FIGURE 8.

Quantitative phosphorylation of plant initiation factors by CK2. rAteIF2α (250 pmol), rAteIF2β (250 pmol), rAteIF4B1(150 pmol), rAteIF4B2 (150 pmol), and rAteIF5 (250 pmol) and rWheIF2α (250 pmol), rWheIF2β (250 pmol), rWheIF4B (250 pmol), or rWheIF5 (250 pmol) were incubated with CK2 as described under “Experimental Procedures.” Reactions were stopped by the addition of ∼1 ml of cold HMK buffer. Samples were immediately captured on a nitrocellulose filter and quantitated using a scintillation counter. Each reaction was performed in triplicate, and the results were averaged. Error bars represent standard deviation. CK2α1 was used to phosphorylate rWheIF2α, rAteIF5, rWheIF5, and rWheIF4B. CK2α1β4 was used to phosphorylate AtreIF2β, rWheIF2β, rAteIF4B1, and rAteIF4B. Because CK2β4 undergoes autophosphorylation, a separate blank was run for this reaction. Note that scales for the y axis vary.