Saccharomyces cerevisiae 4 article 4 5 aminolevulinate synthase 2 5-Aminolevulinate Synthetase 2 5-aminolevulinate dehydratase 2 5-aminolevulinate synthase 2 Cytochromes 2 Enzyme Repression 2 Fungi 2 HEM R+ mutants 2 Hydroxymethylbilane Synthase 2 Mutation 2 Porphobilinogen Synthase 2 Porphyrins 2 Saccharomyces cerevisiae HEM R+ mutants 2 Spectrophotometry 2 Support, Non-U.S. Gov't 2 Uroporphyrinogen Decarboxylase 2 biosynthesis 2 catabolite repression 2 catabolite repression and de-repression 2 catabolite repression and derepression 2 fungus mutant 2 heme 2 heme biosynthesis 2 heme synthesis 2 intracellular 5-aminolevulinate acid 2 metabolic regulation 2 mutant 2 nonhuman 2