The discovery of tyrosine phosphorylation: It's all in the buffer!

Polyomavirus, discovered by Ludwik Gross as a contaminant in a murine leukemia virus preparation in the early 1950s, was termed polyomavirus by Sarah Stewart and Bernice Eddy because of its ability to elicit multiple different types of tumors in mice. By 1960, culture conditions for growing polyomavirus in vitro had been developed, and its ability to "transform" cells in culture had been established. Because of the ease of propagation and the small size of its double-stranded DNA genome (<5 kb), polyomavirus quickly became one of the favorite model systems for studying the process of carcinogenesis. The hope was that an understanding of how this simple tumor virus transforms cells would shed light on the mechanisms underlying the human disease. The isolation of temperature-sensitive polyomavirus mutants defective in transformation at the restrictive temperature and the identification of viral transcripts in transformed cells suggested that a viral gene product might be responsible for the transformed state. In addition, rodents infected with polyomavirus had been found to develop antibodies against polyomavirus-infected cell-specific antigens, which became known as T (tumor) antigens. Although formal proof that the T antigens are encoded by the polyomavirus genome had to wait several more years, at the time it seemed plausible that these proteins were indeed virally coded and that one or more of them had oncogenic properties. When the work that ultimately led to our paper began in 1977, there was intense interest in the identity of the polyomavirus T antigen proteins and the molecular basis for their ability to transform cells. From the early days, the Saik Institute had been a mecca for the study of polyomavirus because Renato Dulbecco, a founding faculty member of the Institute in 1964, had been one of the pioneers in studying polyomavirus and had trained a cadre of young investigators who went on to study polyomavirus in their own groups--these included Mike Fried who moved to ICRF in London, Tom Benjamin who moved to Harvard Medical School, and Walter Eckhart who stayed at the Salk Institute to set up his own group studying polyomavirus. During 1977 and early 1978, we, together with Mary Anne Hutchinson, had been busy characterizing the polyomavirus T antigens by peptide mapping of immunoprecipitated metabolically labeled proteins, combined with analysis of virus deletion mutants and in vitro translation of virally derived mRNAs and cRNAs. For polyomavirus, three different sized T antigens had been identified by Yoshi Ito and Renato Dulbecco, who had moved to ICRF in 1972 (Ito et al., 1977a, 1977b). These became known rather unimaginatively as large, middle,