Identification of new polypeptide species (48–55K) immunoprecipitable by antiserum to purified large T antigen and present in SV40-infected and -transformed cells

Abstract

New polypeptide species with molecular weights between 48K and 55K can be immunoprecipitated with serum against purified 94K T antigen (T Ag) of SV40 as well as with antitumor serum. These related species have been separated by SDS-polyacrylamide gel electrophoresis into a spectrum with predominating bands characteristic of each cell line examined. The SV40-infected cell lines examined are the following: SV40-infected TC-7 and Vero cells, and the SV40-transformed lines SV3T3, VLM, SV28, and SV80. The 48K–55K species have not been observed in the immunoprecipitates of uninfected cell extracts. The purified 48K species, excised from gels, can be specifically reimmunoprecipitated with the anti-94K T Ag serum. The possibility that the 48K–55K species may be in vitro proteolytic products of the 94K T Ag has been excluded by a variety of experiments involving the use of mixed extracts, the use of inhibitors of proteolysis, and comparison of their methionine-containing tryptic peptides. Deletion mutants of SV40 mapping between 0.54 and 0.59 map units do not affect the appearance or size of these new species. The SV40 mutant tsA58 produces a 55K species which is very stable at high and low temperatures, suggesting that the mutation does not affect the new antigen. The results suggest that the 48K–55K species may originate either as host-coded species (perhaps induced by the virus) that share determinants with T Ag or perhaps as SV40-encoded species sharing only very little of the amino acid sequence of 94K T Ag.