PMID:2007555
| Citation |
Tokeson, JP, Garges, S and Adhya, S (1991) Further inducibility of a constitutive system: ultrainduction of the gal operon. J. Bacteriol. 173:2319-27 |
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| Abstract |
In wild-type Escherichia coli, expression of the gal operon is negatively regulated by the Gal repressor and is induced 10- to 15-fold when the repressor is inactivated by an inducer. In strains completely deleted for galR, the gene which encodes the Gal repressor, the operon is derepressed by only 10-fold without an inducer. But this derepression is increased further by threefold during cell growth in the presence of an inducer, D-galactose or D-fucose. This phenomenon of extreme induction in the absence of Gal repressor is termed ultrainduction--a manifestation of further inducibility in a constitutive setup. Construction and characterization of gene and operon fusion strains between galE and lacZ, encoding beta-galactosidase as a reporter gene, show that ultrainduction occurs at the level of transcription and not translation. Transcription of the operon, from both the cyclic AMP-dependent P1 and the cyclic nucleotide-independent P2 promoters, is subject to ultrainduction. The wild-type galR+ gene has an epistatic effect on ultrainducibility: ultrainduction is observed only in cells devoid of Gal repressor protein. Titration experiments show the existence of an ultrainducibility factor that acts like a repressor and functions by binding to DNA segments (operators) to which Gal repressor also binds to repress the operon. |
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| Keywords |
DNA Mutational Analysis; Enzyme Induction; Epistasis, Genetic; Escherichia coli/genetics; Escherichia coli Proteins; Galactokinase/genetics; Galactose; Gene Expression Regulation, Bacterial; Operator Regions, Genetic; Operon; Promoter Regions, Genetic; Protein Biosynthesis; Repressor Proteins/physiology; Transcription, Genetic |
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