title: Regulation of the steroid-inducible 3alpha-hydroxysteroid dehydrogenase/carbonyl reductase gene in Comamonas testosteroni.
abstract: The Comamonas testosteroni 3alpha-hydroxysteroid dehydrogenase/carbonyl reductase gene (hsdA) codes for an adaptive enzyme in the degradation of steroid compounds. However, no information was available on the molecular regulation of steroid-inducible genes nor on the mechanism of steroid signaling in procaryotes. We, therefore, investigated the cis- and trans-acting elements of hsdA expression to infer the mechanism of its molecular regulation by steroids. The gene was localized on a 5.257-kilobase EcoRI fragment of C. testosteroni chromosomal DNA. The promoter was characterized, and the transcriptional start site was identified. Two palindromic operator domains were found upstream of hsdA. A new gene coding for a trans-acting negative regulator (repressor A, RepA) of hsdA expression was characterized. The specific interaction between RepA, testosterone, and the operator domain is demonstrated. From our results we conclude that hsdA is under negative transcriptional control by an adjacent gene product (RepA). Accordingly, induction of hsdA by steroids in fact is a derepression, where steroidal inducers bind to the repressor, thereby preventing its binding to the hsdA operator.
authors.affiliation: Department of Pharmacology and Toxicology, School of Medicine, Philipps University of Marburg, Karl-von-Frisch-Strasse 1, D-35033 Marburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Xiong
authors.forename: E
authors.initials: E
authors.lastname: Maser
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D003001:Cloning, Molecular; D020604:Comamonas testosteroni / Q000201:enzymology*; D004247:DNA / Q000378:metabolism; D004265:DNA Helicases; D004268:DNA-Binding Proteins; D004797:Enzyme-Linked Immunosorbent Assay; D016368:Frameshift Mutation; D017353:Gene Deletion; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D006913:Hydroxysteroid Dehydrogenases / Q000235:genetics* / Q000378:metabolism*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D015719:Single-Strand Specific DNA and RNA Endonucleases / Q000378:metabolism; D013739:Testosterone / Q000378:metabolism; D015534:Trans-Activators; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D011506:Proteins; D015534:Trans-Activators; C045264:replication initiator protein; D013739:Testosterone; D004247:DNA; C425306:3alpha-hydroxysteroid dehydrogenase-carbonyl reductase; D000429:Alcohol Oxidoreductases; D006913:Hydroxysteroid Dehydrogenases; D015500:Chloramphenicol O-Acetyltransferase; D015719:Single-Strand Specific DNA and RNA Endonucleases; D004265:DNA Helicases