Host cell-modified T-antigen in membranes of simian virus 40-transformed hamster cells.

Highly purified plasma membranes of simian virus 40 (SV40)-transformed hamster and mouse cells were subjected to indirect immunoprecipitation and bidimensional isoelectric focusing-immunoelectrophoresis with high-titer (greater than or equal to 512) sera against SV40 T-antigen. An SV40-specific protein of approximately 100,000 daltons and pH-4.7 isoelectric point cross-reacted immunologically with T-antigen, which indicated the presence of a T-antigen species. However, this protein appeared to be host cell modified because of its low isoelectric point and its reactivity with heterologous antisera containing antibodies specific for neuraminidase- and trypsin-sensitive carbohydrate and/or peptide moieties lacking nuclear T-antigen. Another protein specific for the membranes of SV40-transformed cells had a molecular mass near 60,000 daltons and an isoelectric point at pH 4.5 and appeared closely associated with membrane T-antigen. It coprecipitated with membrane T-antigen upon direct immunoprecipitation with anti-T serum. However, when this protein was dissociated from membrane T-antigen by isoelectric focusing in the presence of Triton X-100 and urea, its reactivity with anti-T serum was lost. This suggested that the protein was not encoded in the SV40 genome.