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PubMed1975

Insensitivity of D-amino acid dehydrogenase synthesis to catabolic repression in dadR mutants of Salmonella typhimurium.

It has been found that synthesis of D-amino acid dehydrogenase in Salmonella typhimurium is stimulated by cyclic AMP and crp gene product. This indicates that catabolic control of the dehydrogenase resembles other bacterial systems of catabolic repression. We have isolated S. typhimurium mutants, dadR, which are resistant to L-methionine-interference with D-histidine utilization and are able to utilize D-tryptophan as a precursor of L-tryptophan. Mapping data indicate that the dadR locus is closely linked to dadA coding for the structure of D-amino acid dehydrogenase. The synthesis of the dehydrogenase in dadR mutants is completely insensitive to the repression by glucose, but remains inducible by L-alanine. We conclude thereof that dadR mutants have changes in the promoter region which increase the expression of the dadA gene in the presence of glucose metabolism. A likely possibility that induction of the dad operon by alanine might be under positive control is discussed.

Alanine↗
PubMed1987

Separate regulatory systems for the repression of metE and btuB by vitamin B12 in Escherichia coli.

Synthesis of the btuB-encoded outer membrane receptor for vitamin B12 and the metE-encoded homocysteine methyltransferase is repressed by growth of Escherichia coli in the presence of vitamin B12. The regulation by vitamin B12 of the production of beta-galactosidase in strains carrying btuB-lac or metE-lac operon fusions indicated that repression of both genes operates at the transcriptional level. Selection for expression of these fusions under repressive conditions allowed isolation of second-site mutations in which repressibility by vitamin B12 had been lost. Mutations in metH and metF prevented vitamin B12-dependent regulation of metE, but not that of btuB. Mutations in btuB and other genes involved in uptake of the vitamin eliminated or reduced repression. Mutations in the newly identified gene, btuR, controlled the repressibility of btuB, but had no effect on metE regulation. The btuR gene resides at 27.9 min on the genetic map in the gene order cysB-topA-btuR-trp; it acts in a trans-dominant manner and appears to encode a repressor of btuB transcription.

Bacterial Outer Membrane Proteins↗
PubMed1980

Regulation of nitrogenase biosynthesis in Klebsiella pneumoniae: effect of nitrate.

The rate of biosynthesis of nitrogenase polypeptides in Klebsiella pneumoniae was determined in a medium containing NaNO3 or NaNO2. Nitrogenase biosynthesis was completely repressed by NO3- in a mutant strain, strain SK-25, that is derepressed for nitrogenase biosynthesis in the presence of NH4+. Chlorate-resistant mutants, derived from strain SK-25, that are defective in NO3- respiration produced nitrogenase in the presence of NO3-. Strain SK-56), a chlorate-resistant derivative capable of NO3- respiration, produced no nitrogenase in the presence of NO3- or NO2-. Klebsiella pneumoniae respired under anaerobic conditions utilizing either NO3- or NO2- as terminal electron acceptor. A mechanism for the control of nitrogenase biosynthesis is discussed involving the redox control of anaerobic enzyme systems.

Anaerobiosis↗
PubMed1995

Two different mechanisms mediate catabolite repression of the Bacillus subtilis levanase operon.

There are two levels of control of the expression of the levanase operon in Bacillus subtilis: induction by fructose, which involves a positive regulator, LevR, and the fructose phosphotransferase system encoded by this operon (lev-PTS), and a global regulation, catabolite repression. The LevR activator interacts with its target, the upstream activating sequence (UAS), to stimulate the transcription of the E sigma L complex bound at the "-12, -24" promoter. Levanase operon expression in the presence of glucose was tested in strains carrying a ccpA gene disruption or a ptsH1 mutation in which Ser-46 of HPr is replaced by Ala. In a levR+ inducible genetic background, the expression of the levanase operon was partially resistant to catabolite repression in both mutants, indicating that the CcpA repressor and the HPr-SerP protein are involved in the glucose control of this operon. In addition, a cis-acting catabolite-responsive element (CRE) of the levanase operon was identified and investigated by site-directed mutagenesis. The CRE sequence TGAAAACGCTT(a)ACA is located between positions -50 and -36 from the transcriptional start site, between the UAS and the -12, -24 promoter. However, in a background constitutive for levanase, neither HPr, CcpA, nor CRE is involved in glucose repression, suggesting the existence of a different pathway of glucose regulation. Using truncated LevR proteins, we showed that this CcpA-independent pathway required the presence of the domain of LevR (amino acids 411 to 689) homologous to the BglG family of bacterial antiterminators.

