Fig. 4.

Thr-401 is the major _XJTGB1 protein site for CK2 phosphorylation. (A) LC-MS/MS analysis of _XJTGB1 protein phosphorylation by NbCK2α. The absence of phosphoric acid (97.9769Da) on the y₁₆ ion fragment demonstrates that Thr-401 is a phosphorylation site for CK2 kinase. (B) Identification of the phosphorylation sites in _XJTGB1 protein mutants by in vitro phosphorylation with HvCK2α and NbCK2α. The radioactive intensities of the _XJTGB1 protein and its phosphorylation mutants indicate the extent of radiolabelling with [γ-³²P]ATP. CBB-stained proteins at the bottom of the panels (B) and (C) are as indicated in Fig. 2B. (C) Phosphorylation comparisons of selected _XJTGB1 protein mutants with wt _XJTGB1 protein to confirm that Thr-401 is the major phosphorylated residue. (This figure is available in colour at JXB online.)