Figure 4.

Phosphorylation of GAIP by purified CK2. (A) GST-furin cd (1 μg), His6 GAIP, or His6 GAIP (S24A) (5 μg each) were incubated for 1 h at 30°C in the presence (+) or in the absence (−) of purified CK2, [γ-³²P], and 2 mM MgCl₂. Both wild-type GAIP and GAIP (S24A) are phosphorylated by recombinant CK2 (arrow), but phosphorylation of the mutant GAIP is reduced. (B) Equal amounts (5 μg) of GAIP and GAIP (S24A) were incubated with CK2 and processed as in A. Bands corresponding to phosphorylated GAIP were excised, and the amount of [³²P] incorporation was determined by scintillation counting. Phosphorylation of GAIP (S24A) is reduced by 50% compared with wild-type GAIP.