Bacillus subtilis↗
PubMed1999

Repression of acyl-CoA:cholesterol acyltransferase by a traditional herbal medicine (Kampo medicine), Ogi-Keishi-Gomotsu-To-Ka-Kojin.

Ogi-Keishi-Gomotsu-To-Ka-Kojin (OKGK) is a traditional herbal medicine (Kampo medicine) which has been found to ameliorate hypercholesterolemia and hypertriglyceridemia in rats and rabbits. In the present study, the effect of OKGK on acyl-CoA:cholesterol acyltransferase (ACAT) was studied in order to elucidate the mechanism of its antihypercholesterolemic action. Oral administration of OKGK to rats fed a cholesterol-enriched diet for 4 weeks markedly repressed the increase in ACAT activity in the small intestine. In contrast, OKGK did not influence hepatic ACAT activity. These results indicate that OKGK selectively inhibits ACAT activity in the small intestine relative to that in the liver, resulting in a reduction of cholesterol absorption, followed by a decrease in serum cholesterol.

Adrenal Glands↗
PubMed1986

[Operon of riboflavin biosynthesis in Bacillus subtilis. XVII. A study of the regulatory functions of the intermediate products and their derivatives].

Repression of synthesis of GTP-cyclohydrolase and riboflavinsynthetase was studied in different regulatory mutants of Bacillus subtilis. The results of experiments with some riboflavin precursors and their derivatives revealed that 5-amino-2,6-dioxo-4-ribitylaminopyrimidine and 6-methyl-7-(1',2'-dioxyethyl)-8-ribityllumazine can serve as effectors in riboflavin biosynthesis.

Bacillus subtilis↗
PubMed1997

Regulation of synthesis of pyruvate carboxylase in the photosynthetic bacterium Rhodobacter capsulatus.

The synthesis of pyruvate carboxylase (PC) was studied by using quantitative immunoblot analysis with an antibody raised against PC purified from Rhodobacter capsulatus and was found to vary 20-fold depending on the growth conditions. The PC content was high in cells grown on pyruvate or on carbon substrates metabolized via pyruvate (lactate, D-malate, glucose, or fructose) and low in cells grown on tricarboxylic acid (TCA) cycle intermediates or substrates metabolized without intermediate formation of pyruvate (acetate or glutamate). Under dark aerobic growth conditions with lactate as a carbon source, the PC content was approximately twofold higher than that found under light anaerobic growth conditions. The results of incubation experiments demonstrate that PC synthesis is induced by pyruvate and repressed by TCA cycle intermediates, with negative control dominating over positive control. The content of PC in R. capsulatus cells was also directly related to the growth rate in continuous cultures. The analysis of intracellular levels of pyruvate and TCA cycle intermediates in cells grown under different conditions demonstrated that the content of PC is directly proportional to the ratio between pyruvate and C4 dicarboxylates. These results suggest that the regulation of PC synthesis by oxygen and its direct correlation with growth rate may reflect effects on the balance of intracellular pyruvate and C4 dicarboxylates. Thus, this important enzyme is potentially regulated both allosterically and at the level of synthesis.

Aerobiosis↗
PubMed2001

Evidence for two pathways of thiosulfate oxidation in Starkeya novella (formerly Thiobacillus novellus).

