Figure 4. CK2α-binding activity of CK2β mutant proteins.

(A) Solid-phase CK2α-binding assay of different CK2β mutants. Immobilized wild-type (WT) CK2β was incubated with [³⁵S]methionine-labelled CK2α in the presence of increasing concentrations of soluble wild-type MBP–CK2β or MBP–CK2β mutants as indicated. After washing, the amount of associated CK2α was evaluated by radioactivity counting. Results are the means±S.D. (n=3). (B) Real-time binding kinetics between immobilized GST–CK2α and different MBP–CK2β mutant proteins measured by surface plasmon resonance. The interaction between immobilized GST–CK2α and MBP–CK2β mutants was recorded as described in the Experimental section. RU, response units.