Heme levels switch the function of Hap1 of Saccharomyces cerevisiae between transcriptional activator and transcriptional repressor

Mark J. Hickman, Fred Winston

Research output: Contribution to journalArticlepeer-review

91 Scopus citations

Abstract

Changes in oxygen levels cause widespread changes in gene expression in organisms ranging from bacteria to humans. In Saccharomyces cerevisiae, this response is mediated in part by Hap1, originally identified as a heme-dependent transcriptional activator that functions during aerobic growth. We show here that Hap1 also plays a significant and direct role under hypoxic conditions, not as an activator, but as a repressor. The repressive activity of Hap1 controls several genes, including three ERG genes required for ergosterol biosynthesis. Chromatin immunoprecipitation experiments showed that Hap1 binds to the ERG gene promoters, while additional experiments showed that the corepressor Tup1/Ssn6 is recruited by Hap1 and is also required for repression. Furthermore, mutational analysis demonstrated that conserved Hap1 binding sites in the ERG5 5′ regulatory region are required for repression. The switch of Hap1 from acting as a hypoxic repressor to an aerobic activator is determined by heme, which is synthesized only in the presence of oxygen. The ability of Hap1 to function as a ligand-dependent repressor and activator is a property shared with mammalian nuclear hormone receptors and likely allows greater transcriptional control by Hap1 in response to changing oxygen levels.

Original languageEnglish (US)
Pages (from-to)7414-7424
Number of pages11
JournalMolecular and cellular biology
Volume27
Issue number21
DOIs
StatePublished - Nov 2007

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Cell Biology

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