Mode of action of the TyrR protein: repression and activation of the tyrP promoter of Escherichia coli
Open Access
- 13 February 2004
- journal article
- Published by Wiley in Molecular Microbiology
- Vol. 52 (1), 243-256
- https://doi.org/10.1111/j.1365-2958.2003.03965.x
Abstract
The tyrP gene of Escherichia coli encodes a tyrosine specific transporter. Its synthesis is repressed by tyrosine but is activated by phenylalanine and to a lesser extent by tryptophan. Both of these effects are mediated by the TyrR protein when it binds to one or both of its cognate binding sites (TyrR boxes) which encompass nucleotides − 30 to − 75. Activation in the presence of phenylalanine or tryptophan involves a dimer binding to the upstream box and interacting with the α subunit (αCTD) of RNA polymerase (RNAP). Repression in the presence of tyrosine involves a hexamer binding to both TyrR boxes. The molecular basis for this repression has been studied in vitro. Whereas initial gel shift experiments fail to show the exclusion of RNAP from the promoter region when TyrR hexamer is bound, a DNase I analysis of slices from the gel shows that in the presence of TyrR, RNAP now binds to a previously unrecognized upstream promoter. Although this upstream promoter is bound strongly by RNAP and forms an open complex on linear DNA templates, it fails to form an open complex on supercoiled templates in vitro and is unable to initiate transcription in vivo. A subsequent gel shift assay using a tyrP fragment which eliminates the upstream RNAP binding site confirms conclusively that, in the presence of tyrosine and ATP, the TyrR protein prevents RNAP from binding to the tyrP promoter. In vitro studies have also been carried out in the presence of TyrR protein and phenylalanine. Binding of TyrR protein to the upstream TyrR box in the presence of phenylalanine is shown to increase the affinity of RNAP for the promoter and stimulate open complex formation at the − 10 region of the tyrP promoter. This observation coupled with the results from mutational analysis supports the proposal that TyrR‐phenylalanine activates tyrP transcription by stimulating the onset of open complex formation.Keywords
This publication has 43 references indexed in Scilit:
- The Central Domain of Escherichia coli TyrR Is Responsible for Hexamerization Associated with Tyrosine-mediated Repression of Gene ExpressionPublished by Elsevier ,2002
- FIS Modulates the Kinetics of Successive Interactions of RNA Polymerase with the Core and Upstream Regions of the tyrT PromoterJournal of Molecular Biology, 2002
- The bacterial DNA-binding protein H-NS represses ribosomal RNA transcription by trapping RNA polymerase in the initiation complexJournal of Molecular Biology, 2000
- Transcriptional activation by recruitmentNature, 1997
- DNA-bend modulation in a repressor-to-activator switching mechanismNature, 1995
- Ligand-induced Self-association of the Escherichia coli Regulatory Protein TyrRJournal of Molecular Biology, 1994
- TyrR protein of Escherichia coli and its role as repressor and activatorMolecular Microbiology, 1991
- Synergy between Escherichia coli CAP protein and RNA polymerase in the lac promoter open complexJournal of Molecular Biology, 1989
- Stringent control of bacterial transcriptionCell, 1985
- Sur la biosynthese de la β-galactosidase (lactase) chez Escherichia coli. La specificite de l'inductionBiochimica et Biophysica Acta, 1951