PMID:8230210
| Citation |
Egan, SM and Schleif, RF (1993) A regulatory cascade in the induction of rhaBAD. J. Mol. Biol. 234:87-98 |
|---|---|
| Abstract |
The RhaS and RhaR regulatory proteins are encoded in the Escherichia coli L-rhamnose gene cluster. We used complementation analysis and DNA mobility shift assays to show that RhaR is not the direct activator of the L-rhamnose catabolic operon, rhaBAD. An in-frame deletion of rhaS (rhaS-rhaR+) eliminated expression from the rhaBAD promoter, pBAD, while overexpression of rhaS greatly speeded the normally slow induction of transcription from pBAD. Expression from pBAD in a coupled transcription-translation assay was only detected when rhaS+ DNA was added to allow synthesis of RhaS protein. RhaS thus appears to be the direct L-rhamnose-specific activator of rhaBAD expression. Deletion mapping located the binding site for the L-rhamnose-specific regulator to a region overlapping position -70 relative to the rhaBAD transcription start site. Deletion mapping and DNA mobility shift assays located a CRP binding site just upstream from the binding site for the L-rhamnose-specific regulator. Quantitative primer extension analysis showed that induction of both the rhaBAD and rhaSR messages was unusually slow, requiring 40 to 50 minutes to reach a steady-state level. Induction of rhaBAD apparently involves a regulatory cascade in which RhaR first induces rhaSR expression, then RhaS accumulates and induces rhaBAD expression. |
| Links |
PubMed Online version:10.1006/jmbi.1993.1565 |
| Keywords |
Bacterial Proteins/physiology; Base Sequence; Carrier Proteins; Cyclic AMP Receptor Protein/metabolism; DNA Primers/chemistry; DNA, Bacterial/genetics; DNA-Binding Proteins/metabolism; DNA-Binding Proteins/physiology; Escherichia coli Proteins; Gene Expression Regulation, Bacterial; Genes, Bacterial; Genes, Regulator; Molecular Sequence Data; Operon; Promoter Regions, Genetic; Rhamnose/metabolism; Trans-Activators; Transcription Factors/physiology; Transcription, Genetic |
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