Small-t and large-T antigens cooperate to drive cell proliferation.

Optimal transformation efficiencies or tumour formation in certain target tissues require the SV40 small-t antigen in addition to the transforming protein, large-T. We have used two model systems in which small-t is required for transformation to roles of individual viral proteins in this process. These systems include anchorage-independent growth of rat fibroblasts and focus formation by primary human diploid fibroblasts. In both cases, large-T and small-t antigens work together to drive cell cycle induction. Thus, the need for both tumour antigens is apparent in the initial step of the transformation process, the stimulation of quiescent cells to enter the cell cycle.