Rutherford J C, Jaron S, Ray E, Brown P O, Winge D R
University of Utah Health Sciences Center, Department of Medicine, Salt Lake City, Utah 84132, USA.
Proc Natl Acad Sci U S A. 2001 Dec 4;98(25):14322-7. doi: 10.1073/pnas.261381198.
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.
酿酒酵母中的铁稳态在转录水平上由Aft1p调控，Aft1p在低铁条件下激活其靶基因的表达。酵母基因组包含AFT1的一个旁系同源基因，已将其命名为AFT2。为了确定AFT1和AFT2是否具有重叠功能，构建了一个包含双缺失aft1Δaft2Δ的突变体。生长试验表明，单缺失aft2Δ菌株没有表现出铁依赖性表型。然而，双突变aft1Δaft2Δ菌株比单突变aft1Δ菌株对低铁生长条件更敏感。AFT2的一个突变等位基因（AFT2-1(up)）或野生型AFT2基因的过表达导致aft1Δ菌株呼吸缺陷表型的部分互补。AFT2-1(up)等位基因也增加了aft1Δ菌株对(59)Fe的摄取。利用DNA微阵列鉴定受AFT2调控的基因。一些受AFT2调控的基因已知也受Aft1p调控；然而，AFT2-1(up)依赖性激活独立于Aft1p。由AFT2-1(up)等位基因激活的两个基因的诱导动力学与Aft2p作为直接转录因子的作用一致。在体外，Aft1p和Aft2p的截短形式与包含Aft1p结合位点的DNA双链结合。AFT2的野生型等位基因在低铁条件下生长时激活转录。总之，这些数据表明酵母的铁调节子有第二条调控途径，AFT1和AFT2发挥部分冗余作用。
