Dual control by purines and pyrimidines of the expression of the pyrD gene of Salmonella typhimurium.
Expression of the Salmonella typhimurium pyrD gene was found to be repressed two-fold when cells were grown in the presence of hypoxanthine. Purine-mediated repression was evident for reporter plasmids containing pyrD-lacZ transcriptional or translational fusions, indicating that regulation was being exercised at the level of transcriptional initiation. In a strain harbouring a purR6::Tn10 mutation inactivating the purine regulon repressor (PurR), expression of pyrD was not repressed by hypoxanthine. Gel retardation experiments provided evidence that PurR binds to a PUR box centered 27 base pairs upstream of the -35 region of the pyrD promoter. Site-directed mutagenesis was used to decrease the similarity of the putative PUR box to the consensus sequence; each mutation eliminated binding of PurR to the mutated DNA in vitro and abolished repression by hypoxanthine in purR+ cells in vivo. Regulation by pyrimidines was unaffected by either of the two PUR box mutations, showing that purine and pyrimidine control of pyrD expression can operate independently.
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Department of Chemistry, University of Regina, Saskatchewan, Canada.
Baker
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D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D004080:Dihydroorotase / Q000235:genetics; D000090722:Dihydroorotate Dehydrogenase; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010088:Oxidoreductases / Q000235:genetics; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011401:Promoter Regions, Genetic; D011687:Purines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D012097:Repressor Proteins / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D000090722:Dihydroorotate Dehydrogenase; C065825:PurR protein, Bacteria; D011687:Purines; D011743:Pyrimidines; D012097:Repressor Proteins; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D004080:Dihydroorotase; C030985:purine