<p>The eukaryotic proteins in this entry include frataxin, the protein that is mutated in Friedreich's ataxia [<cite idref="PUB00005550"/>], and related sequences. Friedreich's ataxia is a progressive neurodegenerative disorder caused by loss of function mutations in the gene encoding frataxin (FRDA). Frataxin mRNA is predominantly expressed in tissues with a high metabolic rate (including liver, kidney, brown fat and heart). Mouse and yeast frataxin homologues contain a potential N-terminal mitochondrial targeting sequence, and human frataxin has been observed to co-localise with a mitochondrial protein. Furthermore, disruption of the yeast gene has been shown to result in mitochondrial dysfunction. Friedreich's ataxia is thus believed to be a mitochondrial disease caused by a mutation in the nuclear genome (specifically, expansion of an intronic GAA triplet repeat) [<cite idref="PUB00005217"/>, <cite idref="PUB00004328"/>, <cite idref="PUB00003904"/>].</p><p>The bacterial proteins in this entry are iron-sulphur cluster (FeS) metabolism CyaY proteins hmologous to eukaryotic frataxin. Partial Phylogenetic Profiling [<cite idref="PUB00034422"/>] suggests that CyaY most likely functions as part of the ISC system for FeS cluster biosynthesis, and is supported by expermimental data in some species [<cite idref="PUB00042953"/>, <cite idref="PUB00042954"/>]. </p>