Genetic Control of Membrane Assembly in Yeast

Abstract

The synthesis of the membrane-forming phospholipids is a highly regulated process in yeast. Figure 1 summarizes the biosynthetic pathways of the major phospholipids in yeast. A number of enzymes in the de novo pathway for the synthesis of the major phospholipid, phosphatidylcholine (PtdCho), in Saccharomyces cerevisiae are subject to coordinate regulation [Carman & Henry, 1989]. These enzymes include CDP-diacylglycerol synthase [Homann et al., 1985], phosphatidylserine synthase [Klig et al., 1985; Poole et al., 1986] and the phospholipid-JV-methyltransferases [Carson et al., 1984; Klig et al., 1985; Summers et al., 1988; Waechter & Lester, 1973; Yamashita et al., 1982]. Interestingly, the cytosolic enzyme, inositol-1-phosphate synthase, is also regulated in coordination with the other, membrane associated enzymes [Hirsch & Henry, 1985]. All of these enzymes exhibit a common pattern of regulation [Carman & Henry, 1989, Henry et al., 1984] : they are fully derepressed in the absence of inositol and choline, they are partially repressed in the presence of inositol and they are fully repressed in the presence of inositol plus choline. Choline alone without inositol has no repressing effect.