FIG. 8.

Phosphorylation of PAP by cdks is CRM dependent. (A) Higher concentrations of CRM specifically inhibit cyclin B₁-cdc2 phosphorylation of PAP. Kinase reactions were carried out as described in Fig. 7. Samples in lanes 1 to 5 contained increasing amounts of CRM peptide (0, 5.8, 11.6, 17.3, and 22.5 μM). Arrows to the left indicate the positions of PAP and cyclin B₁. (B) Phosphorylation of PAP by cyclin A-cdk2 is CRM dependent. Inhibition of cdk activity toward PAP by either by PAP's CRM or p21's CRM was tested. Purified PAP and cyclin A-cdk2 were incubated under kinase conditions in the presence of [γ-³²P]ATP (lane 1). Kinase reactions contained 23 μM concentrations of either PAP's CRM (lane 2), p21's CRM (lane 3), or no peptide (lane 1). Arrows to the left indicate the positions of PAP and cyclin A.