FIG. 7.

Immunoprecipitation of cdk activity with the P2 antibody. (a) Nuclear extracts were prepared from mock-infected MDBK cells (lanes A to D) or at 36 hpi (lanes E to H). Nuclear extracts (100 μg of protein) were immunoprecipitated with IgG from preimmune rabbit sera (lanes A, B, E, and F) or with IgG from P2 antiserum (lanes C, D, G, and H). After immunoprecipitates were washed, [γ-³²P]ATP (10 μCi) and 1.5 μg of GST-Rb (B, D, F, and H) or 1.5 μg of GST fusion protein (A, C, E, and G) was added to the immunoprecipitate. (b) U2-OS cells were transfected with LRTΔSphI (lanes A and B) or LRT (lanes C and D). Nuclear extracts (100 μg of protein) were immunoprecipitated with IgG from P2 antiserum. After immunoprecipitates were washed, [γ-³²P]ATP (10 μCi) and 1.5 μg of GST (A or C) or GST-Rb (B or D) was added to the immunoprecipitate. All protein kinase reactions were carried out as described in Materials and Methods.