An immunochemical investigation of SV40 T-antigens 2. Quantitation of antigens and antibody activities

The interaction of the two major forms of simian virus 40 (SV40) T-antigen, large-T and small-t, with antisera has been studied using immunoprecipitation followed by adsorption on to fixed Staphylococcus aureus Cowan 1. With sera derived from hamster bearing bearing tumors of SV40-transformed cells, the amounts of serum required for optimum precipitation of the two antigens were markedly different. Small-t required 15 to 30 times more serum than large-T. This effect can lead to underestimation of small-t or even failure to detect this species. The amount of small-t synthesized in SV40-infected CV-1 cells at late times after infection is substantial, more than equimolar with respect to large-T. Specific antiserum against the large-T polypeptide also precipitates small-t and the two antigens are immunoprecipitated coordinately, consistent with their sharing antigenic determinants. The only antiserum tested which failed to react with small-t was anti-U serum. Even in a sensitive radioimmunoassay, using the denatured polypeptide purified by gel electrophoresis as probe, anti-U serum had no detectable activity against small-t. Coordinate precipitation of large-T and a 53,000-dalton protein from extracts of SV40-transformed mouse cells did not appear to be due to their having shared antigenic determinants, but rather to the existence of a complex of large-T with the 53K protein. The latter protein appears to be a host protein, unrelated to large-T but complexed with it.