Analyses of cell cycle regulatory protein expression and function of kinases. (A) Immunoblots with different antibodies as indicated. Actin was used as loading control. (B-D). CDK6 or cyclin D3 was immunoprecipitated from thymocyte extracts and blotted with the indicated antibodies. HC indicates IgG heavy chain. Lane 1 (WT-Δ) represents input (50 μg). (E-G) In vitro kinase assay (CDK6, CDK4, or CDK2) was immunoprecipitated from thymocyte extracts, and an in vitro kinase assay was performed using the recombinant retinoblastoma protein (GST-RB) as the substrate.