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.

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Journal Article | Research Support, Non-U.S. Gov't | Research Support, U.S. Gov't, P.H.S.

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Rutherford JC, Jaron S, Ray E, Brown PO, Winge DR

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