Enzyme Repression Mutation 4 catabolite repression 4 5 aminolevulinate synthase 2 5-Aminolevulinate Synthetase 2 Chloramphenicol 2 Cytochromes 2 Escherichia coli 2 Fungi 2 Galactosidases 2 Hydroxymethylbilane Synthase 2 Porphobilinogen Synthase 2 Porphyrins 2 RNA, Bacterial 2 RNA, Messenger 2 Saccharomyces cerevisiae 2 Saccharomyces cerevisiae HEM R+ mutants 2 Spectrophotometry 2 Support, Non-U.S. Gov't 2 Transcription, Genetic 2 Translation, Genetic 2 Uroporphyrinogen Decarboxylase 2 article 2 biosynthesis 2 catabolite repression and derepression 2 escherichia coli 2 fungus mutant 2 in vitro study 2 lactose 2 messenger rna 2