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Molecular Characterization of a Tyrosine-Specific Protein Phosphatase Encoded by a Stress-Responsive Gene in Arabidopsis

Qiang Xu, Hui-Hua Fu, Rajeev Gupta and Sheng Luan
The Plant Cell
Vol. 10, No. 5 (May, 1998), pp. 849-857
DOI: 10.2307/3870670
Stable URL: http://www.jstor.org/stable/3870670
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Molecular Characterization of a Tyrosine-Specific Protein Phosphatase Encoded by a Stress-Responsive Gene in Arabidopsis
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Abstract

Protein tyrosine kinases and phosphatases play a vital role in the regulation of cell growth and differentiation in animal systems. However, none of these enzymes has been characterized from higher plants. In this study, we isolated a cDNA encoding a putative protein tyrosine phosphatase (PTPase) from Arabidopsis (referred to as AtPTP1). The expression level of AtPTP1 is highly sensitive to environmental stresses. High-salt conditions increased AtPTP1 mRNA levels, whereas cold treatment rapidly eliminated the AtPTP1 transcript. The recombinant AtPTP1 protein specifically hydrolyzed phosphotyrosine, but not phosphoserine/threonine, in protein substrates. Site-directed mutagenesis defined two highly conserved amino acids, cysteine-265 and aspartate-234, as being essential for the phosphatase activity of the AtPTP1 protein, suggesting a common catalytic mechanism for PTPases from all eukaryotic systems. In summary, we have identified AtPTP1 as a tyrosine-specific protein phosphatase that may function in stress responses of higher plants.

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