REGULATION OF PHOSPHATIDYLGLYCEROPHOSPHATE SYNTHASE LEVELS IN SACCHAROMYCES-CEREVISIAE

The PGS1 gene of Saccharomyces cerevisiae encodes phosphatidylglycerop hosphate (PG-P) synthase. PG-P synthase activity is regulated by facto rs affecting mitochondrial development and through cross-pathway contr ol by inositol. The molecular mechanism of this regulation was examine d by using a reporter gene under control of the PGS1 gene promoter (P- PGS1-lacZ). Gene expression subject to carbon source regulation was mo nitored both at steady-state level and during the switch between diffe rent carbon sources. Cells grown in a non-fermentable carbon source ha d beta-galactosidase levels 3-fold higher than those grown in glucose. A shift from glucose to lactate rapidly raised the level of gene expr ession, whereas a shift back to glucose had the opposite effect. In ei ther a pgs1 null mutant or a rho mutant grown in glucose, P-PGS1-lacZ expression was 30-50% of the level in wild type cells. Addition of ino sitol to the growth medium resulted in a 2-3-fold reduction in gene ex pression in wild type cells. In ino2 and ino8 mutants, gene expression was greatly reduced and was not subject to inositol regulation consis tent with inositol repression being dependent on the INO2 and INO4 reg ulatory genes. P(PGS1)-lacZ expression was elevated in a cds1 null mut ant in the presence or absence of inositol, indicating that the capaci ty to synthesize CDP-diacylglycerol affects gene expression. Lack of c ardiolipin synthesis (cls1 null mutant) had no effect on reporter gene expression.