Figure 5.

The Thr233 residue of Xrcc4 is phosphorylated by CK2. (A) The T233 and T233P peptides were used in CK2 protein kinase assays. The histogram values represent the corrected means of at least two independent experiments done in duplicate or quadruplicate and the error bars represent standard deviations. (B) Coomassie Blue staining of His-tagged Xrcc4^WT or Xrcc4^T233A proteins used in the kinase assay in (C). (C) An amount of 1 μg of each recombinant protein shown in (B) was used in CK2 kinase assays. A typical experiment is shown. An autoradiograph is shown in the upper panel and normalized, relative phosphorylation values were determined using NIH image software. Input protein was assessed by GelCode staining. (D) Recombinant Xrcc4^250Δ and Xrcc4^250ΔT233A proteins phosphorylated (+) or not (−) by CK2 were incubated with PNK^FHA in PD assays (top panel). Input from the kinase reactions was also assessed by anti-Xrcc4 immunoblotting (bottom panel).