High impact information on AFT1

• Strikingly, Cdk8-mediated modification of a single amino acid within Mediator represses the regulon of a single transcription factor, Rcs1/Aft1 [1].
• Recruitment of Tup1p and Cti6p regulates heme-deficient expression of Aft1p target genes [2].
• We have shown that Nhp6 interacts directly with the Aft1 N-half, including the DNA-binding region, to facilitate Aft1 binding at FRE2 UAS [3].
• Therefore, transcriptional activation in response to iron availability involves multiple protein interactions between the Aft1 iron-responsive DNA-binding factor and global regulators such as Nhp6 and Ssn6 [3].
• FRE2 encoding a plasma membrane ferric reductase is induced by the iron-responsive, DNA-binding, transcriptional activator Aft1 [3].

Biological context of AFT1

• Analysis of iron-regulated gene expression in Saccharomyces cerevisiae using cDNA microarrays has identified three putative cell wall proteins that are directly regulated by Aft1p, the major iron-dependent transcription factor in yeast [4].
• Aft2p, a novel iron-regulated transcription activator that modulates, with Aft1p, intracellular iron use and resistance to oxidative stress in yeast [5].
• FIT-deletion strains exhibited increased expression of Aft1p target genes as measured by a FET3-lacZ reporter gene or by Arn1p Western blotting, indicating that cells respond to the absence of FIT genes by up-regulating systems of iron uptake [4].
• The inability to grow on raffinose is not caused by the cell iron content being too low to sustain respiratory metabolism, because the oxygen consumption of aft1 mutants showed that their respiratory activity is 2-fold higher than that of controls [5].
• Sequences downstream of -490 harbor a consensus binding site for the iron regulatory factor Aft1p that is essential for iron regulation in wild-type strains [6].

Anatomical context of AFT1

• We demonstrated that under heme-depleted conditions, Aft1p-GFP was able to cycle normally between the nucleus and cytosol in response to cytosolic iron [7].
• This study has also revealed unexpected links between mitochondria and remote metabolic pathways since frataxin deficiency also enhances the expression of genes such as HSP30, that escape to AFT1 control [8].

Associations of AFT1 with chemical compounds

• Aft1p activation in FIT-deleted strains occurred when either ferrichrome or ferric salts were used as sources of iron during growth, suggesting that the FIT genes enhance uptake of iron from both sources [4].
• AFT1 was induced under acid shock response and under acid adaptation with lactic acid [9].
• Moreover, green fluorescent protein-fused Aft1p was localized to the nucleus in cells grown in media containing lactic acid, acetic acid, or hydrochloric acid [9].
• BIO5 is another Aft1-dependent gene induced both upon iron deprivation and in Deltagrx5 cells; this links iron and biotin metabolism [10].
• AFT1 encodes a 78 kDa protein with a highly basic amino terminal domain and a glutamine-rich C-terminal domain, reminiscent of transcriptional activators [11].

Physical interactions of AFT1

• Aft1p could also directly bind to Pse1p and was dissociated from the complex by Ran-GTP in vitro [12].
• Despite the inability to induce transcription under low iron conditions, chromatin immunoprecipitation demonstrated that Aft1p binds to the FET3 promoter in the absence of heme [7].
• This occurred despite the lack of an Aft1p-binding consensus region on the upstream region of SED1 or a high concentration of free iron [13].
• Truncated forms of Aft1p and Aft2p bound to a DNA duplex containing the Aft1p binding site in vitro [14].
• Grx3 and Grx4 interact with Aft1 as shown by two-hybrid interactions and co-immunoprecipitation assays [15].

Regulatory relationships of AFT1

• First, we found that FET4 expression is induced in iron-limited cells by the Aft1 iron-responsive transcriptional activator [16].
• Many Aft1-dependent genes involved in iron utilization that are up-regulated in a frataxin mutant were also up-regulated in the absence of Grx5 [10].
• This suggests that the interaction between Aft1p and Pse1p is not a critical step that controls the iron-regulated nucleo-cytoplasmic transport of Aft1p [12].
• Some of the AFT2-regulated genes are known to be regulated by Aft1p; however, AFT2-1(up)-dependent activation was independent of Aft1p [14].
• Glutaredoxins Grx3 and Grx4 regulate nuclear localisation of Aft1 and the oxidative stress response in Saccharomyces cerevisiae [17].

Other interactions of AFT1

• Iron regulation of SMF3 was dramatically reduced, but not completely eliminated, in strains lacking both the AFT1 and AFT2 iron regulatory factors [18].
• This report describes the properties of Aft2p, a protein 39% homologous to Aft1p [5].
• Four of the homologs (FRE3-FRE6) are specifically iron-regulated through the Aft1 transcription factor [19].
• Thus, the environmental signal resulting from iron deprivation was transduced through the regulated binding of AFT1 to the FET3 promoter, followed by the activation of transcription [20].
• The yeast genome contains five additional FRE1 and FRE2 homologues, four of which are regulated by iron and the major iron-dependent transcription factor, Aft1p, but whose function remains unknown [21].

Analytical, diagnostic and therapeutic context of AFT1

• RCS1 was one of a small group of genes identified in all three screens, and we used genetic and cell biological assays to confirm that it is required for chromosome stability [22].

References