Two-hybrid system was applied to screen proteins interacting with IpaC in the host cell. By using two-hybrid system, the bait plasmid containing ipaC gene was constructed and designated pGBKT-IpaC. A human HeLa cDNA library was screened to isolate protein factors that might interact with IpaC. Among the 2 x 10(6) clones screened, 22 positive clones were picked out. Sequence analysis revealed that two of them contained cDNA fragments from collagenase. Subsequently the domain of IpaC interacting with collagenase fragment was identified. These results suggest that IpaC might play a role in some biological processes where collagenase is involved.