title: Cumulative mutations affecting sterol biosynthesis in the yeast Saccharomyces cerevisiae result in synthetic lethality that is suppressed by alterations in sphingolipid profiles.
abstract: UPC2 and ECM22 belong to a Zn(2)-Cys(6) family of fungal transcription factors and have been implicated in the regulation of sterol synthesis in Saccharomyces cerevisiae and Candida albicans. Previous reports suggest that double deletion of these genes in S. cerevisiae is lethal depending on the genetic background of the strain. In this investigation we demonstrate that lethality of upc2Delta ecm22Delta in the S288c genetic background is attributable to a mutation in the HAP1 transcription factor. In addition we demonstrate that strains containing upc2Delta ecm22Delta are also inviable when carrying deletions of ERG6 and ERG28 but not when carrying deletions of ERG3, ERG4, or ERG5. It has previously been demonstrated that UPC2 and ECM22 regulate S. cerevisiae ERG2 and ERG3 and that the erg2Delta upc2Delta ecm22Delta triple mutant is also synthetically lethal. We used transposon mutagenesis to isolate viable suppressors of hap1Delta, erg2Delta, erg6Delta, and erg28Delta in the upc2Delta ecm22Delta genetic background. Mutations in two genes (YND1 and GDA1) encoding apyrases were found to suppress the synthetic lethality of three of these triple mutants but not erg2Delta upc2Delta ecm22Delta. We show that deletion of YND1, like deletion of GDA1, alters the sphingolipid profiles, suggesting that changes in sphingolipids compensate for lethality produced by changes in sterol composition and abundance.
authors.affiliation: Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, 40536.
authors.forename: Martin
authors.initials: M
authors.lastname: Valachovic
authors.forename: Bart M
authors.initials: BM
authors.lastname: Bareither
authors.forename: M
authors.initials: M
authors.lastname: Shah Alam Bhuiyan
authors.forename: James
authors.initials: J
authors.lastname: Eckstein
authors.forename: Robert
authors.initials: R
authors.lastname: Barbuch
authors.forename: Dina
authors.initials: D
authors.lastname: Balderes
authors.forename: Lisa
authors.initials: L
authors.lastname: Wilcox
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Sturley
authors.forename: Robert C
authors.initials: RC
authors.lastname: Dickson
authors.forename: Martin
authors.initials: M
authors.lastname: Bard
mesh_terms: D002176:Candida albicans / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D005800:Genes, Fungal; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D013107:Sphingolipids / Q000096:biosynthesis* / Q000235:genetics; D013261:Sterols / Q000096:biosynthesis*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids; D013261:Sterols