Simian virus 40 large T antigen stably complexes with a 185-kilodalton host protein

Stable interactions between simian virus 40 large T antigen and host proteins are believed to play a major role in the ability of the viral protein to transform cells in culture and induce tumors in vivo. Two of these host proteins, the retinoblastoma susceptibility protein (pRB) and p53, are products of tumor suppressor genes, suggesting that T antigen exerts at least a portion of its transforming activity by complexing with and inactivating the function of these proteins. While analyzing T antigen-host protein complexes in mouse cells, we noted a protein of 185 kDa (p185) which specifically coimmunoprecipitates with T antigen. Coimmunoprecipitation results from the formation of stable complexes between T antigen and p185. Complex formation is independent of the interactions of T antigen with pRB, p120, and p53. Furthermore, analysis of T-antigen mutants suggests that T antigen-p185 complex formation may be important in transformation by simian virus 40.