title: On the mechanism by which alkaline pH prevents expression of an acid-expressed gene.
abstract: Previous work has shown that zinc finger transcription factor PacC mediates the regulation of gene expression by ambient pH in the fungus Aspergillus nidulans. This regulation ensures that the syntheses of molecules functioning in the external environment, such as permeases, secreted enzymes, and exported metabolites, are tailored to the pH of the growth environment. A direct role for PacC in activating the expression of an alkaline-expressed gene has previously been demonstrated, but the mechanism by which alkaline ambient pH prevents the expression of any eukaryotic acid-expressed gene has never been reported. Here we show that a double PacC binding site in the promoter of the acid-expressed gabA gene, encoding gamma-aminobutyrate (GABA) permease, overlaps the binding site for the transcriptional activator IntA, which mediates omega-amino acid induction. Using bacterially expressed fusion proteins, we have shown that PacC competes with IntA for DNA binding in vitro at this site. Thus, PacC repression of GABA permease synthesis is direct and occurs by blocking induction. A swap of IntA sites between promoters for gabA and amdS, a gene not subject to pH regulation, makes gabA expression pH independent and amdS acid expressed.
authors.affiliation: Department of Infectious Diseases, Imperial College School of Medicine at Hammersmith Hospital, London W12 0NN, United Kingdom.
authors.forename: E A
authors.initials: EA
authors.lastname: Espeso
authors.forename: H N
authors.initials: HN
authors.lastname: Arst
mesh_terms: D000468:Alkalies; D000581:Amidohydrolases / Q000235:genetics; D001233:Aspergillus nidulans / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D006863:Hydrogen-Ion Concentration; D026901:Membrane Transport Proteins / Q000235:genetics*; D016296:Mutagenesis; D027361:Organic Anion Transporters; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D000468:Alkalies; C079045:AmdR protein, Aspergillus nidulans; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C092394:PacC protein, Aspergillus; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D005680:gamma-Aminobutyric Acid; D000581:Amidohydrolases; C021445:acetamidase