Unlike pathogenic fungi, the budding yeast Saccharomyces cerevisiae is not efficient in using heme as nutritional source of iron. Here we report that, in this yeast, heme uptake is induced under conditions of heme starvation. Heme synthesis requires oxygen, and yeast grown anaerobically exhibited an increased uptake of hemin. Similarly, a strain lacking aminolevulinate synthase exhibited a 6-fold increase in hemin uptake when grown without 2-aminolevulinic acid. We used microarray analysis of cells grown under reduced oxygen tension or reduced intracellular heme to identify candidate genes involved in heme uptake. Surprisingly, overexpression of PUG1 (for Protoporphyrin Uptake Gene 1) resulted in reduced utilization of exogenous heme by a heme deficient strain and, conversely, increased utilization of protoporphyrin IX. Pug1p was localized to the plasma membrane by indirect immunofluorescence and subcellular fractionation. Strains overexpressing PUG1 exhibited decreased accumulation of (55)Fe-hemin, but increased accumulation of protoporphyrin IX, when compared to the wild type strain. To measure the effect of PUG1 overexpression on intracellular heme pools, we used a CYC1-LacZ reporter, which is activated in the presence of heme, and we monitored the activity of a heme-containing metalloreductase, Fre1p, expressed from constitutive promoter. Data from these experiments were consistent with a role for Pug1p in inducible protoporphyrin IX influx and heme efflux.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Annotation Extension||Reference|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Assay||Construct||Conditions||Strain Background||Reference|