Figure 2.

In vitro MPF and CKII phosphorylation. Left, Coomassie-stained gel showing His-tagged DmNopp140-RGG that was expressed in E. coli and purified using nickel affinity columns. Proteolysis was unavoidable. Right, corresponding autoradiogram. Lanes A and A′, protein incubated with MPF and [γ-³²P]-labeled ATP. Lanes B and B′, protein incubated with CKII and γ-labeled ATP. Lanes C and C′, purified protein incubated with γ-labeled ATP, but no enzyme. The same amount of protein was used in each assay. CKII phosphorylation greatly exceeds MPF phosphorylation, probably due to the greater number of CKII sites versus MPF sites. Excess phosphorylation by CKII resulted in a detectable shift in molecular weight (arrow).