SV40: T antigen, the A function and transformation

T antigen, a protein found in the nuclei of SV40-transformed and -infected cells, can be purified and characterized. Our data suggest that T antigen in transformed cells is found at least in part in a large 22S complex, suggesting that this 22S form may contain T antigen complexed with other viral or host proteins. We prefer the assumption that T antigen is correlated with the A function, although a definitive in vitro proof for this hypothesis is still missing. Mutants in the A function most likely interfere with the maintenance of transformation, a result inviting the interpretation that the A function may indeed govern DNA synthesis of the transformed cell or influence the cell's ability to pass from G1 (or G0) to S. Thus transformation by SV40 may be a direct consequence of the introduction of the SV40 replicon and the presence of its initiator function which is used by the transformed cell.