The YFH1 gene is the Saccharomyces cerevisiae homologue of the human frataxin gene. In collaboration with Dr. Copeland and Dr. Resnick?s laboratories, we have found cells lacking YFH1 exhibit 1) accumulation of iron, which cannot be exported from the mitochondria; 2) oxidation of proteins; 3) oxidative DNA damage, which leads to petite colony formation with defects or loss of mitochondrial DNA and 4) nuclear chromosomal damage. The cellular impact of mitochondrial iron overload in yeast was determined by global gene expression profiling (in collaboration with the NIEHS Microarray Center) in an yfh1 deletion mutant with defective mitochondrial function and no mitochondrial DNA (i.e., rho0). Expression data for rho0 vs. yfh1 deletion mapped onto the yeast regulatory network of 22,605 protein-protein/protein-DNA interactions revealed YDR036C, Rcs1/Aft1, Mrps5, Hap4, Mrp4, Cox9, and Cad1 as important centers of activity. Interestingly, the yfh1 deletion profile harbored a large number of down regulated mitochondrial ribosomal proteins. This has never been reported before in studies involving frataxin and disruption of iron homeostasis in human or yeast cells. In order to better replicate the human disease process , we in collaboration with Dr. Mike Resnick also conducted transcription profiling on a yeast strain with a rheostatable system that can lead to a lowering of the expressing of the YFH1 gene. We examined the gene profiles in yeast in which frataxin was reduced twofold to sevenfold in generations 3 through 24, resulted in nearly identical events as those occurring in the knockout experiment. These transpired even with the initial reduction of frataxin at generation 3. Overall, we found the mostly downregulated cytochrome, heme, and iron/sulfur cluster assembly pathways, to indicate that frataxin has a role in iron transport, iron/sulfur cluster biosynthesis, oxidative phosphorylation, and as an antioxidant. Furthermore, we find these data correlate very well with a recently published iron deficiency profile. Interestingly, Puig and colleagues also demonstrate that, in response to iron deficiency, the S. cerevisiae Cth2 protein specifically downregulates mRNAs encoding proteins that participate in many Fe-dependent processes by binding to specific AU-rich elements in the 3' untranslated region of mRNAs targeted for degradation. They conclude that this facilitates the utilization of limited cellular iron levels for other ?more important? processes in the cell. Our data supports this theory by finding that proteins involved in DNA repair, for example, but that also need iron-sulfur centers, are not downregulated. Instead, these proteins show no change or are induced in the gene expression profile.
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