IDENTIFICATION OF NEW POLYPEPTIDE SPECIES (48-55K) IMMUNOPRECIPITABLE BY ANTISERUM TO PURIFIED LARGE T-ANTIGEN AND PRESENT IN SV40-INFECTED AND SV40-TRANSFORMED CELLS

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. © 1979.