PP7, A PLANT PHOSPHATASE REPRESENTING A NOVEL EVOLUTIONARY BRANCH OF EUKARYOTIC PROTEIN SER THR PHOSPHATASES/

We describe a novel protein Ser/Thr phosphatase from Arabidopsis thali ana, PP7, which is only 27-32% identical in amino acid sequence to the known phosphatases and is the most divergent member of the PPP (PP1/2 A/2B) family for today. Some structural features suggest more close re lationship of PP7 to the PP5/rdgC subfamily. PP7 contains all of the r esidues essential for the phosphatase activity and possesses three maj or insertions in its presumable C-terminal subdomain, which suggest it s unique regulation and/or optimisation of its structure for interacti on with specific substrates or regulators. A phosphatase structurally related to PP7 is expressed in rice. PP7 conservation between mono- an d dicotyledonous plants may point to its essential role in the plant c ell.