Therefore, together with the fact that several cis elements reside in the region that I0036 spans, I0036 appeared to have multiple functions in the regulation of LEE expression.