Fep1, an Iron Sensor Regulating Iron Transporter Gene Expression in Schizosaccharomyces pombe

Abstract

Schizosaccharomyces pombe cells acquire iron under high affinity conditions through the action of a cell surface ferric reductase encoded by the frp1 ؉ gene and a two-component iron-transporting complex encoded by the fip1 ؉ and fio1 ؉ genes. When cells are grown in the presence of iron, transcription of all three genes is blocked. A conserved regulatory element, 5-(A/ T)GATAA-3, located upstream of the frp1 ؉ , fip1 ؉ , and fio1 ؉ genes, is necessary for iron repression. We have cloned a novel gene, termed fep1 ؉ , which encodes an iron-sensing transcription factor. Binding studies reveal that the putative DNA binding domain of Fep1 expressed as a fusion protein in Escherichia coli specifically interacts with the 5-(A/T)GATAA-3 sequence in an iron-dependent manner. In a fep1⌬ mutant strain, the fio1 ؉ gene is highly expressed and is unregulated by iron. Furthermore, the fep1⌬ mutation increases activity of the cell surface iron reductase and renders cells hypersensitive to the iron-dependent free radical generator phleomycin. Mutations in the transcriptional corepressors tup11 ؉ and tup12 ؉ are phenocopies to fep1 ؉ . Indeed, strains with both tup11⌬ and tup12⌬ deletions fail to sense iron. This suggests that in the presence of iron and Fep1, the Tup11 and Tup12 proteins may act as co-repressors for down-regulation of genes encoding components of the reductive iron transport machinery.

Individual letters of the RNA polymerase II CTD code govern distinct gene expression programs in fission yeast

“…The GATA-family transcription factor Fep1 represses expression of the aforementioned iron uptake genes under iron-replete growth conditions (10,14). Fep1 binds in an iron-dependent manner to a GATA sequence element [5′-ATC(A/T)GATA(A/T)] in the regulatory regions upstream of the repressible iron uptake genes.…”

“…These include, in addition to Fep1, the corepressors Tup11 and Tup12 (10,14). However, this scenario was vitiated by the findings that the Fep1, Tup11, and Tup12 mRNA levels, gauged by RNA-seq, were not affected significantly by the Y1F, S2A, Y1F•S7A, or S2A•S7A mutations (Fig.…”

“…If the derepression of the iron regulon at the mRNA level is physiologically important, we would expect to see increased activity of Fep1 regulated proteins in cells bearing the Y1F and S2A CTD mutations. We assayed ferric reductase Frp1 activity by overlaying cells grown on ironreplete medium with agar containing the ferric reductase substrate triphenyltetrazolium chloride, which is reduced by cell surface-associated Frp1 to yield a red pigmented product (14). This assay distinguished the pale WT, S7A, and T4A colonies from the red Y1F, Y1F•S7A, and S2A•S7A colonies (Fig.…”

“…Derepression of the Fep1-regulated iron uptake regulon causes hypersensitivity to phleomycin toxicity (14) by virtue of increasing the available intracellular iron. The salient findings were that Y1F, S2A, Y1F•S7A, and S2A•S7A strains failed to grow in the presence of 10 μg/mL phleomycin, a concentration of drug that did not prevent growth of the WT, S7A, and T4A strains (Fig.…”

Cells Lacking Pfh1, a Fission Yeast Homolog of Mammalian Frataxin Protein, Display Constitutive Activation of the Iron Starvation Response

“…b Number of proteins up-regulated is more than 1.5-fold in ⌬pfh1 versus wild-type cells after 3 h under aerobic conditions. c The genes coding for these proteins are up-regulated upon iron starvation (41), probably in a Fep1-dependent manner (52). d Six of these proteins are included in the set of proteins induced by Pap1.…”