The aconitase function of iron regulatory protein 1. Genetic studies in yeast implicate its role in iron-mediated redox regulation.
Iron regulatory proteins (IRP) are sequence-specific RNA-binding proteins that mediate iron-responsive gene regulation in animals. IRP1 is also the cytosolic isoform of aconitase (c-aconitase). This latter activity could complement a mitochondrial aconitase mutation (aco1) in Saccharomyces cerevisiae to restore glutamate prototrophy. In yeast, the c-aconitase activity of IRP1 was responsive to iron availability in the growth medium. Although IRP1 expression rescued aco1 yeast from glutamate auxotrophy, cells remained growth-limited by glutamate, displaying a slow-growth phenotype on glutamate-free media. Second site mutations conferring enhanced cytosolic aconitase-dependent (ECA) growth were recovered. Relative c-aconitase activity was increased in extracts of strains harboring these mutations. One of the ECA mutations was found to be in the gene encoding cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDP2). This mutation, an insertion of a Ty delta element into the 5' region of IDP2, markedly elevates expression of Idp2p in glucose media. Our results demonstrate the physiological significance of the aconitase activity of IRP1 and provide insight into the role of c-aconitase with respect to iron and cytoplasmic redox regulation.
Narahari
J
J
Department of Microbiology and Immunology, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
Ma
R
R
Wang
M
M
Walden
W E
WE
D000154:Aconitate Hydratase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D005786:Gene Expression Regulation; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005816:Genetic Complementation Test; D018698:Glutamic Acid / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D035941:Iron Regulatory Protein 1; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D007521:Isocitrate Dehydrogenase / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D014170:Transformation, Genetic
D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D018698:Glutamic Acid; D007501:Iron; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+); D000154:Aconitate Hydratase; D035941:Iron Regulatory Protein 1