Yeast -encoded Phosphatidate Phosphatase Controls the Expression of -encoded Phosphatidylserine Synthase for Membrane Phospholipid Synthesis

The -encoded phosphatidate phosphatase (PAP), which catalyzes the committed step for the synthesis of triacylglycerol in , exerts a negative regulatory effect on the level of phosphatidate used for the synthesis of membrane phospholipids. This raises the question whether PAP thereby affects the expression and activity of enzymes involved in phospholipid synthesis. Here, we examined the PAP-mediated regulation of -encoded phosphatidylserine synthase (PSS), which catalyzes the committed step for the synthesis of major phospholipids via the CDP-diacylglycerol pathway. The lack of PAP in the Δ mutant highly elevated PSS activity, exhibiting a growth-dependent up-regulation from the exponential to the stationary phase of growth. Immunoblot analysis showed that the elevation of PSS activity results from an increase in the level of the enzyme encoded by Truncation analysis and site-directed mutagenesis of the promoter indicated that Cho1 expression in the Δ mutant is induced through the inositol-sensitive upstream activation sequence (UAS), a -acting element for the phosphatidate-controlled Henry (Ino2-Ino4/Opi1) regulatory circuit. The abrogation of Cho1 induction and PSS activity by a UAS mutation suppressed Δ effects on lipid synthesis, nuclear/endoplasmic reticulum membrane morphology, and lipid droplet formation, but not on growth at elevated temperature. Loss of the -encoded diacylglycerol kinase, which converts diacylglycerol to phosphatidate, partially suppressed the Δ-mediated induction of Cho1 and PSS activity. Collectively, these data showed that PAP activity controls the expression of PSS for membrane phospholipid synthesis.