The pathway of thiosulfate oxidation in the facultatively chemolithotrophic, sulfur-oxidizing bacterium Starkeya novella (formerly Thiobacillus novellus) has not been established beyond doubt. Recently, isolation of the sorAB genes, which encode a soluble sulfite:cytochrome c oxidoreductase, has been reported, indicating that a thiosulfate-oxidizing pathway not involving a multienzyme complex may exist in this organism. Here we report the cloning and sequencing of the soxBCD genes from S. novella, which are closely related to the corresponding genes encoding the thiosulfate-oxidizing multienzyme complex from Paracoccus pantotrophus. These findings suggest two distinct pathways for thiosulfate oxidation in S. novella. The expression of sorAB and soxC in cells grown on thiosulfate- and/or glucose-containing media was studied by Western blot analysis. The results showed that the SorAB protein is synthesized in the presence of thiosulfate irrespective of the presence of glucose. In contrast, the SoxC protein is subject to repression by glucose; the repression, however, appears to be dependent on the relative amounts of glucose and thiosulfate present. The regulatory effects observed for the expression of sorAB are likely to be mediated by an extracytoplasmic function sigma factor encoded by the sigE gene identified upstream of sorAB.

Amino Acid Sequence↗
PubMed1983

Carbon catabolite repression of maltase synthesis in Saccharomyces carlsbergensis.

Carbon catabolite repression of maltase gene expression is brought about by the addition of glucose, resulting in a drastic inhibition of the induction of maltase. When added to induced cells, glucose leads to the inhibition of maltase synthesis within 30 min, which can be accounted for by the disappearance of hybridizable maltase RNA sequences. The loss of maltase-specific RNA due to catabolite repression can be traced to the combined effects of a 15-fold decrease in the rate of transcription of the maltase structural gene 15 to 20 min after the addition of glucose and a change in the half-life of maltase mRNA. However, the stability of maltase, once induced, is not affected by the addition of glucose.

Enzyme Repression↗
PubMed1969

Isolation of amino acid transport-negative mutants of Pseudomonas aeruginosa and cells with repressed transport activity.

Methods are described for the isolation of amino acid transport-negative mutants of Pseudomonas aeruginosa and for the preparation of cells with repressed, specific amino acid permeases. P. aeruginosa was resistant to high concentrations of the majority of the 53 amino acid analogues examined and was unaffected by low concentrations of any of them. Cells which had been grown in the presence of sublethal concentrations of the few analogues which were inhibitory were subsequently more resistant to the analogues. These cells were also defective in the transport of the corresponding amino acid, as the analogue caused repression of the synthesis of the specific amino acid permease. The cells with repressed transport activity rapidly regained their normal level of constitutive permease when grown in the absence of the analogue. Higher levels of the permeases were induced when these cells were grown in the presence of the appropriate amino acid. The possible mechanisms for the mode of regulation of amino acid permeases are discussed.

Amino Acids↗
PubMed1977

Interrelationship of carbohydrate metabolism and alkaline phosphatase synthesis in Bacillus licheniformis 749/c.

Membrane-bound alkaline phosphatase of Bacillus licheniformis 749/c is derepressed by glucose in complex and chemically defined media. In the presence of lactate, pyruvate, or succinate the synthesis is repressed. The lactate repression neither affects total protein synthesis nor inhibits penicillinase synthesis. Thus, carbon sources specifically influence alkaline phosphatase synthesis. Although variations in the inorganic phosphate content of the growth media directly affect alkaline phosphatase synthesis, the intracellular inorganic and total phosphate pools appear to be unrelated to its repression or derepression. During lactate repression there is preferential incorporation of lactate molecules into glycogen, whereas no such incorporation could be detected from glucose. Net glycogen synthesis remains the same in glucose- or lactate-grown cells. It is postulated that, in phosphate-deficient growth medium, gluconeogenic metabolism regulates alkaline phosphatase synthesis.

Alkaline Phosphatase↗
PubMed2001

A novel function of 20-hydroxyecdysone: translational repression of the lysosomal protease mRNA in the mosquito fat body.

