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At least 775 records · Page 43Linked to original sources
PubMed1978

Molecular events during the release of delta-aminolevulinate dehydratase from catabolite repression.

Transfer of exponential-phase cells of Saccharomyces cerevisiae, previously grown in 2% glucose, to a derepression medium resulted in a prompt increase in the level of delta-aminolevulinate dehydratase, the rate-limiting enzyme of heme biosynthesis under these conditions. This derepression exhibited a lag of 35 min at 23 degrees C and required the participation of both RNA and protein syntheses. Dissection of the molecular events during this lag period disclosed that RNA synthesis, rnal gene function (messenger RNA transport from nucleus to cytosol), and initiation of protein synthesis were completed within less than 10, 18, and 24 min, respectively. The potential regulation of derepression by mitochondrial gene products and mitochondrial function was probed by means of a series of isogenic, respiration-deficient (rho-, pet-, and mit-) mutants; no such regulation was found.

Enzyme Repression↗
PubMed1982

Regulation of amidase formation in mutants from Pseudomonas aeruginosa PAO lacking glutamine synthetase activity.

The formation of amidase was studied in mutants from Pseudomonas aeruginosa PAO lacking glutamine synthetase activity. It appeared that catabolite repression of amidase synthesis by succinate was partially relieved when cellular growth was limited by glutamine. Under these conditions, a correlation between amidase and urease formation was observed. The results suggest that amidase formation in strain PAO is subject to nitrogen control and that glutamine or some compound derived from it mediates the nitrogen repression of amidase.

Amidohydrolases↗
PubMed1975

Ammonium uptake by nitrogen fixing bacteria I. Azotobacter vinelandii.

Both the changes in the activities of nitrogenase, glutamine synthetase and glutamate dehydrogenase and in the extracellular and intracellular NH4+ concentrations were investigated during the transition from an NH4+ free medium to one containing NH4+ ions for a continuous culture of Azotobacter vinelandii. If added in amounts causing 80-100% repression of nitrogenase, ammonium acetate, lactate and phosphate are absorbed completely, whereas chloride, sulfate and citrate are only taken up to about 80%. After about 1-2 hrs the NH4+ remaining in the medium is absorbed too, indicating the induction or activation of a new NH4+ transport system. One of the new permeases allows the uptake of citrate in the presence of sucrose. Addition of inorganic NH4+ level leads to a reversible rise in the glutamine synthetase activity which is not prevented by chloramphenicol, and to a reversible decrease in nitrogenase activity. During these measurements glutamate dehydrogenase activity remains close to zero. The intracellular NH4+ level of about 0.6 mM does not change when extracellular NH4+ is taken up and repression of nitrogenase starts.

Acetates↗
PubMed1989

Role of transcriptional interference in the Drosophila melanogaster Adh promoter switch.

The Drosophilia melanogaster alcohol dehydrogenase (Adh) gene is transcribed from two closely linked promoters, which are regulated by two upstream enhancers. The proximal promoter is active primarily in first to early third-instar larvae, whereas the distal promoter is active in late third-instar larvae and adults. The Adh larval enhancer and the proximal promoter are separated by the Adh adult enhancer and the distal promoter. Because the proximal promoter is turned off just as the distal promoter is turned on, we considered the possibility that the distal promoter or adult enhancer has a role in the downregulation of the proximal promoter. We report here that transcription from the distal promoter is required to shut off the proximal promoter. In the absence of the distal promoter, the proximal promoter is active throughout larval development and in adults. The proximal promoter is also aberrantly active in adults when placed upstream of the distal promoter. These results suggest that the developmental switch from proximal to distal promoter is regulated by the stage-specific activation of the distal promoter, and the subsequent repression of the proximal promoter by transcriptional interference.

Alcohol Dehydrogenase↗
PubMed1993

The glucose-6-phosphate-isomerase reaction is essential for normal glucose repression in Saccharomyces cerevisiae.

Wild-type Saccharomyces cerevisiae and a strain carrying a deletion in the glucose-6-phosphate-isomerase gene (pgi1) were grown in carbon-limited continuous cultures on a mixture of fructose and galactose. Pulses of glucose, fructose and galactose were given to these cultures to investigate whether the pgi1 strain was capable of normal glucose repression. Glucose and galactose pulses inhibited fructose consumption and thus glycolysis in the pgi1 strain by a combination of competition between glucose and fructose at the uptake and/or phosphorylation level and inhibition of fructose uptake and/or phosphorylation by glucose 6-phosphate. Fructose pulses administered to the pgi1 strain transiently decreased the glycolytic flux downstream of fructose-1,6-bisphosphate. Transcriptional induction of the PDC1 gene (encoding pyruvate decarboxylase) was observed after glucose or galactose pulses were applied to the pgi1 strain, demonstrating that metabolism of these sugars beyond glucose 6-phosphate is dispensable for PDC1 induction. Fructose also induced PDC1 transcription, indicating that intracellular sugars could act as trigger for PDC1 induction or, alternatively, that two inductors are present. In contrast to the wild-type transcriptional inhibition of the glucose-repressible genes, HXK1 and GAL10 (encoding hexokinase isoenzyme 1 and uridine diphosphoglucose-4-epimerase, respectively) did not occur upon addition of glucose or fructose to the pgi1 mutant. Transcriptional repression was observed after application of the fructose pulse when the yeast had resumed metabolism of fructose. These results demonstrate that the initial signal for catabolite repression is not generated by high sugar concentrations or high concentrations of intermediates; moreover a simple role for the hexokinases can also be excluded. The absence of an increased glycolytic flux in the pgi1 mutant after administration of the sugar pulses while the concentrations of sugar and glycolytic intermediates were high, suggests that the initial signal for glucose repression could be linked to an increased glycolytic flux. The occurrence of PDC1 induction in the pgi1 strain while GAL10/HXKI repression is absent, demonstrates that the initial signals for catabolite induction and catabolite repression are different.

