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Günther Daum, Institute of Biochemistry, Graz University of Technology, Austria;
Mitochondria are only partially autonomous organelles. The vast majority of their components, among them proteins and lipids need to be imported from other organelles. However, a small set of proteins and phospholipids, i.e. cardiolipin and phosphatidylethanolamine, are synthesized within mitochondria. In our laboratory the assembly of phospholipids into mitochondrial membranes has been studied in long term projects. As an experimental system for these investigations we employ the yeast Saccharomyces cerevisiae as a model system. Making use of molecular biological, cell biological and biochemical methods we were able to obtain a view of lipid traffic between organelles. Mitochondria play an important role in this process especially through their contribution to the pathway of aminoglycerophospholipid synthesis. The first lipid component of this pathway, phosphatidylserine, is formed in the endoplasmic reticulum; decarboxylation of phosphatidylserine by Psd1p, the major phosphatidylserine decarboxylase of the yeast, occurs in mitochondria; and further conversion of phosphatidylethanolamine to phosphatidylcholine by methyltransferases is localized to the endoplasmic reticulum. Thus, intense crosstalk of organelles is required for this pathway. Recently, we focussed on the molecular role and properties of the mitochondrial phosphatidylserine decarboxylase Psd1p. Biogenesis of this enzyme as well as defects in mitochondrial membranes caused by deletion of PSD1 and depletion of phosphatidylethanolamine were studied. These investigations demonstrated the important role of phosphatidylethanolamine as a mitochondrial lipid and revealed interesting counteracting effects of phosphatidylethanolamine with the mitochondria specific cardiolipin. Supported by the Austrian Science Fund (FWF).