Phosphatidylcholine Biosynthesis in Saccharomyces cerevisiae: Effects on Regulation of Phospholipid Synthesis and Respiratory Competence

Abstract

Phosphatidylcholine (PC) can be synthesized via two distinct pathways. One pathway involves three sequential methylations of phosphatidylethanolamine (PE) (Bremer et al. , 1960). Alternatively, PC can be synthesized from free choline via the CDP-choline pathway (Kennedy and Weiss, 1956). These two pathways are found in all eukaryotes so far investigated, including mammals (Bjomstad and Bremer, 1966) and yeast (Steiner and Lester, 1972; Waechter and Lester, 1973). Phospholipid biosynthesis is highly regulated in yeast. Much of the regulation occurs at the level of gene transcription in response to the soluble precursors of phospholipid biosynthesis, inositol and choline (for review see Carman and Henry, 1989; Paltauf et al. , 1992). In the presence of inositol, transcription of the coregulated biosynthetic genes IN01-Inositol-1-phosphate synthase, CHOI -Phosphatidylserine synthase, CH02/PEM1 - Phosphatidylethanolamine methyltransferase and OPI3/PEM2 -Phospholipid methyltransferase) (Figure 1) is repressed. In the absence of inositol, transcription of these genes is derepressed. If choline is added to medium in which inositol is already present, these genes are further repressed. However, if choline is present in the growth medium by itself, it has little or no effect on transcription of the co-regulated genes.