Alternative start sites in the Saccharomyces cerevisiae GLR1 gene are responsible for mitochondrial and cytosolic isoforms of glutathione reductase.
To combat oxidative damage, eukaryotic cells have evolved with numerous anti-oxidant factors that are often distributed between cytosolic and mitochondrial pools. Glutathione reductase, which regenerates the reduced form of glutathione, represents one such anti-oxidant factor, yet nothing is known regarding the partitioning of this enzyme within the cell. Using the bakers' yeast Saccharomyces cerevisiae as a model, we provide evidence that a single gene, namely GLR1, encodes both the mitochondrial and cytosolic forms of glutathione reductase. A deletion in GLR1 drastically increases levels of oxidized glutathione in these two subcellular compartments. The GLR1 gene has two inframe start codons that are both used as translation initiation sites. Translation from the first codon generates the mitochondrial form that includes a mitochondrial targeting signal, whereas translation from the second codon produces the cytosolic form that lacks this sequence. Our results indicate that the sequence context of the two AUG codons influences the efficiency of translation initiation at each site, which in turn affects the relative levels of cytosolic and mitochondrial Glr1p. This method of subcellular distribution of glutathione reductase may be conserved in mammalian cells as well.
Outten
Caryn E
CE
Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205, USA.
Culotta
Valeria C
VC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003062:Codon; D003600:Cytosol / Q000201:enzymology*; D016368:Frameshift Mutation; D017353:Gene Deletion; D005978:Glutathione / Q000032:analysis / Q000378:metabolism; D005980:Glutathione Reductase / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D014176:Protein Biosynthesis; D012331:RNA, Fungal / Q000737:chemistry; D012333:RNA, Messenger / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000648:ultrastructure; D016415:Sequence Alignment
D003062:Codon; D012331:RNA, Fungal; D012333:RNA, Messenger; D005980:Glutathione Reductase; D005978:Glutathione