Shiga toxin-producing Escherichia coli (STEC), enteropathogenic E. coli (EPEC) and some strains of Hafnia alvei are capable of inducing attaching and effacing (A/E) lesions, characterized by tight apposition of the bacteria to the eukaryotic membrane and formation of actin-based pedestals. In this study, we report on the identification of EspE, a novel secreted 80 kDa protein of A/E bacteria. During infection, EspE is delivered into the cytoplasm of the infected host cell, where it is detected as a higher-molecular-weight form of 90 kDa. We present evidence that translocated EspE becomes tyrosine phosphorylated and that this modified form of EspE may be identical to Hp90, the putative receptor of EPEC intimin. Bacteria of the classic enterohaemorrhagic E. coli (EHEC) serotype O157:H7 fail to induce a tyrosine phosphorylation of EspE and differ in this respect from other A/E bacteria. Translocated EspE, whether tyrosine phosphorylated or not, becomes incorporated into the bacteria-induced cytoskeletal structures, where it normally colocalizes with filamentous actin. EPEC are also able to induce 'pseudopods', elongated pedestals that have recently been implicated in a novel kind of actin-based motility. EspE is enriched at the tip of these structures, suggesting its involvement in the process of actin dynamics, which is triggered during the attaching and effacing process.