title: A second iron-regulatory system in yeast independent of Aft1p.
abstract: Iron homeostasis in the yeast Saccharomyces cerevisiae is regulated at the transcriptional level by Aft1p, which activates the expression of its target genes in response to low-iron conditions. The yeast genome contains a paralog of AFT1, which has been designated AFT2. To establish whether AFT1 and AFT2 have overlapping functions, a mutant containing a double aft1Deltaaft2Delta deletion was generated. Growth assays established that the single aft2Delta strain exhibited no iron-dependent phenotype. However, the double-mutant aft1Deltaaft2Delta strain was more sensitive to low-iron growth conditions than the single-mutant aft1Delta strain. A mutant allele of AFT2 (AFT2-1(up)), or overexpression of the wild-type AFT2 gene, led to partial complementation of the respiratory-deficient phenotype of the aft1Delta strain. The AFT2-1(up) allele also increased the uptake of (59)Fe in an aft1Delta strain. DNA microarrays were used to identify genes regulated by AFT2. Some of the AFT2-regulated genes are known to be regulated by Aft1p; however, AFT2-1(up)-dependent activation was independent of Aft1p. The kinetics of induction of two genes activated by the AFT2-1(up) allele are consistent with Aft2p acting as a direct transcriptional factor. Truncated forms of Aft1p and Aft2p bound to a DNA duplex containing the Aft1p binding site in vitro. The wild-type allele of AFT2 activated transcription in response to growth under low-iron conditions. Together, these data suggest that yeast has a second regulatory pathway for the iron regulon, with AFT1 and AFT2 playing partially redundant roles.
authors.affiliation: University of Utah Health Sciences Center, Department of Medicine, Salt Lake City, Utah 84132, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Rutherford
authors.forename: S
authors.initials: S
authors.lastname: Jaron
authors.forename: E
authors.initials: E
authors.lastname: Ray
authors.forename: P O
authors.initials: PO
authors.lastname: Brown
authors.forename: D R
authors.initials: DR
authors.lastname: Winge
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D005800:Genes, Fungal; D006706:Homeostasis; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C090297:AFT1 protein, S cerevisiae; C436328:Aft2 protein, S cerevisiae; D004271:DNA, Fungal; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D007501:Iron