Repression and activation of promoter-bound RNA polymerase activity by GAL repressor

Choy, Hyon E.; Hanger, Robert R.; Aki, Tsunehiro; Mahoney, Michael; Murakami, Katsuhiko; Ishihama, A

doi:10.1006/jmbi.1997.1516

Cited by 15 publications

(18 citation statements)

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“…The promoters are repressed by GalR by two different mechanisms. Either (i) GalR represses P1 by inhibiting open complex formation at the promoter-bound RNA polymerase (33) or (ii) P2 is repressed by a DNA loop that makes the promoter inadequate for transcription initiation (10,11). The presence of D-galactose inactivates GalR to release the repression in each case (25).…”

Section: Resultsmentioning

confidence: 99%

Induction of the Galactose Enzymes in Escherichia coli Is Independent of the C-1-Hydroxyl Optical Configuration of the Inducer d -Galactose

Lee

Lewis

2008

J Bacteriol

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The two optical forms of aldohexose galactose differing at the C-1 position, ␣-D-galactose and ␤-D-galactose, are widespread in nature. The two anomers also occur in di-and polysaccharides, as well as in glycoconjugates. The anomeric form of D-galactose, when present in complex carbohydrates, e.g., cell wall, glycoproteins, and glycolipids, is specific. Their interconversion occurs as monomers and is effected by the enzyme mutarotase (aldose-1-epimerase). Mutarotase and other D-galactose-metabolizing enzymes are coded by genes that constitute an operon in Escherichia coli. The operon is repressed by the repressor GalR and induced by D-galactose. Since, depending on the carbon source during growth, the cell can make only one of the two anomers of D-galactose, the cell must also convert one anomer to the other for use in specific biosynthetic pathways. Thus, it is imperative that induction of the gal operon, specifically the mutarotase, be achievable by either anomer of D-galactose. Here we report in vivo and in vitro experiments showing that both ␣-D-galactose and ␤-D-galactose are capable of inducing transcription of the gal operon with equal efficiency and kinetics. Whereas all substitutions at the C-1 position in the ␣ configuration inactivate the induction capacity of the sugar, the effect of substitutions in the ␤ configuration varies depending upon the nature of the substitution; methyl and phenyl derivatives induce weakly, but the glucosyl derivative does not.D-Galactose, also known as cerebrose, is a natural aldohexose which is ubiquitous in bacteria, plants, and animals, including human brains (28). It occurs also as part of more complex carbohydrates, e.g., oligo-and polysaccharides, glycoproteins, and glycolipids, and as components of bacterial cell walls. DGalactose has two anomeric forms, ␣-D-galactopyranose and ␤-D-galactopyranose ( Fig. 1) (36). Although the anomers spontaneously interconvert slowly in aqueous solution, an enzyme (mutarotase or aldose-1-epimerase) is responsible for interconverting the two optical varieties in monosaccharide forms in vivo (6,21). Mutarotases are present throughout the prokaryotic and eukaryotic phyla (6,31,34,37). Mutarotase syntheses are also induced in response to specific signals. For example, galactose mutarotase synthesis is induced by retinoic acid in human myeloid cells (30). In the bacterium Escherichia coli, enzymes of D-galactose metabolism (15,20), including the mutarotase (6), are encoded in an operon which is induced by D-galactose. It has been suggested previously that only ␤-Dgalactose is the inducer of the gal operon (7). Since D-galactose moieties in complex carbohydrates are anomerically specific, ␣ or ␤, we hypothesize that the mutarotase enzyme, which interconverts the ␣ and ␤ anomers, must be induced for the interconversion when either one of the two anomers is present in the cell, say, by hydrolysis of D-lactose, which generates ␤-Dgalactose, or of D-melibiose, which generates ␣-D-galactose. In this study, we showed by both in vivo and in vitr...

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Section: Resultsmentioning

confidence: 99%

Induction of the Galactose Enzymes in Escherichia coli Is Independent of the C-1-Hydroxyl Optical Configuration of the Inducer d -Galactose

Lee

Lewis

2008

J Bacteriol

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“…8). We note that in 70 systems, repressor action at a step following promoter binding of RNAP requires a specific separate repressor protein (for review, see Choy et al 1997).…”

Section: Discussionmentioning

confidence: 99%

Amino-terminal sequences of sigma N (sigma 54) inhibit RNA polymerase isomerization

Cannon¹,

Gallegos²,

Casaz³

et al. 1999

Genes & Development

137

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In bacteria, association of the specialized N protein with the core RNA polymerase subunits forms a holoenzyme able to bind promoter DNA, but unable to melt DNA and initiate transcription unless acted on by an activator protein. The conserved amino-terminal 50 amino acids of N (Region I) are required for the response to activators. We have used pre-melted DNA templates, in which the template strand is unpaired and accessible for transcription initiation, to mimic a naturally melted promoter and explore the function of Region I. Our results indicate that one activity of Region I sequences is to inhibit productive interaction of holoenzyme with pre-melted DNA. On pre-melted DNA targets, either activation of N -holoenzyme or removal of Region I allowed efficient formation of complexes in which melted DNA was sequestered by RNA polymerase. Like natural pre-initiation complexes formed on conventional DNA templates through the action of activator, such complexes were heparin-resistant and transcriptionally active. The inhibitory N Region I domain functioned in trans to confer heparin sensitivity to complexes between Region I-deleted holoenzyme and pre-melted promoter DNA. Evidence that Region I senses the conformation of the promoter was obtained from protein footprint experiments. We suggest that one function for Region I is to mask a single-strand DNA-binding activity of the holoenzyme. On the basis of extended DNA footprints of Region I-deleted holoenzyme, we also propose that Region I prevents RNA polymerase isomerization, a conformational change necessary for access to and the subsequent stable association of holoenzyme with melted DNA.

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“…Some DNA-binding repressors stabilize initiating RNAP:promoter DNA complexes, thereby trapping RNAP at the promoter [45]. The nucleoid-associated protein, H-NS, can trap RNAP at promoters by forming looping interactions between binding sites upstream and downstream of the promoter [46].…”

Section: Regulating the Rate Of Transition By Proteins And Small Molementioning

confidence: 99%

The transition from transcriptional initiation to elongation

Wade

Struhl

2008

Current Opinion in Genetics & Development

102

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Transcription is the first step in gene expression, and its regulation underlies multicellular development and the response to environmental changes. Most studies of transcriptional regulation have focused on the recruitment of RNA polymerase to promoters. However, recent work has shown that, for many promoters, post-recruitment steps in transcriptional initiation are likely to be ratelimiting. The rate at which RNA polymerase transitions from transcriptional initiation to elongation varies dramatically between promoters and between organisms, and is the target of multiple regulatory proteins that can function to both repress and activate transcription.

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Repression and activation of promoter-bound RNA polymerase activity by GAL repressor

Cited by 15 publications

References 0 publications

Induction of the Galactose Enzymes in Escherichia coli Is Independent of the C-1-Hydroxyl Optical Configuration of the Inducer d -Galactose

Induction of the Galactose Enzymes in Escherichia coli Is Independent of the C-1-Hydroxyl Optical Configuration of the Inducer d -Galactose

Amino-terminal sequences of sigma N (sigma 54) inhibit RNA polymerase isomerization

The transition from transcriptional initiation to elongation

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