CDC25 enzymes are dual-specificity phosphatases involved in the regulation of the cell cycle. No CDC25 enzymes have been described in higher plant organisms. We report here the characterization of an Arabidopsis thaliana CDC25 enzyme, constituted by a sole catalytic domain and devoid of the N-terminal regulatory region found in the human CDC25. We describe the recombinant expression in Escherichia coli of the Arath;CDC25 and its purification for activity assay and structure determination by NMR. The recombinant enzyme has a tyrosine phosphatase activity towards an artificial substrate, a NMR characterization equally concludes to its correct folding. The secondary structure of the protein was predicted on the basis of the assigned chemical shift of H-1, N-15, and C-13 backbone atoms of the protein. The presence of a metal ion in the C-terminus of this new protein points to a zinc finger, and sequence homology indicates that this new structural element might be conserved in related plant homologs. (C) 2004 Elsevier Inc. All rights reserved.