REGULATION OF YEAST PHOSPHOLIPID BIOSYNTHETIC GENE IN PHOSPHATIDYLSERINE DECARBOXYLASE MUTANTS

In the yeast Saccharomyces cerevisiae, the products of two genes (PSD1 and PSD2) are able to catalyze the decarboxylation of phosphatidylser ine (PS) to produce phosphatidylethanolamine (PE) (C, J, Clancey, S, C hang, and W, Dowhan, J, Biol, Chem, 268:24580-24590, 1993; P, J, Trott er, J, Pedretti, and D, R, Voelker, J, Biol, Chem, 268:21416-21424, 19 93; P, J, Trotter, and D, R, Voelker, J, Biol, Chem, 270:6062-5070, 19 95). I report that the major mitochondrial PS decarboxylase gene (PSDI ) is transcriptionaly regulated by inositol in a manner similar to tha t reported for other coregulated phospholipid biosynthetic genes, The second PS decarboxylase gene (PSD2) is not regulated on a transcriptio nal level by inositol and/or ethanolamine. In yeast, phosphatidylcholi ne (PC) biosynthesis is required for the repression of the phospholipi d biosynthetic genes, including the INO1 gene, in response to inositol . I show that the presence of a functional major mitochondrial PS deca rboxylase encoded by the PSDI gene is necessary for proper regulation of IN01 in response to inositol in the absence of ethanolamine, Disrup tion of the second PS decarboxylase gene (PSD2) does not affect the IN 01 regulation. Analysis of phospholipid content of PS decarboxylase mu tants suggests that the proportion of PC on total cellular phospholipi ds is not correlated to the cell's ability to repress IN01 in response to inositol, Rather, yeast cells are apparently able to monitor the f lux through the phospholipid biosynthetic pathway and modify the trans cription of phospholipid biosynthetic genes accordingly.