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In the yeast Saccharomyces cerevisiae, the absence of the pseudouridine synthase Pus3/Deg1, which modifies tRNA positions 38 and 39, results in increased lipid droplet (LD) content and translational defects. In addition, starvation‐like transcriptome alterations and induced protein aggregation were observed. In this study, we show that the deg1 mutant increases specific misreading errors. This could lead to altered expression of the main regulators of neutral lipid synthesis which are the acetyl‐CoA carboxylase (Acc1), an enzyme that catalyzes a key step in fatty acid synthesis, and its regulator, the Snf1/AMPK kinase. We demonstrate that upregulation of the neutral lipid content of LD in the deg1 mutant is achieved by a mechanism operating in parallel to the known Snf1/AMPK kinase‐dependent phosphoregulation of Acc1. While in wild‐type cells removal of the regulatory phosphorylation site (Ser‐1157) in Acc1 results in strong upregulation of triacylglycerol (TG), but not steryl esters (SE), the deg1 mutation more specifically upregulates SE levels. In order to elucidate if other lipid species are affected, we compared the lipidomes of wild type and deg1 mutants, revealing multiple altered lipid species. In particular, in the exponential phase of growth, the deg1 mutant shows a reduction in the pool of phospholipids, indicating a compromised capacity to mobilize acyl‐CoA from storage lipids. We conclude that Deg1 plays a key role in the coordination of lipid storage and mobilization, which in turn influences lipid homeostasis. The lipidomic effects in the deg1 mutant may be indirect outcomes of the activation of various stress responses resulting from protein aggregation. [ABSTRACT FROM AUTHOR]

During applications of 5-fluorocytosine (5FC) and fluconazole (FLC), additive or synergistic action may even occur when primary resistance to 5FC is established. Here, we analysed conjoint drug action in Saccharomyces cerevisiae strains deficient in genes known to be essential for 5FC or FLC function. Despite clear primary resistance, residual 5FC activity and additive 5FC + FLC action in cells lacking cytosine permease (Fcy2p) or uracil phosphoribosyl transferase (Fur1p) were detected. In contrast, [DELTA]fcy1 mutants, lacking cytosine deaminase, became entirely resistant to 5FC, concomitantly losing 5FC+FLC additivity. Disruption of the orotate phosphoribosyltransferase gene (URA5) in the wild-type led to low-level 5FC tolerance, while an alternative orotate phosphoribosyltransferase, encoded by URA 10, contributed to 5FC toxicity only in the [DELTA]ura5 background. Remarkably, combination of [DELTA]ura5 and [DELTA]furl resulted in complete 5FC resistance. Thus, yeast orotate phosphoribosyltransferases are involved in 5FC metabolism. Similarly, disruption of the ergosterol [[DELTA].sup.5,6]-desaturase-encoding gene ERG3 resulted only in partial resistance to FLC, and concomitantly a synergistic effect with 5FC became evident. Full resistance to FLC occurred in [DELTA]erg3 [DELTA]erg11 double mutants and, simultaneously, synergism or even an additive effect with FLC and 5FC was no longer discernible. Since the majority of spontaneously occurring resistant yeast clones displayed residual sensitivity to either 5FC or FLC and those strains responded to combined drug treatment in a predictable manner, careful resistance profiling based on the findings reported here may help to address yeast infections by combined application of antimycotic compounds.

Heterologous expression in Saccharomyces cerevisiae is used to identify the gene responsible for self-protection in the Pichia acaciae killer plasmid system. It is revealed that dose-independent protection by Pichia acaciae (pPacl-2)-ORF4 and intracellular interference with toxin function suggests toxin reinternalization in immune killer cells.