Figure 1.

Changes in cell-cycle regulatory proteins during erythroleukemia cell differentiation. MEL cells were treated with 5 mM HMBA for the indicated times, and total cellular-protein extracts were prepared and analyzed for specific CDK activities by immunoprecipitation-kinase assays (A) or CDK protein levels were analyzed by immunoblotting (B) as described in Materials and Methods. BP = Blocking peptides. (C) MEL cells were treated with 5 mM HMBA for the indicated times, and nuclear and cytoplasmic protein extracts were prepared and analyzed for specific CDK activities as described in Materials and Methods. (D) CDKI protein levels were analyzed by immunoblotting as described in Materials and Methods.