8 Regulation and Compartmentalization of Lipid Synthesis in Yeast

I. INTRODUCTION The membrane lipids of Saccharomyces cerevisiae are similar to those of other eukaryotic organisms. Yeast synthesizes sterols, and its membranes contain a typically eukaryotic mixture of phospholipids, including phosphatidylcholine and inositol-containing phospholipids. Unlike other eukaryotes, however, S. cerevisiae does not synthesize ether lipids, and its fatty acids are predominantly 16 and 18 carbons in length. Considerable progress has recently been made in determining how the biosynthesis of phospholipids is compartmentalized within the yeast cell and how phospholipids are transported between membrane compartments. In addition, during the decade since the first edition of The Molecular Biology of the Yeast Saccharomyces was published, remarkable progress has been made in characterizing the enzymes of phospholipid biosynthesis and identifying and isolating their structural genes. A combination of molecular and genetic studies has revealed a complex pattern of regulation governing the expression of a number of genes encoding phospholipid biosynthetic enzymes. Because of its powerful genetics and molecular biology, yeast will be an increasingly important organism for the analysis of these processes, which are crucial to all eukaryotic organisms. II. PATHWAYS OF LIPID SYNTHESIS AND UPTAKE OF LIPIDS INTO YEAST CELLS The lipid matrices of all subcellular membranes of yeast are composed of essentially the same set of polar lipids and sterols. However, the relative proportions of individual lipid classes vary considerably between different organelle membranes. Furthermore, the lipid compositions of particular membranes can be varied significantly by altering growth conditions such as temperature, nutrient supply, oxygen concentration, and growth rate. In addition,...