Aft2p, a Novel Iron-regulated Transcription Activator That Modulates, with Aft1p, Intracellular Iron Use and Resistance to Oxidative Stress in Yeast

The yeast, Saccharomyces cerevisiae, contains a transcription activator, Aft1p, that regulates the transcription of the high affinity iron transport system genes. This report describes the properties of Aft2p, a protein 39% homologous to Aft1p. Aft2p was found to activate transcription. Overproduction of Aft2p activates the transcription of the AFT1 target gene FET3. The double aft1aft2 mutant was unable to grow in iron-deprived conditions. Because a fet3 mutant does not show this deficiency, the defect is not solely caused by mis-regulation of iron transport but also involves defective iron use by the cells. The aft1 cells were unable to grow in aerobic conditions on plates containing raffinose as the sole carbon source. 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. The double aft1aft2 mutant also has many phenotypes related to oxidative stress such as H(2)O(2) hypersensitivity, oxygen-dependent copper toxicity, and oxygen-dependent methionine auxotrophy, which are suppressed in anaerobiosis. These results suggest that Aft2p and Aft1p have overlapping roles in the control of iron-regulated pathway(s) connected to oxidative stress resistance in yeast.