title: Mutations in the tyrR gene of Escherichia coli which affect TyrR-mediated activation but not TyrR-mediated repression.
abstract: Site-directed mutagenesis has been used to further characterize amino acid residues necessary for the activation of gene expression by the TyrR protein. Amino acid substitutions have been made at positions 2, 4, 5, 6, 7, 8, 9, 10, and 16. TyrR mutants with amino acid substitutions V-5-->P (VP5), VF5, CS7, CR7, DR9, RI10, RS10, and ER16 show no or very little activation of expression of either mtr or tyrP. In each case, however, the ability to repress aroF is unaltered. Amino acid substitutions at positions 4, 6, and 8 have no effect on activation. Small internal deletions of residues 10 to 19, 20 to 29, or 30 to 39 also destroy phenylalanine- or tyrosine-mediated activation of mtr and tyrP. In these mutants repression of aroF is also unaltered. In activation-defective tyrR mutants, expression of mtr is repressed in the presence of tyrosine. This tyrosine-mediated repression is trpR dependent and implies an interaction between TrpR and TyrR proteins in the presence of tyrosine.
authors.affiliation: Department of Microbiology, University of Melbourne, Parkville Victoria, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Yang
authors.forename: H
authors.initials: H
authors.lastname: Camakaris
authors.forename: A J
authors.initials: AJ
authors.lastname: Pittard
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018085:Regulon; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015183:Restriction Mapping; D017384:Sequence Deletion; D014157:Transcription Factors / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C069256:TyrR protein, E coli; D001616:beta-Galactosidase