Organization of T Antigens in the Polyoma Virus Genome

The early region of the polyoma virus genome encodes proteins required for cell transformation. The proteins encoded in this region can be identified by immunoprecipitation of infected-cell extracts, using serum from tumor-bearing animals. The proteins identified in this way are called T antigens. At least three T antigens are encoded in the polyoma virus genome (Ito et al. 1977a; Hutchinson et al. 1978; Schaffhausen et al. 1978). These three T antigens, referred to as large, middle, and small T antigens, have apparent molecular weights of 90,000–100,000, 50,000–90,000, and 22,000, respectively, by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis.