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PubMed1973

Role of adenosine 3',5'-cyclic monophosphate and its specific binding protein in the regulation of D-serine deaminase synthesis.

Adenosine 3',5'-cyclic monophosphate (cyAMP) and the cyAMP-binding protein are necessary for efficient induction of d-serine deaminase (Dsdase) synthesis in dsdC(+)dsdO(+) and dsdC dsdO(+) strains of Escherichia coli K-12, and for constitutive synthesis in dsdC dsdO(+) strains. Neither is required in dsdO strains, confirming previous indications that in dsdO mutants Dsdase synthesis is not subject to catabolite repression control. Since efficient Dsdase synthesis in dsdC(+) and dsdC strains that are dsdO(+) requires the cyAMP-binding protein, which acts at the level of transcription in other systems, it is concluded that catabolite repression acts at the level of transcription of the Dsdase structural gene. Since catabolite repression is reversed by the inducer, d-serine in dsdC dsdO(+) strains, it is concluded that induction also acts at the level of transcription in this system. The dsdC strains were found to be much more sensitive to induction by d-serine than are dsdC(+) strains under conditions of catabolite repression, whether the repression was caused by glucose or by loss of ability to form cyAMP or cyAMP-binding protein. This suggests that a d-serine-dsdC complex may be able to replace partially the cyAMP:cyAMP-binding protein action in initiation of Dsdase messenger ribonucleic acid synthesis-a positive control effect.

Carrier Proteins↗
PubMed1982

Repression of endo-1,4-beta-glucanase formation in Penicillium janthinellum and product inhibition of its 1,4-beta-glucanases and cellobiases.

Endo-1,4-beta-glucanase formation of Penicillium janthinellum was repressed by glucose, sophorose, and glycerol. Chromatography on DEAE-Sephadex A-50 was employed to separate the 1,4-beta-glucanases from two cellobiases. The 1,4-beta-glucanases were inhibited competitively by cellobiose and glucose, and the two cellobiases were inhibited by glucose and glucono-delta-lactone.

Cellulase↗
PubMed1995

Glucokinase and cytosolic phosphoenolpyruvate carboxykinase (GTP) in the human liver. Regulation of gene expression in cultured hepatocytes.

Glucokinase and phosphoenolpyruvate carboxykinase are key enzymes of glucose metabolism in the rat liver. The former is considered to be instrumental in regulating glucose hepatic release/uptake according to the glycaemia level, and cytosolic phosphoenolpyruvate carboxykinase is a major flux-generating enzyme for gluconeogenesis. The level of expression of both enzymes and the regulation of their mRNAs in the human liver cell were investigated. Surgical biopsies of liver from patients undergoing partial hepatectomies and parenchymal hepatocytes derived from the biopsies were used to assay glucokinase, hexokinase and phosphoenolpyruvate carboxykinase activities. Hepatocytes were placed in culture and the actions of insulin, glucagon and cAMP on glucokinase and phosphoenolpyruvate carboxykinase mRNAs were studied. The main results are: (a) glucokinase accounts for 95% of the glucose phosphorylation activity of human hepatocytes, although this fact is masked in assays of total liver tissue; (b) glucokinase activity is set at a lower level in human hepatocytes than in rat hepatocytes, and vice-versa for the gluconeogenic enzyme phosphoenolpyruvate carboxykinase; and (c) as previously shown in rat liver, glucokinase and phosphoenolpyruvate carboxykinase mRNAs are regulated in a reciprocal fashion in human hepatocytes, insulin inducing the first enzyme and repressing the latter, whereas glucagon has opposite effects. These data have interesting implications with respect to metabolic regulation and intracellular hormone signaling in the human liver.

Adult↗
PubMed1992

Metabolic regulation of rice alpha-amylase and sucrose synthase genes in planta.

Isolated rice embryos were used to investigate the regulatory effects of endosperm extracts and pure sugars on the expression of alpha-amylase gene RAmy3D and a sucrose synthase gene homologous to the maize isozyme Ss2. The high-level expression of RAmy3D in the scutella of isolated embryos could be inhibited by a variety of sugars as well as endosperm extracts from germinated rice grains. Glucose, at a concentration of 250 mM, was most effective in repressing RAmy3D mRNA accumulation. Furthermore, this repression was reversible. Interestingly, RAmy3D repression was always accompanied by the induction of sucrose synthase gene expression. These results support a model in which the expression of alpha-amylase and sucrose synthase genes in the rice scutellum are counter-regulated by the influx of sugars from the endosperm.

Animals↗
PubMed1984

Autogenous repression of Escherichia coli threonyl-tRNA synthetase expression in vitro.

Escherichia coli threonyl-tRNA synthetase (EC 6.1.1.3) expression has been examined in an acellular protein-synthesizing system programmed with a plasmid DNA carrying thrS, infC, pheS, and pheT, the gene for threonyl-tRNA synthetase, initiation factor 3, and the two protomers of phenylalanyl-tRNA synthetase (EC 6.1.1.20), respectively. The initial rate of synthesis of L-[35S]methionine-labeled threonyl-tRNA synthetase is markedly reduced by the addition of homogeneous RNase-free threonyl-tRNA synthetase to the assay, not by that of phenylanyl- or tyrosyl-tRNA synthetase (EC 6.1.1.1). The inhibition is 50% in the presence of 0.25 microM threonyl-tRNA synthetase and reaches 90% with 2 microM enzyme. Synthesis of mRNA in the acellular DNA-dependent protein-synthesizing system has been measured by molecular hybridization to gene-specific lambda DNA probes corresponding to thrS, pheS, and pheT. The addition to the assay of 2 microM threonyl-tRNA synthetase does not affect the extent of mRNA hybridizing to the thrS-specific DNA probe. This result is interpreted as reflecting an effect of the synthetase on its expression at the translational level. Analysis of the DNA sequence of the thrS gene predicts several potential secondary structures capable of forming in the thrS mRNA. One of these potential structures is a cloverleaf. The possible role of such structures in controlling expression of thrS is discussed.

Amino Acyl-tRNA Synthetases↗
PubMed1975

Glucose repression of enterotoxins A, B and C and other extracellular proteins in staphlyococci in batch and continuous culture.

The production of enterotoxins, lipase and total extracellular protein by four strains of Staphylococcus aureus grown in batch culture at a controlled pH of 6.5 in a completely defined medium was markedly reduced by glucose or glycerol constantly maintained at 0.I M. A concomitant increase in the production of deoxyribonuclease, up to 13-fold, showed however that not all extracellular proteins are under the same control mechanism. The presence of glucose and glycerol in the medium also resulted in a rapid increase in the specific growth rate. However, growth of S. aureus s6 in Mgilimited continuous culture showed that glucose repression of enterotoxin B when the growth rate was held constant was more than twice that in batch culture. Therefore glucose repression can occur independently of an increase in growth rate. The specific rate of production of enterotoxin B, lipase, deoxyribonuclease, beta-haemolysin and total extracellular protein by S. aureus s6 increased as the growth rate increased from 0.07 to 0.24 h-1. Non-replicating cells grown in the absence of glucose produced considerable amounts of enterotoxin, and production was not repressed by the presence of glucose in the resuspension medium. In contrast, no enterotoxin B or C was obtained from nonreplicating cells grown in the presence of glucose. Chloramphenicol completely inhibited enterotoxin production by non-replicating cells, indicating that synthesis of new protein was required.

Bacterial Proteins↗
PubMed1974

Proline excretion and indirect suppression in Escherichia coli and Salmonella typhimurium.

The last step in proline biosynthesis in Escherichia coli K-12, Salmonella typhimurium LT7, and a number of other enterobacterial isolates is regulated so that no proline is excreted, even if excess Delta(1)-pyrroline-5-carboxylate, the immediate precursor of proline, is added to a culture. In proline auxotrophs blocked at an early step in proline biosynthesis (proA or proB), reversion to prototrophy is often due to a mutation in the arginine pathway which diverts N-acetyl glutamate gamma-semialdehyde to proline synthesis, thus bypassing the proA or proB block. In such double mutants (proAB, argD), the last step in proline synthesis appears to be unregulated, since proline is excreted. Feedback inhibition and repression of the arginine pathway overcomes indirect suppression (restoring the Pro(-) phenotype), but proline regulation is not restored; double mutants still excrete proline when fed Delta(1)-pyrroline-5-carboxylate exogeneously. A new class of proline analogue-resistant mutant, due to mutation at argD, is also described.

Arginine↗
PubMed1980

Metabolite gene regulation: imidazole and imidazole derivatives which circumvent cyclic adenosine 3',5'-monophosphate in induction of the Escherichia coli L-arabinose operon.

Imidazole, histidine, histamine, histidinol phosphate, urocanic acid, or imidazolepropionic acid were shown to induce the L-arabinose operon in the absence of cyclic adenosine 3',5'-monophosphate. Induction was quantitated by measuring the increased differential rate of synthesis of L-arabinose isomerase in Escherichia coli strains which carried a deletion of the adenyl cyclase gene. The crp gene product (cyclic adenosine 3',5'-monophosphate receptor protein) and the araC gene product (P2) were essential for induction of the L-arabinose operon by imidazole and its derivatives. These compounds were unable to circumvent the cyclic adenosine 3',5'-monophosphate in the induction of the lactose or the maltose operons. The L-arabinose regulon was catabolite repressed upon the addition of glucose to a strain carrying an adenyl cyclase deletion growing in the presence of L-arabinose with imidazole. These results demonstrated that several imidazole derivatives may be involved in metabolite gene regulation (23).

Aldose-Ketose Isomerases↗
PubMed1985

Rat liver carbonic anhydrase I is not sexually dimorphic but is estrogen repressible.

