Cyclin‐dependent kinase‐mediated phosphorylation of yeast phosphatidate phosphatase

Abstract

The yeast PAH1‐encoded phosphatidate (PA) phosphatase catalyzes the dephosphorylation of PA to yield diacylglycerol and Pi. The diacylglycerol generated in this reaction is used for the synthesis of the storage lipid triacylglycerol and for the synthesis of the membrane phospholipids phosphatidylcholine and phosphatidylethanolamine via the Kennedy Pathway. PA phosphatase is phosphorylated by cyclin‐dependent kinase (Cdk). Data indicate that Cdk phosphorylation down‐regulates PA phosphatase function. PA phosphatase is also dephosphorylated by the Nem1‐Spo7 complex, which results in an up‐regulation of PA phosphatase function. In this work, we examined the effects of phosphorylation and dephosphorylation of PA phosphatase on its cellular location, and on the composition of phospholipids and neutral lipids. In wild type cells, PA phosphatase is about equally distributed between the cytosolic and membrane fractions of the cell. A defect in Cdk phosphorylation of PA phosphatase caused an increase in the amount of enzyme associated with membranes, whereas a defect in the dephosphorylation of PA phosphatase caused a decrease in membrane association. Cdk phosphorylation of PA phosphatase caused a decrease in triacylglycerol content and an increase in phospholipid content. Conversely, dephosphorylation of the enzyme had the opposite effects. Supported by NIH grant GM 28140.