Figure 1.

Peptide inhibition of cyclin/cdk2. (A) Phosphorylation of GST-RB in vitro by control (lane 1), anti-cyclin A (lanes 2–7), or anti-cyclin B (lanes 8–13) immunoprecipitates in the presence of γ-³²P-ATP. Where indicated, TAT-LDL (final concentration 0.1, 1, and 10 μM as indicated by the triangles), TAT-Umt (10 μM), or TAT (10 μM) peptides were added before the addition of substrate. (B) Asynchronously growing U2OS osteosarcoma cells were treated with the indicated peptides (50 μM) for 4 hr, lysed, and immunoprecipitated with anti-cdk2 (lanes 1–5) or a control antibody (lane 6). In vitro kinase reactions were performed in the presence of γ-³²P-ATP using GST-RB as substrate and resolved by SDS/PAGE. Phosphorylation of GST-pRB and recovery of cdk2 were monitored by autoradiography and anti-cdk2 immunoblot analysis, respectively.