Figure 2. Biochemical purification of Drosophila casein kinase II.

A) Purification strategy for endogenous casein kinase II. B) Protein composition of peak fraction of activity from the final heparin column visualized by SDS-PAGE and silver-staining. Species identified as casein kinase II alpha and beta are labeled. Bands labeled with an asterisk correspond to contaminating keratin. C) In vitro kinase assay of PSI mutant proteins. Serine to alanine PSI mutant proteins were phosphorylated in vitro using the peak fraction of activity from the final heparin column and using purified recombinant human casein kinase II (NEB P6010S). Assays were visualized using autoradiography, and, to ensure equal protein loading, coomassie staining.