In the female fat body of the mosquito Aedes aegypti, lysosomes play important roles during the cessation of vitellogenesis by degrading the biosynthetic machinery and aiding the remodeling of the fat body cells. A detailed study of a mosquito lysosomal aspartic protease (AaLAP) has shown a unique expression pattern in the vitellogenic fat body: the level of AaLAP mRNA dramatically rises and peaks at 24 h post blood meal (PBM) correlating with the high titer of ecdysteroids; however, there is a 12 h lag before peak levels of AaLAP protein and its enzymatic activity has been observed. These observations suggest that the high titer of 20-hydroxyecdysone (20E) may hinder translation of the AaLAP mRNA. Here, we used an in vitro organ culture to study the effect of 20E on the protein synthesis of AaLAP in the fat body. The increase in the AaLAP protein level in the fat body, dissected at 24 h PBM and incubated for 6 or 12 h, was inhibited by the presence of 10(-5) M 20E in the medium. Incubation in the hormone-free medium did not effect accumulation of the AaLAP protein which proceeded at the levels comparable to the intact insect. Furthermore, the effect of 10(-5) M 20E on the AaLAP accumulation was reversible. These experiments support the hypothesis of the 20E-mediated repression of lysosomal protease mRNAs at the translational level in the regulation of vitellogenic and postvitellogenic events in the mosquito fat body. Analysis of the 5' and 3' -end untranslated regions (UTR) of AaLAP mRNA form secondary structures suggest that they may also contribute to mRNA stability and 20E-mediated translational inhibition.

Aedes↗
PubMed1984

Cellulase biosynthesis in a catabolite repression-resistant mutant of Thermomonospora curvata.

A catabolite repression-resistant mutant of the thermophilic actinomycete Thermomonospora curvata was obtained by treatment with ethyl methanesulfonate and UV light. Cellulase biosynthesis was undiminished by glucose, 2-deoxyglucose, or alpha-methyl glucoside, which are potent repressors in the wild type. Intracellular cyclic AMP levels were higher in the mutant in both the absence and the presence of repressors.

Cellulase↗
PubMed1990

Glucose-induced hyperaccumulation of cyclic AMP and defective glucose repression in yeast strains with reduced activity of cyclic AMP-dependent protein kinase.

Addition of glucose or related fermentable sugars to derepressed cells of the yeast Saccharomyces cerevisiae triggers a RAS-mediated cyclic AMP (cAMP) signal that induces a protein phosphorylation cascade. In yeast mutants (tpk1w1, tpk2w1, and tpk3w1) containing reduced activity of cAMP-dependent protein kinase, fermentable sugars, as opposed to nonfermentable carbon sources, induced a permanent hyperaccumulation of cAMP. This finding confirms previous conclusions that fermentable sugars are specific stimulators of cAMP synthesis in yeast cells. Despite the huge cAMP levels present in these mutants, deletion of the gene (BCY1) coding for the regulatory subunit of cAMP-dependent protein kinase severely reduced hyperaccumulation of cAMP. Glucose-induced hyperaccumulation of cAMP was also observed in exponential-phase glucose-grown cells of the tpklw1 and tpk2w1 strains but not the tpk3w1 strain even though addition of glucose to glucose-repressed wild-type cells did not induce a cAMP signal. Investigation of mitochondrial respiration by in vivo 31P nuclear magnetic resonance spectroscopy showed the tpk1w1 and tpk2w1 strains, to be defective in glucose repression. These results are consistent with the idea that the signal transmission pathway from glucose to adenyl cyclase contains a glucose-repressible protein. They also show that a certain level of cAMP-dependent protein phosphorylation is required for glucose repression. Investigation of the glucose-induced cAMP signal and glucose-induced activation of trehalase in derepressed cells of strains containing only one of the wild-type TPK genes indicates that the transient nature of the cAMP signal is due to feedback inhibition by cAMP-dependent protein kinase.

Adenosine Triphosphate↗
PubMed1970

Conversion of glycogen phosphorylase b to a by non-activated phosphorylase b kinase: an in vitro model of the mechanism of increase in phosphorylase a activity with muscle contraction.

Phosphorylase b kinase activity, as present in resting muscle in the non-activated form, appears to be ample to account for the fast appearance of phosphorylase a observed with muscle contraction. The kinase activity is repressed by free ATP and stimulated by free Mg(2+). Phosphorylase b kinase activity increases greatly when the Mg(2+):ATP ration exceeds 1. It is proposed that the breakdown of ATP that occurs during muscle contraction may represent the triggering factor for the observed in vivo conversion of phosphorylase b into a.

