Figure 5. PLK1 phosphorylates 4E-BP1 in vitro. A recombinant GST, GST fused full-length and truncated 4E-BP1 were incubated with a commercial purified PLK1 protein in the presence of [³²P]-γ-ATP in the kinase reaction buffer. Proteins were analyzed by SDS–PAGE and visualized by autoradiography (kinase assay) or Coomassie blue staining (staining). Casein was used as positive control.