Polyoma small and middle T antigens and SV40 small t antigen form stable complexes with protein phosphatase 2A

Cell. 1990 Jan 12;60(1):167-76. doi: 10.1016/0092-8674(90)90726-u.


We have purified the 36 and 63 kd cellular proteins known to associate with polyomavirus middle and small tumor (T) antigens and SV40 small t antigen. Microsequencing of the 36 kd protein indicated that it was probably identical to the catalytic subunit of protein phosphatase 2A (PP2A). Identity was confirmed by comigration on two-dimensional (2D) gels and by 2D analysis of complete chymotryptic digests. In addition, PP2A-like phosphatase activity was detected in immunoprecipitates of wild-type middle T. Immunoblotting experiments, comigration on 2D gels, and 2D analysis of limit chymotryptic digests demonstrated that the 63 kd protein, present in the middle T complex in approximately equimolar ratio to the 36 kd protein, is a known regulatory subunit of the PP2A holoenzyme. Finally, the 36 kd PP2A catalytic subunit can be immunoprecipitated by anti-pp60c-src antisera only from cells expressing wild-type middle T. These results suggest that complex formation between PP2A and T antigens may be important for T antigen-mediated transformation.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antigens, Polyomavirus Transforming*
  • Binding Sites
  • Cell Line
  • Immunoblotting
  • Macromolecular Substances
  • Mice
  • Molecular Sequence Data
  • Peptide Fragments / isolation & purification
  • Peptide Mapping
  • Phosphoprotein Phosphatases / isolation & purification
  • Phosphoprotein Phosphatases / metabolism*
  • Phosphorylase Phosphatase / metabolism
  • Polyomavirus / immunology*
  • Protein Binding
  • Protein Phosphatase 2
  • Simian virus 40 / immunology*
  • Trypsin


  • Antigens, Polyomavirus Transforming
  • Macromolecular Substances
  • Peptide Fragments
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 2
  • Phosphorylase Phosphatase
  • Trypsin