Comparison of T Antigen-associated Host Phosphoproteins from SV40-infected and -transformed Cells of Different Species

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Abstract
SV40-infected and -transformed cells contain, in addition to the virus-coded tumor antigens, 1 or more 48-56 K (kilodaltons) host tumor antigens. At least part of this class of host proteins exists as a fast-sedimenting complex with the SV40 large T antigen. The host proteins associated with the large T antigen in SV40-transformed monkey, mouse and human cells and SV40-infected monkey cells were compared by 2-dimensional gel electrophoresis and V8 partial proteolysis peptide mapping. Although these proteins differed slightly in apparent MW and peptide pattern, they migrated identically in isoelectric focusing gels. The cellular proteins associated with large T antigen in different hosts are very closely related to each other. Despite their similarities, the 55 K proteins from different host cells form complexes of different stabilities with large T antigen, as judged by spontaneous dissociation of the complexes during storage, and the fractions of the 55 K cellular protein and large T antigen found free and in the complexed form in each different host cell.