Arabidopsis GF14w was originally described because of its apparent association with a DNA-protein complex; it is a member of the 14-3-3 kinase regulatory protein family that is conserved throughout eukaryotes. Here, we demonstrated that recombinant GF14o isexpressed in Escherichia colias a dimer. Blot binding and electrophoretic mobility shift analyses indicated that GFl4o binds calcium. Equilibrium dialysis further demonstrated that G F l h binds an equimolar amount of calcium with an apparent

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... binding constant of 5.5 x 104 M-l under physiological conditions. The C-terminal domain, which contains a potential EF hand motif, is responsible for the calcium binding. The C-terminal domain also cross-reacted with the anti-GF14o monoclonal antibody. In addition, GFl4o is phosphorylated by Arabidopsis protein kinase activity at a serine residue(s) in vitro. Therefore, GF14w protein has biochemical properties consistent with potential signaling roles in plants. The presence of a potential EF hand-like motif in the highly conserved C terminus of 14-3-3 proteins together with the calcium-dependent multiple functions attributed to the 14-3-3 proteins indicate that the C terminus EF hand is a common functional element of this family of proteins.