In vitro kinase assay for human GST–B-myb (full length) and murine GST–B-myb (aa 225-705).

GST fusion proteins were phosphorylated in vitro by cyclin A1 and cdk2 expressed in Sf9 lysates using ³²P-ATP. Neither cyclin A1 nor cdk2 alone phosphorylated B-myb, but the combination of both led to strong phosphorylation of the murine as well as the human B-myb.