ENTEROPATHOGENIC ESCHERICHIA-COLI CONTAINS A PUTATIVE TYPE-III SECRETION SYSTEM NECESSARY FOR THE EXPORT OF PROTEINS INVOLVED IN ATTACHING AND EFFACING LESION FORMATION

Enteropathogenic Escherichia coli (EPEC) causes a characteristic histo pathology in intestinal epithelial cells called the attaching and effa cing lesion. Although the histopathological lesion is well described t he bacterial factors responsible for it are poorly characterized. We h ave identified four EPEC chromosomal genes whose predicted protein seq uences are similar to components of a recently described secretory pat hway (type III) responsible for exporting proteins lacking a typical s ignal sequence. We have designated the genes sepA, sepB, sepC, and sep D (sep, for secretion off. coli proteins), The predicted Sep polypepti des are similar to the Lcr (low calcium response) and Ysc (yersinia se cretion) proteins of Yersinia species and the Mxi (membrane expression of invasion plasmid antigens) and Spa (surface presentation of antige ns) regions of Shigella flexneri. Culture supernatants of EPEC strain E2348/69 contain several polypeptides ranging in size from 110 kDa to 19 kDa, Proteins of comparable size were recognized by human convalesc ent serum from a volunteer experimentally infected with strain E2348/6 9. A sepB mutant of EPEC secreted only the 110-kDa polypeptide and was defective in the formation of attaching and effacing lesions and prot ein-tyrosine phosphorylation in tissue culture cells. These phenotypes mere restored upon complementation with a plasmid carrying an intact sepB gene. These data suggest that the EPEC Sep proteins are component s of a type III secretory apparatus necessary for the export of virule nce determinants.