Binding of the TorR regulator to cis-acting direct repeats activates tor operon expression.
Mol Microbiol
; 17(5): 971-80, 1995 Sep.
Article
in En
| MEDLINE
| ID: mdl-8596446
ABSTRACT
The expression of the Escherichia coli torCAD operon, which encodes the anaerobically expressed trimethylamine N-oxide (TMAO) reductase respiratory system, requires the presence of TMAO in the medium. The response regulator, TorR, has recently been identified as the regulatory protein that controls the expression of the torCAD operon in response to TMAO. The torC regulatory region contains four direct repeats of a decameric consensus motif designated the tor boxes. Alteration by base substitutions of any of the four tor boxes in a plasmid containing a torC'-lacZ fusion dramatically reduces TorR-dependent torC expression. In addition, deletion of the distal tor box (box1) abolishes torC induction whereas the presence of a DNA fragment starting three bases upstream from box1 suffices for normal torC expression. Footprinting and gel-retardation experiments unambiguously demonstrated that TorR binds to the torC regulatory region. Three distinct regions are protected by TorR binding. One of approximately 24 nucleotides covers the first two tor boxes (box1 and box2); the second is located upstream from the -35 promoter sequence and includes the third tor box (box3); the last is found downstream from the -35 sequence and corresponds to the fourth tor box (box4). Binding to the upstream tor boxes (box1 and box2) appears to be stronger than binding to the downstream tor boxes (box3 and box4) since only the upstream region is protected at the lower concentration of TorR used in the footprinting experiments. We propose a model in which multiple binding sites (i.e. the tor boxes) contribute to the formation of a nucleoprotein complex, but only one particular proximal site positions TorR properly so that it interacts with RNA polymerase.
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Collection:
01-internacional
Database:
MEDLINE
Main subject:
Operon
/
Oxidoreductases, N-Demethylating
/
Transcription Factors
/
Repetitive Sequences, Nucleic Acid
/
Gene Expression Regulation, Bacterial
/
Escherichia coli Proteins
/
Escherichia coli
Type of study:
Prognostic_studies
Language:
En
Journal:
Mol Microbiol
Journal subject:
BIOLOGIA MOLECULAR
/
MICROBIOLOGIA
Year:
1995
Document type:
Article
Affiliation country:
France