title: Application of AgaR repressor and dominant repressor variants for verification of a gene cluster involved in N-acetylgalactosamine metabolism in Escherichia coli K-12.
abstract: The agaZVWEFASYBCDI gene cluster encodes the phosphotransferase systems and enzymes responsible for the uptake and metabolism of N-acetylgalactosamine and galactosamine in Escherichia coli. In some strains of E. coli, particularly the common K-12 strain, a portion of this cluster is missing because of a site-specific recombination event that occurred between sites in agaW and agaA. Strains that have undergone this recombination event have lost the ability to utilize either N-acetylgalactosamine or galactosamine as sole sources of carbon. Divergently transcribed from this gene cluster is the gene agaR encoding a transcriptional repressor belonging to the DeoR/GlpR family of transcriptional regulators. Promoters upstream of agaR, agaZ and agaS were characterized. All three promoters had elevated activity in the presence of N-acetylgalactosamine or galactosamine, were regulated in vivo by AgaR and possessed specific DNA-binding sites for AgaR upstream from the start sites of transcription as determined by DNase I footprinting. In vivo analysis and DNase I footprinting indicated that the promoter specific for agaZ also requires activation by cAMP-CRP. Previous work with GlpR and other members of the DeoR/GlpR family have identified highly conserved amino acid residues that function in DNA-binding or response to inducer. These residues of AgaR were targeted for site-directed mutagenesis and yielded variants of AgaR that were either negatively dominant or non-inducible. The apparent ability to produce negatively dominant and non-inducible variants of proteins of the DeoR/GlpR family of currently unknown function will likely facilitate screening for function.
authors.affiliation: Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
authors.forename: W Keith
authors.initials: WK
authors.lastname: Ray
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Larson
mesh_terms: D000116:Acetylgalactosamine / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins; D000242:Cyclic AMP / Q000378:metabolism; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism; D018983:DNA Footprinting; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005810:Multigene Family; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D000242:Cyclic AMP; D000116:Acetylgalactosamine