An N-terminal transformation-governing sequence of SV40 large T antigen contributes to the binding of both p110Rb and a second cellular protein, p120.

In addition to Rb and p53, a third cellular protein, p120 in monkey and p118 in human cells, forms a specific complex with SV40 large T antigen (T). p118/120 is not a product of the Rb-gene. As was shown with T/Rb complex formation, the interaction between T and p120 is dependent on the intact nature of a ten residue, transformation-controlling domain in T (residues 105-114). In mouse cells, a readily detectable protein of 115 kd was detected, which, like murine Rb, also forms a stable complex with T. Like p118/120, p115 binding is also dependent on the intact nature of the 105-114 sequence. Given their similar size and T antigen binding sequence dependence, p115 and p118/120 may be products of the same gene in different species. These results suggest that interactions between T and p115/118/120, as well as T and Rb, contribute to the SV40 transforming mechanism.