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Abstract
Genes involved in lipid accumulation were identified in Saccharomyces cerevisiae using transposon insertion mutagenesis. Five ORFs, such as SNF2, IRA2, PRE9, PHO90, and SPT21 were found from the analysis of the insertion sites in transposon insertion mutants with higher lipid content. Since these ORFs are not directly involved in storage lipid biosynthesis, we speculate that they are involved in carbon fluxes into storage lipids in response to nutrient conditions. Lipid analysis of disruptants of these ORFs indicated that the Δsnf2, and Δira2 disruptants had significantly higher lipid content. Cultivation in a nitrogen-limited medium increased the lipid content in all disruptants, among which the Δpre9 disruptant was the most sensitive to nitrogen limitation. We then focused on the Δsnf2 disruptant due to its higher lipid content and its function as a regulator of phospholipid synthesis. Lipid class analysis indicated that triacylglycerol and free fatty acids contributed to the increase in total lipids of the Δsnf2 disruptant. The addition of exogenous fatty acids was not so effective at increasing the lipid content in the Δsnf2 disruptant as it was in the wild type. It should be noticed that exogenous free linoleic acid was much higher in the Δsnf2 disruptant than in the wild type, as in the case of endogenous free fatty acids. In addition, the incorporation of exogenous fatty acids into cells increased in the disruptant, suggesting that fatty acid transporters were regulated by SNF2. The results suggest that metabolic fluxes into storage lipids, which are activated in the Δsnf2 disruptant, is repressed by the incorporation of exogenous fatty acids. They provide new insight into the biosynthesis of storage lipids in yeast.
