The goal of this project is to elucidate and characterize biological properties of SV40 early proteins. The antigenic relatedness of SV40 large T, small t, U, and S antigens was established using antiserum directed against purified, denatured T polypeptide. The presence of large T-ag in the plasma membrane of SV40-infected and transformed cells was established. Transport-defective mutants of SV40-adenovirus 7 hybrid virus (PARA) were found to exhibit a dominant effect which inhibited nuclear migration of wild-type SV40 T-ag.