FIG. 3.

Irradiated 32D cells arrested in G₁ have inactive cyclin E-Cdk2 complexes but retain active Cdk4 and Cdk7. Cell lysates from the 32D-EpoR[H] cultures represented in Fig. 1B were immunoprecipitated (I.P.) with antibodies to Cdk4, Cdk2, cyclin E, or Cdk7, and in vitro kinase assays were performed (Activity). Immunoprecipitated proteins were Western blotted with Cdk4 antibodies (Cdk4 IP), total and phosphorylation site-specific Cdk2 antibodies (Cdk2 and cyclin E IPs), or Mat1 antibodies (I.P. Cdk7).