Acn9 is a novel protein of gluconeogenesis that is located in the mitochondrial intermembrane space

Previous studies have indicated that the Acn9 protein is involved in glucon eogenesis. Yeast mutants defective in the ACN9 gene display phenotypes iden tical with mutants defective in metabolic enzymes required for carbon assim ilation. These phenotypes include the inability to utilize acetate as a car bon and energy source, elevated levels of enzymes of the glyoxylate cycle, gluconeogenesis and acetyl-CoA. mobilization, and a deficiency in de novo s ynthesis of glucose from ethanol. The ACN9 gene was isolated by functional complementation of the acetate growth defect of an acn9 mutant. The open re ading frame corresponds to YDR511w, and encodes a protein of unknown functi on. Homologs have been identified in human, mouse, and nematode databases. Two mutant alleles were sequenced. The mutations altered amino acid residue s that are conserved among members of the new gene family. ACN9 gene expres sion was slightly repressed by glucose, and the level of the transcript was approximately 100-fold lower than that of glyoxylate or tricarboxylic acid cycle enzymes. A functional epitope-tagged form of Acn9 was expressed to s tudy expression and the subcellular localization of the protein. The tagged protein was localized to the mitochondrial intermembrane space.