Adenosine Triphosphate↗
PubMed1971

Structural effects on Arthrobacter methylene hydroxylase activity.

Arthrobacter 4-44-2 (ATCC 25581), capable of subterminal oxidation of n-hexadecane to 2-, 3-, and 4-alcoholic and ketonic products, was examined for the ability of this methylene hydroxylase capability to be induced and repressed and for structural relationships influencing methylene function oxidation. Induction was best carried out by use of n-alkanes from 10 to 16 carbons in length and was especially strong with methylcyclohexane among cyclic compounds tested. Induction was not observed with several related alcohols, 1-unsaturated compounds, or methoxy and ethoxy compounds tested. After induction, n-alkanes 14 and 16 carbons in length were transformed to the corresponding internal oxidation products; however, no activity was observed with even-carbon alkanes of shorter chain length. Hexadecene-1 and all alcohols tested, including cyclododecanol, were transformed to corresponding ketonic or aldehydic products. Cyclic compounds tested, including cyclododecane, were not oxidized by induced cells, suggesting that a methyl group plays a role in orientation of the substrate for the methylene hydroxylation but that the methyl function was not as critical after completion of the hydroxylation step regardless of structural configuration. Acetate strongly repressed induction of n-hexadecane methylene hydroxylase activity. Inducibility of methylene hydroxylase activity was confirmed by use of cell-free systems with methylcyclohexane as an inducer. A stimulation of methylene hydroxylase activity by addition of reduced pyridine nucleotides and ferrous ion was indicated.

Alcohols↗
PubMed1974

Characterization of Escherichia coli flagellar mutants that are insensitive to catabolite repression.

In Escherichia coli, the synthesis of the flagellar organelle is sensitive to catabolite repression. Synthesis requires the presence of the cyclic adenosine monophosphate receptor protein (Crp) and 3',5'-cyclic adenosine monophosphate (cAMP); i.e., mutants that lack Crp or adenylcyclase (Cya) synthesize no flagella. We isolated and characterized a series of mutants (cfs) that restored flagella-forming ability in a Crp strain of E. coli. The mutations in these strains were transferred onto episomes and they were then introduced into a variety of other strains. The presence of the mutation resulted in flagella synthesis in Cya and Crp strains as well as in the wild type grown under conditions of catabolite repression. Deletion analysis and other genetic studies indicated that: (i) the cfs mutations had a dominant effect when they were in the transconfiguration in merodiploids: (ii) they occurred in or very close to the flaI gene: and (iii) their expression required the presence of an intact flaI gene adjacent to the cfs mutation. Biochemical studies showed that the synthesis of at least two flagellar polypeptides, the hook subunit and an amber fragment of flagellin, were absent in strains that carried a cya mutation. Their synthesis was depressed in strains grown under conditions of catabolite repression. The presence of the cfs mutation restored the specific synthesis of these two polypeptides. We suggest that the formation of the flaI gene product is the step in flagellar synthesis that is catabolite sensitive and requires cAMP. We propose a regulatory function for the product of the flaI gene.

Adenylyl Cyclases↗
PubMed1973

The uptake of 2-deoxy-D-glucose by Pseudomonas aeruginosa and its regulation.

The non-metabolizable glucose analogue 2-deoxy-d-glucose is taken up by Pseudomonas aeruginosa against a concentration gradient, in a predominantly unchanged form. d-Glucose competitively inhibits 2-deoxy-d-glucose uptake and also causes a rapid exit of intracellular 2-deoxy-d-glucose. Thus these two sugars share the same stereospecific carrier system, and glucose transport can be studied reliably with 2-deoxy-d-glucose. The transport system is inducible, and is strongly repressed by a number of organic acids such as acetate, citrate, succinate, fumarate and malate, even in the presence of adequate excess of the inducer (d-glucose). Repression by organic acids can be relieved by transferring cells to a glucose medium, but in the presence of chloramphenicol the cells fail to recover from repression, indicating that the formation of the transport system involves the synthesis of protein. The results demonstrate that the regulation of glucose metabolism effected by citric acid-cycle intermediates in P. aeruginosa is manifest at the level of the glucose-transport system.

Acetates↗