Plant Physiol. EPICENTRE Biotechnologies
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Uridine 5'-Monophosphate Synthase Is Transcriptionally Regulated by Pyrimidine Levels in Nicotiana plumbaginifolia1

Djoko Santoso2 and Robert Thornburg*

Department of Biochemistry and Biophysics, Iowa State University, Ames, Iowa 50011

To understand the regulation and expression of pyrimidine biosynthesis in plants, we have examined the effect of the metabolic inhibitor 5-fluoroorotic acid (FOA) on uridine-5'-monophosphate synthase (UMPSase) expression in cell cultures of Nicotiana plumbaginifolia. UMPSase is the rate-limiting step of pyrimidine biosynthesis in plants. Addition of FOA causes an up-regulation of UMPSase enzyme activity in cell cultures after a lag phase of several days. Western-blot analysis demonstrated that the up-regulation in enzyme activity was caused by increased expression of the UMPSase protein. Northern-blot analysis demonstrated a higher level of UMPSase mRNA in the FOA-induced tissues than in control tissues. Run-on transcriptional assays showed that the UMPSase gene was transcriptionally activated after FOA treatment. The mechanism of toxicity of FOA is through thymine starvation. We found that addition of thymine abrogated the FOA-mediated up-regulation of UMPSase. In addition, methotrexate and aminopterin, which affect thymine levels by inhibiting dihydrofolate reductase, also up-regulate UMPSase in N. plumbaginifolia cells.

1   This work was sponsored by grant no. 91-37301-6208 from the U.S. Department of Agriculture. This is journal paper no. J-16512 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA.
2   Present address: Biotechnology Research Unit for Estate Crops, Bogor, Indonesia.
*   Corresponding author; e-mail thorn{at}iastate.edu; fax 1-515-294-0453.

Plant Physiol. (1998) 116: 815-821
Copyright Clearance Center:   0032-0889/98/116/0815/07
© 1998 American Society of Plant Physiologists




This article has been cited by other articles:


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D. Santoso and R. Thornburg
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Copyright © 1998 by the American Society of Plant Biologists