Objective:To find cellular proteins that associate with EBNA-3 (also called EBNA-3A), one of the Epstein-Barr virus (EBV)-encoded growth transformation-associated nuclear proteins.Methods:Screening human cDNA libraries in the yeast two-hybrid system and performing an analysis of interaction in vitro as well as in cell lysates.Results:EBNA-3 binds to the epsilon subunit of the chaperonin containing T-complex protein 1 (ε-TCP-1) in the yeast two-hybrid system. The cDNA clone isolated from a human lymphocyte library was found to encode the middle and Cterminal part of ε-TCP-1. The interaction was confirmed by showing that a GST fusion protein specifically precipitated EBNA-3 from CV1 cells infected with recombinant vaccinia virus expressing EBNA-3. The interacting region was mapped to the putative apical domain of ε-TCP-1.Conclusions:This study shows that large, virus-encoded transforming proteins such as EBNA-3 may receive help for their initial folding by chaperonin complexes. The recognition of the chaperonin complex likely occurs through specific interaction with one of the subunits. We suggest that nascent EBNA-3 may recognize the TCP-1 complex by interacting with the apical region of the epsilon subunit.Journal of Human Virology 1999;2:33-37 © Lippincott Williams & Wilkins, Inc.