Blotting, Northern↗
PubMed1967

Catabolite repression and pyruvate metabolism in Escherichia coli.

A study was made of the reactions involved in the cellular regulatory function known as catabolite repression. These studies employed the glucose-repressible, beta-galactosidase system of Escherichia coli and involved an investigation of glucose dissimilation under cultural conditions capable of permitting or preventing expression of catabolite repression. The results indicated that reactions associated with pyruvate decarboxylation are of particular importance in influencing repression. This conclusion was based on results obtained by measurement of differential rates of C(14)O(2) evolution from specifically labeled (14)C-glucose substrates, and by measurements of H(2) evolution during anaerobic growth. Catabolite repression measured in relation to steady-state growth rates indicated that the repression mechanism may in fact be a direct consequence of a cell's energy balance, as dictated by the production from pyruvate of "high-energy" molecules such as adenosine triphosphate or acetyl-coenzyme A. The apparent involvement of pyruvate metabolism in both the energetics and the expression of catabolite repression in E. coli is consistent with this view.

Carbon Isotopes↗
PubMed1989

Upstream regulatory sequences of the yeast RNR2 gene include a repression sequence and an activation site that binds the RAP1 protein.

The small subunit of ribonucleotide reductase in Saccharomyces cerevisiae (RNR2) was induced 3- to 20-fold by a variety of DNA-damaging agents. Induction of the RNR2 transcript by at least one of these agents, methyl methanesulfonate, did not require protein synthesis. To identify sequences involved in the regulation of RNR2, we introduced deletions upstream of the transcription start site. Sequences required for induction were contained within a 200-base-pair region that could confer methyl methanesulfonate inducibility on the heterologous CYC1 promoter. This region contained a repression sequence and at least two positive activation sites. One of these activation sites bound RAP1, a protein known to associate with mating-type silencers and the upstream activation sequences of a number of genes. The behavior of deletions of the repression sequence suggests that induction of RNR2 may occur, at least in part, through relief of repression.

Base Sequence↗
PubMed1964

PRODUCTION OF PENICILLIN ACYLASE.

The production of penicillin acylase by Escherichia coli Ny.I/3-67 has been increased by phenylacetic acid and phenoxyacetic acid, which themselves strongly inhibit the function of this specific enzyme. Other carbonic acids also increased penicillin acylase production, but to a lesser degree; they also weakly inhibited enzyme function. The production of this enzyme was effectively repressed with metabolic carbohydrates and polyalcohols. Because enzyme production is dependent upon temperature, an increase in the temperature of incubation (above 31 C) decreased production of the enzyme, and increased the repressive effect of carbohydrates and polyalcohols.

Acetates↗
PubMed2005

Steady-state analysis of glucose repression reveals hierarchical expression of proteins under Mig1p control in Saccharomyces cerevisiae.

Glucose repression is a global transcriptional regulatory mechanism commonly observed in micro-organisms for the repression of enzymes that are not essential for glucose metabolism. In Saccharomyces cerevisiae, Mig1p, a homologue of Wilms' tumour protein, is a global repressor protein dedicated to glucose repression. Mig1p represses genes either by binding directly to the upstream repression sequence of structural genes or by indirectly repressing a transcriptional activator, such as Gal4p. In addition, some genes are repressed by both of the above mechanisms. This raises a fundamental question regarding the physiological relevance of the varied mechanisms of repression that exist involving Mig1p. We address this issue by comparing two well-known glucose-repression systems, that is, SUC2 and GAL gene expression systems, which encompass all the above three mechanisms. We demonstrate using steady-state analysis that these mechanisms lead to a hierarchical glucose repression profile of different family of genes. This switch over from one carbon source to another is well-calibrated as a function of glucose concentration through this hierarchical transcriptional response. The mechanisms prevailing in this repression system can achieve amplification and sensitivity, as observed in the well-characterized MAPK (mitogen-activated protein kinase) cascade system, albeit through a different structure. A critical feature of repression predicted by our steady-state model for the mutant strain of S. cerevisiae lacking Gal80p agrees well with the data reported here as well as that available in the literature.

DNA-Binding Proteins↗
PubMed1980

Regulatory control of 3-deoxy-D-arabino-heptulosonic acid 7-phosphate synthetase in Streptomyces antibioticus.

Streptomyces antibioticus possesses a tryptophan-inhibitable 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) synthetase whose synthesis is also repressed by L-tryptophan. Studies of the DAHP synthetase obtained by ammonium sulfate fractionation of a crude extract derived from S. Antibioticus revealed that the enzymic activity was only partially inhibited by tryptophan. Inhibition of the DAHP synthetase activity was strongly pH dependent at values below 7.0. A number of tryptophan analogues was noted to inhibit the enzyme; by contrast, other aromatic amino acid end products failed to affect DAHP synthetase activity. Chorismic acid, a key intermediate in aromatic amino acid biosynthesis, was ineffective as an inhibitor when used alone; however, if supplied with L-tryptophan, a further reduction of DAHP synthetase activity (15--25%) was routinely observed.

3-Deoxy-7-Phosphoheptulonate Synthase↗