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J. Biol. Chem., Vol. 282, Issue 43, 31217-31227, October 26, 2007

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Respiratory Deficiency Mediates the Regulation of CHO1-encoded Phosphatidylserine Synthase by mRNA Stability in Saccharomyces cerevisiae^*

From the Department of Food Science and Rutgers Center for Lipid Research, Rutgers University, New Brunswick, New Jersey 08901

The CHO1-encoded phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) is one of the most highly regulated phospholipid biosynthetic enzymes in the yeast Saccharomyces cerevisiae. CHO1 expression is regulated by nutrient availability through a regulatory circuit involving a UAS_INO cis-acting element in the CHO1 promoter, the positive transcription factors Ino2p and Ino4p, and the transcriptional repressor Opi1p. In this work, we examined the post-transcriptional regulation of CHO1 by mRNA stability. CHO1 mRNA was stabilized in mutants defective in deadenylation (ccr4), mRNA decapping (dcp1), and the 5'–3'-exonuclease (xrn1), indicating that the CHO1 transcript is primarily degraded through the general 5'–3' mRNA decay pathway. In respiratory-sufficient cells, the CHO1 transcript was moderately stable with a half-life of 12 min. However, the CHO1 transcript was stabilized to a half-life of >45 min in respiratory-deficient (rho^– and rho^o) cells, the cox4 mutant defective in the cytochrome c oxidase, and wild type cells treated with KCN (a cytochrome c oxidase inhibitor). The increased CHO1 mRNA stability in response to respiratory deficiency caused increases in CHO1 mRNA abundance, phosphatidylserine synthase protein and activity, and the synthesis of phosphatidylserine in vivo. Respiratory deficiency also caused increases in the activities of CDP-diacylglycerol synthase, phosphatidylserine decarboxylase, and the phospholipid methyltransferases. Phosphatidylinositol synthase and choline kinase activities were not affected by respiratory deficiency. This work advances our understanding of phosphatidylserine synthase regulation and underscores the importance of mitochondrial respiration to the regulation of phospholipid synthesis in S. cerevisiae.

Received for publication, June 21, 2007 , and in revised form, August 15, 2007.

^* This work was supported in part by United States Public Health Service Grant GM-50679 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Food Science, Rutgers University, 65 Dudley Rd., New Brunswick, NJ 08901. Tel.: 732-932-9611 (Ext. 217); E-mail: carman{at}aesop.rutgers.edu.

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