Fig. 2. CKII phosphorylates the N-terminus of ß-catenin. (A) ß-catenin wt and deletion constructs expressed as GST-fusion proteins and tested in kinase assays in vitro. (B) The proteins were subjected to kinase assays as described in Fig. 1A, but with or without heparin (5 µg/µl) as an inhibitor of CKII-activity. Phosphorylation is efficiently reduced by heparin at the N-terminus (aa 1-119, 1-302) but not at the C-terminus of ß-catenin. In the control-lane (co), unrelated mouse IgG in the initial immunoprecipitation was used and incubated with full-length GST ß-catenin. The Coomassie-stain provides the loading control for the respective fusion-proteins. (C) Three conserved CKII consensus motifs can be found in the N-terminus of ß-catenin (aa 1-119). These sites are located in close proximity to the GSK-3ß consensus motif (Aberle et al., 1997). No additional CKII sites are located in the extended N-terminal region (aa 120-302) of ß-catenin (not shown).