THE ESPB PROTEIN OF ENTEROPATHOGENIC ESCHERICHIA-COLI IS TARGETED TO THE CYTOPLASM OF INFECTED HELA-CELLS

The EspB protein of enteropathogenic Escherichia coli (EPEC) is export ed via a type III secretion apparatus. EspB is critical for signaling the host cell and for the development of the attaching and effacing le sion characteristic of EPEC infection. We used cellular fractionation and confocal laser scanning microscopy to determine the cellular locat ion of EspB during infection of HeLa cells. Both methods indicated tha t EspB is targeted to the cytoplasm of infected cells. Using mutants, we found that EspB targeting to the host cell cytoplasm requires the t ype III secretion apparatus and the secreted proteins EspA and EspD, b ut not intimin. These results provide insights into the function of th e type III secretion apparatus of EPEC and the functions of the Esp pr oteins.