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Eukaryotic Cell doi:10.1128/EC.00414-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The role of PUG1 in inducible porphyrin and heme transport in Saccharomyces cerevisiae

Genetics and Metabolism Section, Liver Diseases Branch, NIDDK, National Institutes of Health, Bldg 10 Rm 9B-16, Bethesda, Maryland 20892, USA

^* To whom correspondence should be addressed. Email: carolinep{at}intra.niddk.nih.gov.

	Abstract

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 ⁵⁵Fe-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.