FIG. 7.

Phosphorylation of PAP by cyclin B₁-cdc2 is CRM enhanced. (A) Lower concentrations of CRM stimulate cyclin B₁-cdc2 phosphorylation of PAP. Purified PAP and cyclin B₁-cdc2 were incubated under kinase conditions in the presence of [γ-³²P]ATP and increasing concentrations (4.3, 5.2, 6.1, 7, 7.8, and 8.7 μM) of either PAP's CRM (lanes 2 to 7) or an 8-mer peptide of scrambled sequence (lanes 8 to 12) or else they were incubated with no peptide (lane 1). Phosphorylated proteins were resolved by SDS-PAGE and detected by autoradiography. An arrow on the left indicates the position of PAP. (B) Equivalent concentrations of CRM have either no effect or an inhibitory effect on pRB's phosphorylation by cyclin B₁-cdc2. Kinase reactions were carried out as described above. Lanes 2 to 7 contained increasing amounts (4.3, 5.2, 6.1, 7, 7.8, and 8.7 μM) of PAP's CRM, and lanes 8 to 11 contained increasing amounts (4.3, 6.1, 7.8, and 8.7 μM) of the scrambled sequence peptide. An arrow on the left indicates the position of pRB. (C) No CRM peptide effect is observed on phosphorylation of histone H1 by cyclin B₁-cdc2. As above, the same concentrations of either the CRM 8mer (lanes 2 to 7) or the scrambled sequence 8-mer (lanes 8 to 12) were added to the kinase assays. An arrow on the left indicates the position of histone H1.