Transcriptional Regulation of the Two Sterol Esterification Genes in the Yeast Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae transcribes two genes, ARE1 and ARE2, that contribute disproportionately to the esterification of sterols. Are2p is the major enzyme isoform in a wild-type cell growing aerobically. This likely results from a combination of differential transcription initiation and transcript stability. By using ARE1 and ARE2 promoter fusions to lacZ reporters, we demonstrated that transcriptional initiation from the ARE1 promoter is significantly reduced compared to that from the ARE2 promoter. Furthermore, the half-life of the ARE2 mRNA is approximately 12 times as long as that of the ARE1 transcript. We present evidence that the primary role of the minor sterol esterification isoform encoded by ARE1 is to esterify sterol intermediates, whereas the role of the ARE2 enzyme is to esterify ergosterol, the end product of the pathway. Accordingly, the ARE1 promoter is upregulated in strains that accumulate ergosterol precursors. Furthermore, ARE1 and ARE2 are oppositely regulated by heme. Under heme-deficient growth conditions, ARE1 was upregulated fivefold while ARE2 was down-regulated. ARE2 requires the HAP1 transcription factor for optimal expression, and both ARE genes are derepressed in a rox1 (repressor of oxygen) mutant genetic background. We further report that the ARE genes are not subject to end product inhibition; neither ARE1 nor ARE2 transcription is altered in an are mutant background, nor does overexpression of either ARE gene alter the response of the ARE-lacZ reporter constructs. Our observations are consistent with an important physiological role for Are1p during anaerobic growth when heme is limiting and sterol precursors may accumulate. Conversely, Are2p is optimally required during aerobiosis when ergosterol is plentiful.

Biosynthesis of Phytosterol Esters: Identification of a Sterol O-Acyltransferase in Arabidopsis

“…The SE composition resulting from expression of AtSAT1 was clearly different from reports of overexpressing the ARE1 and ARE2 genes in SCY059, which produced SE enriched in zymosterol and erogosterol (Jensen-Pergakes et al, 2001). Thus, it can also be inferred that sterol preference of AtSAT1 is distinctively different from that of the yeast sterol O-acyltransferases.…”

Genetic Architecture of Ethanol-Responsive Transcriptome Variation in Saccharomyces cerevisiae Strains

“…The S288c background has several mutations in regulators of respiration and carbon metabolism, including Hap1p and Mig3p (Gaisne et al 1999;Lewis and Gasch 2012); however several of the hotspots we observe are cross specific, indicating that natural variation in carbon responses in wild strains also contributes to differences in ethanol tolerance (Lewis et al 2010). Hap1p also controls genes involved in ergosterol biosynthesis, which affects membrane fluidity and thus ethanol tolerance (Kennedy et al 1999;Jensen-Pergakes et al 2001;Tamura et al 2004). Likewise, variation in fatty acid consumption, controlled in part by the Oaf1 transcription factor, can alter the membrane content of cells to directly affect ethanol resistance (Chi and Arneborg 1999;You et al 2003;Lockshon et al 2007).…”

“…None of the pairs of hotspots with overlapping target sets shown in Figure 4 were identified as epi-hotspots, indicating that most of the overlap we initially observed represents additive hotspot effects. However, we uncovered several other epi-hotspots involving two or more regions implicated from the 1D mapping regimes: for example the interaction between peak 13 (Hap1p) and peak 1 (Oaf1p) represents an epi-hotspot-the candidate regulators encoded at these loci both affect membrane fluidity through ergosterol (Kennedy et al 1999;Jensen-Pergakes et al 2001;Tamura et al 2004) and fatty acid composition (Karpichev et al 1997;Karpichev et al 2008), respectively. Several loci were associated with multiple epi-hotspots, including peak 13 (HAP1) linked to four epi-hotspots, and peak 4 (MAT-ALPHA1), peak 7 (URA3), peak 12, peak 17 (MKT1), and peak 31 (FAA2) that were each linked to three epi-hotspots.…”

Genome-Wide Expression Profile of Sake Brewing Yeast under Shaking and Static Conditions

“…Genes involved in ergosterol biosynthesis were overexpressed under shaking and/or static conditions. Furthermore, two genes that are involved in sterol ester homeostasis and that were overexpressed in K-9 under static conditions are ARE2 11,12) and YEH1. 13) All yeast cells convert large amounts of ergosterol to sterol ester, which is stored in lipid particles as a reservoir for eventual use in the cell membrane.…”