MINIREVIEW Common and Unique Features of T Antigens Encoded by the Polyomavirus Group

Simian virus 40 (SV40) and murine polyomavirus (PyV) have proved to be powerful models for understanding the molecular events involved in the regulation of eukaryotic genome expression and replication. In addition, the fact that these viruses are tumorigenic in animals and transform cells in culture has provided investigators with tools with which to dissect the mechanisms leading to tumorigenicity. Much of the progress made with these systems is due to their ele-gantly simple genome structure and strategy of productive infection. After infection, transcription initiating at the early promoter leads to synthesis of the early viral genes. SV40 encodes two early proteins, large T antigen and small t antigen, while PyV expresses three, the large, small, and middle T antigens. The action of one or more of these proteins results in replication of the viral genome, activatio