Reduction of CDP-diacylglycerol synthase activity results in the excretion of inositol by Saccharomyces cerevisiae.
A yeast mutant, cdg1, was isolated on the basis of an inositol excretion phenotype. This mutant exhibited pleiotropic deficiencies in phospholipid biosynthesis, including reduced levels of CDP-diacylglycerol (DAG) synthase activity (Klig, L. S., Homann, M. J., Kohlwein, S. D., Kelley, M. J., Henry, S. A., and Carman, G. M. (1988) J. Bacteriol. 170, 1878-1886). In this study we present evidence that the molecular basis for the inositol excretion phenotype is a G305/A305 point mutation (Cys102 --> Tyr substitution) within the CDS1 gene (encodes CDP-DAG synthase) of this mutant. Expression of CDP-DAG synthase activity from a plasmid-borne copy of the CDS1 gene in the cdg1 mutant was not down-regulated, and this expression also corrected the inositol excretion phenotype. Introduction of the above mutated gene (CDS1*) controlled by its endogenous promoter on a single copy plasmid into a cds1-null background reconstituted a transformant with the cdg1 phenotype, including reduced CDP-DAG synthase activity, elevated phosphatidylserine synthase activity, and inositol excretion into the growth medium. Expression of CDS1* in a single copy in the cdg1 mutant raised CDP-DAG synthase activity from 15 to 30% of derepressed wild-type yeast levels but still did not correct the inositol excretion phenotype. CDP-DAG synthase activity was not regulated in response to precursors of phospholipid biosynthesis in the cdg1 mutant either with or without a trans copy of the CDS1* gene. An open reading frame was identified 5' to the CDS1 locus, YBR0314, which also resulted in inositol excretion when present in trans in multiple copies.
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, Texas 77225, USA. wdowhan@utmmg.med.uth.tmc.edu
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D002798:Diacylglycerol Cholinephosphotransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005816:Genetic Complementation Test; D007294:Inositol / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000096:biosynthesis; D010716:Phosphatidylinositols / Q000096:biosynthesis; D017354:Point Mutation; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D007294:Inositol; D002798:Diacylglycerol Cholinephosphotransferase