title: Transcriptional activation of the bkd operon of Pseudomonas putida by BkdR.
abstract: Reinvestigation of the transcriptional start site of the bkd operon of Pseudomonas putida revealed that the transcriptional start site was located 86 nucleotides upstream of the translational start. There was a sigma 70 binding site 10 bp upstream of the transcriptional start site. The dissociation constants for BkdR, the transcriptional activator of the bkd operon, were 3.1 x 10(-7) M in the absence of L-valine and 8.9 x 10(-8) M in the presence of L-valine. Binding of BkdR to substrate DNA in the absence of L-valine imposed a bend angle of 92 degrees in the DNA. In the presence of L-valine, the angle was 76 degrees. BkdR did not bind to either of the two fragments of substrate DNA resulting from digestion with AgeI. Because AgeI attacks between three potential BkdR binding sites, this suggests that binding of BkdR is cooperative. P. putida JS110 and JS112, mutant strains which do not express any of the components of branched-chain keto acid dehydrogenase, were found to contain missense mutations in bkdR resulting in R40Q and T22I changes in the putative helix-turn-helix of BkdR. Addition of glucose to the medium repressed expression of lacZ from a chromosomal bkdR-lacZ fusion, suggesting that catabolite repression of the bkd operon was the result of reduced expression of bkdR. These data are used to present a model for the role of BkdR in transcriptional control of the bkd operon.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City 73190, USA.
authors.forename: K T
authors.initials: KT
authors.lastname: Madhusudhan
authors.forename: K L
authors.initials: KL
authors.lastname: Hester
authors.forename: V
authors.initials: V
authors.lastname: Friend
authors.forename: J R
authors.initials: JR
authors.lastname: Sokatch
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D003470:Culture Media; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism; D019077:Helix-Turn-Helix Motifs / Q000235:genetics; D007658:Ketone Oxidoreductases / Q000235:genetics*; D051756:Leucine-Responsive Regulatory Protein; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics*; D009154:Mutation; D009690:Nucleic Acid Conformation; D009876:Operon; D016958:Pseudomonas putida / Q000201:enzymology / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D009097:Multienzyme Complexes; D014157:Transcription Factors; D051756:Leucine-Responsive Regulatory Protein; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D005947:Glucose