Protein-protein interactions are essential for virtually every cellular process. A fundamental question in the study of any protein is determining the identity of proteins it interacts with. We propose to develop an avian two hybrid system which utilizes avian replication competent retroviruses to discover protein-protein interaction. PROPOSED COMMERCIAL APPLICATION: Success will lean to the marketing of vectors and stable avian cell lines for two-hybrid library screenings. There exists a substantial market for the yeast two hybrid systems.