We are studying the genetic organization of polyoma virus and the virus-coded proteins involved in cell transformation. Polyoma codes for three T-antigens in the early region of its genome. The molecular weights of these proteins are roughly 90K, 60K and 22K daltons. We are analyzing the tryptic peptides of the 60K T-antigen to obtain a precise location for its coding region in the viral DNA. We plan to clone portions of the polyoma genome in bacterial plasmids to study the viral DNA and the 22K T-antigen. We will correlate the organization of viral genomes in transformed cells with control of T-antigen expression and expression of transformation.