title: Activation of gene expression by a ligand-induced conformational change of a protein-DNA complex.
abstract: IlvY protein binds cooperatively to tandem operator sites in the divergent, overlapping, promoter-regulatory region of the ilvYC operon of Escherichia coli. IlvY positively regulates the expression of the ilvC gene in an inducer-dependent manner and negatively regulates the transcription of its own divergently transcribed structural gene in an inducer-independent manner. Although binding of IlvY protein to the tandem operators is sufficient to repress ilvY promoter-specific transcription, it is not sufficient to activate transcription from the ilvC promoter. Activation of ilvC promoter-specific transcription requires the additional binding of a small molecule inducer to the IlvY protein-DNA complex. The binding of inducer to IlvY protein does not affect the affinity of IlvY protein for the tandem operator sites. It does, however, cause a conformational change of the IlvY protein-DNA complex, which is correlated with the partial relief of an IlvY protein-induced bend of the DNA helix in the ilvC promoter region. This structural change in the IlvY protein-DNA complex results in a 100-fold increase in the affinity of RNA polymerase binding at the ilvC promoter site. The ability of a protein to regulate gene expression by ligand-responsive modulation of a protein-DNA structure is an emerging theme in gene regulation.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Irvine, California 92697, USA.
authors.forename: K Y
authors.initials: KY
authors.lastname: Rhee
authors.forename: D F
authors.initials: DF
authors.lastname: Senear
authors.forename: G W
authors.initials: GW
authors.lastname: Hatfield
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D004274:DNA, Recombinant / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D005786:Gene Expression Regulation; D008024:Ligands; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D013816:Thermodynamics
chemical_list: D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D008024:Ligands; D012321:DNA-Directed RNA Polymerases