A Mutation in a Purported Regulatory Gene Affects Control of Sterol Uptake in Saccharomyces cerevisiae

Abstract

Aerobically growing wild-type strains of Saccharomyces cerevisiae are unable to take exogenously supplied sterols from media. This aerobic sterol exclusion is vitiated under anaerobic conditions, in heme-deficient strains, and under some conditions of impaired sterol synthesis. Mutants which can take up sterols aerobically in heme-competent cells have been selected. One of these mutations, designated upc2-1, gives a pleiotropic phenotype in characteristics as diverse as aerobic accumulation of sterols, total lipid storage, sensitivity to metabolic inhibitors, response to altered sterol structures, and cation requirements. During experiments designed to ascertain the effects of various cations on yeast with sterol alterations, it was observed that upc2-1was hypersensitive to Ca2+. Using resistance to Ca2+ as a screening vehicle, we cloned UPC2 and showed that it is YDR213W, an open reading frame on chromosome IV. This belongs to a fungal regulatory family containing the Zn(II)2Cys6 binuclear cluster DNA binding domain. The single guanine-to-adenine transition in upc2-1 gives a predicted amino acid change from glycine to aspartic acid. The regulatory defect explains the semidominance and pleiotropic effects of upc2-1.

The essential gene YMR134W from Saccharomyces cerevisiae is important for appropriate mitochondrial iron utilization and the ergosterol biosynthetic pathway

“…It is well accepted that heme (an iron cofactor synthesized into mitochondria) is the oxygen sensor molecule in yeast and that this pathway is mediated by the Heme Activator Protein (Hap1p) [22]. In particular, Hap1p induces the expression of ROX1 repressor that, in turn, inhibits the expression of the ergosterol import system from extracellular media in the presence of oxygen [23]. So, ergosterol supplementation under aerobic conditions is not effective in reverting phenotype of mutant genes involved in ergosterol biosynthesis because the absence of its importer system.…”

The zinc cluster proteins Upc2 and Ecm22 promote filamentation in Saccharomyces cerevisiae by sterol biosynthesis‐dependent and ‐independent pathways

“…As overexpression of SUT1 and SUT2 leads to inhibition of filamentous growth, we asked whether Ecm22 and Upc2, which are like Sut1 and Sut2 zinc cluster proteins that regulate sterol import (Bourot and Karst, 1995;Schjerling and Holmberg, 1996;Crowley et al, 1998;Ness et al, 2001;Shianna et al, 2001), also control filamentous growth. Rather unexpectedly, overexpression of either ECM22 or UPC2 resulted in much stronger haploid invasive growth compared with the wild type ( Fig.…”

“…Sterol uptake is also regulated by Upc2 and its paralogue Ecm22, which like Sut1 and Sut2, are members of the zinc cluster protein family (Schjerling and Holmberg, 1996;Crowley et al, 1998;Shianna et al, 2001). Like Sut1, Upc2 induces expression of AUS1 and DAN1, and another gene involved in sterol uptake, PDR11, under anaerobic conditions (Abramova et al, 2001;Wilcox et al, 2002).…”

Involvement of Snf7p and Rim101p in the transcriptional regulation of TIR1 and other anaerobically upregulated genes in Saccharomyces cerevisiae

“…Repression also seems to rely on Mot3p, Mox1p, Mox2p and the Tup1/Ssn6 complex . The transcription factors UPC2 and ECM22 are involved in the anaerobic induction of the genes involved in sterol import (Crowley et al, 1998;Shianna et al, 2001;Wilcox et al, 2002;ter Linde et al, 2003). Although these regulators control a substantial number of anaerobically upregulated genes, the transcriptional upregulation of many other 'anaerobic' genes has not been attributed to specific regulators.…”