PAS, A NOVEL PROTEIN REQUIRED FOR PROTEIN SECRETION AND ATTACHING ANDEFFACING ACTIVITIES OF ENTEROHEMORRHAGIC ESCHERICHIA-COLI

Enterohemorrhagic Escherichia coli (EHEC) exhibits a pattern of locali zed adherence to host cells, with the formation of microcolonies, and induces a specific histopathological phenotype collectively known as t he attaching and effacing lesion, The genes encoding the products resp onsible for this phenotype are located on a 35-kb pathogenicity island designated the locus of enterocyte effacement, which is also shared b y enteropathogenic E. coli, We have identified an open reading frame ( ORF) which is located upstream of the espA, espB, and espD genes on th e complementary strand and which exhibits high homology to the genes s piB from Salmonella, yscD from Yersinia, and pscD from Pseudomonas. Lo calization studies showed that the encoded product is present in the c ytoplasmic and inner membrane fractions of EHEC. The construction and characterization of a recombinant clone containing an in-frame deletio n of this ORF demonstrated that the encoded product is a putative memb er of a type III system required for protein secretion, Disruption of this ORF, designated pns (protein associated with secretion), abolishe d the secretion of Esp proteins. The mutant adhered only poorly and lo st its capacities to trigger attaching and effacing activity and to in vade HeLa cells, These results demonstrate that Pas is a virulence-ass ociated factor that plays an essential role in EHEC pathogenesis.