FIG. 4.

The binding of p300 to cyclin E-Cdk2 requires cyclin E-Cdk2 from a cellular source. (A) GST-p300 binds Cdk2 from nuclear extracts. GST (lane 2) or GST-p300 (lane 3) was incubated with nuclear extracts from Jurkat T lymphocytes. Protein complexes were analyzed by SDS–12% PAGE followed by Western blotting using antibodies to Cdk2. Lane 1 contains 10% of the input nuclear extract. (B) Cdk2 and p300 coimmunoprecipitate in nuclear extracts. Immunoprecipitations were performed on Jurkat cell nuclear extracts with control antibodies (lane 4) or antibodies to p300 (lane 5). Protein complexes were analyzed by SDS–8% PAGE, followed by Western blotting with antibodies to Cdk2. (C) Cdk2, cyclin E, and p300 coimmunoprecipitate in nuclear extracts. Jurkat cell nuclear extracts were immunoprecipitated with antibodies to Cdk2. Protein complexes were resolved by SDS-PAGE, followed by Western blotting with antibodies to p300 (lane 6), cyclin E (lane 7), or Cdk2 (lane 8). Ab, antibody.