The invasin protein of the pathogenic Yersinia pseudotuberculosis mediates entry of the bacterium into cultured mammalian cells by binding several beta 1 chain integrins. In this study, we identified the region of invasin responsible for cell recognition. Thirty-two monoclonal antibodies directed against invasin were isolated, and of those, six blocked cell attachment to invasin. These six antibodies recognized epitopes within the last 192 amino acids of invasin. Deletion mutants of invasin and maltose-binding protein (MBP)--invasin fusion proteins were generated and tested for cell attachment. All of the invasin derivatives that carried the carboxyl-terminal 192 amino acids retained cell binding activity. One carboxyl-terminal invasin fragment and seven MBP--invasin fusion proteins were purified. The purified derivatives that retained binding activity inhibited bacterial entry into cultured mammalian cells. These results indicated that the carboxyl-terminal 192 amino acids of invasin contains the integrin-binding domain, even though this region does not contain the tripeptide sequence Arg-Gly-Asp.