Carbonic anhydrase (CA) isozymes CAII and CAIII are known to exhibit sexual dimorphism in rat liver, and the levels of these isozymes are affected by sex hormones. In this paper we show that the isozyme CAI is present at low levels in rat liver, with no difference in concentration between male and female rats. Estrogen and diethylstilbestrol reduce CAI levels in both sexes.

Animals↗
PubMed1966

Coordinate synthesis of heme and apoenzyme in the formation of tryptophan pyrrolase.

Reciprocal control mechanisms between hemoprotein and 8-aminolevulinic acid synthetase take part in coordinate synthesis of the heme and apoenzyme moieties of tryptophan pyrrolase. Stimulation of heme biosynthesis increases tryptophan pyrrolase, whereas enhancement of heme binding by apotryptophan pyrrolase secondarily increases the formation of delta-aminolevulinic acid synthetase, the rate-limiting enzyme in heme formation. Tryptophan-mediated induction of delta-aminolevulinic acid synthetase suggests that heme participates in repression of that enzyme

Amino Acids↗
PubMed1966

The de-repression of thiamine biosynthesis by adenosine a tool for investigating this biosynthetic pathway.

1. Growth of Salmonella typhimurium LT2 in the presence of adenosine was shown to cause enormous synthesis of thiamine in washed-cell suspensions. 2. Evidence that this was due to de-repression and not an accumulation of precursors was obtained by using a mutant blocked in the biosynthesis of the thiazole moiety, which showed a similarly large synthesis of the pyrimidine of thiamine. 3. The specific requirements for a source of energy, nitrogen and sulphur were investigated, and indicated new synthesis in this system.

Biological Assay↗
PubMed1994

Specific association of human telomerase activity with immortal cells and cancer.

Synthesis of DNA at chromosome ends by telomerase may be necessary for indefinite proliferation of human cells. A highly sensitive assay for measuring telomerase activity was developed. In cultured cells representing 18 different human tissues, 98 of 100 immortal and none of 22 mortal populations were positive for telomerase. Similarly, 90 of 101 biopsies representing 12 human tumor types and none of 50 normal somatic tissues were positive. Normal ovaries and testes were positive, but benign tumors such as fibroids were negative. Thus, telomerase appears to be stringently repressed in normal human somatic tissues but reactivated in cancer, where immortal cells are likely required to maintain tumor growth.

Base Sequence↗
PubMed1976

The effect of nitrogen limitation on catabolite repression of amidase, histidase and urocanase in Pseudomonas aeruginosa.

In Pseudomonas aeruginosa, the synthesis of histidase, urocanase and amidase is severly repressed when succinate is added to a culture growing in pyruvate + ammonium salts medium. When growth is nitrogen-limited, catabolite repression by succinate of histidase and urocanase synthesis does not occur but succinate repression of amidase synthesis persists. Amidase synthesis is not regulated in the same way as histidase synthesis by the availability of other nitrogen compounds for growth. Growth of P. aeruginosa strain PACI in succinate + histidine media is nitrogen-limited since this strain is defective in a histidine transport system. When methyl-ammonium chloride is added to succinate + histidine media, growth inhibition occurs. Mutants isolated from succinate + histidine + methylammonium chloride plates were found to be resistant to catabolite repression by succinate even in ammonium salts media. It is suggested that the hut genes of P. aeruginosa may be regulated in the same way as in Klebsiella aerogenes, by induction by urocanate and activation by either the cyclic AMP-dependent activator protein or by glutamine synthetase.

Amidohydrolases↗
PubMed1974

Mutations in the L-arabinose operon of Escherichia coli B-r that result in hypersensitivity to catabolite repression.

Two independent mutants resistant to l-arabinose inhibition only in the presence of d-glucose were isolated from an l-arabinose-sensitive strain containing the araD139 mutation. Preliminary mapping studies indicate that these mutations are closely linked to the araIOC region. Addition of d-glucose to growing cultures of these mutants results in a 95 to 98% repression of ara operon expression, as compared to a 50% repression of the parental control. Since cultures of both mutant and parental strains undergo a 50% repression of lac operon expression upon addition of glucose, the hypersensitivity to catabolite repression exhibited by these mutants is specific for the ara operon. Addition of cyclic adenosine monophosphate reverses the catabolite repression of the ara operon in both mutant and parent strains to 70 to 80% of the control. It is suggested that in these mutants the affinity of the ara operon initiator region for the cAMP-catabolite-activator protein complex may have been altered.

Arabinose↗
PubMed1990

Mutual transrepression of Fos and the glucocorticoid receptor: involvement of a functional domain in Fos which is absent in FosB.

In this study, we show that Fos protein can repress transactivation by the glucocorticoid receptor (GR). In addition, we demonstrate that GR is capable of inhibiting, in a hormone-dependent fashion, Fos-mediated transactivation of AP-1 dependent transcription. Moreover, repression of the serum response element by Fos is abolished by the GR in the presence of hormone. Transrepression of glucocorticoid mediated induction involves a region of Fos, located between amino acids 40 and 111, to which no function has been previously assigned, and which is poorly conserved among Fos, FosB and Fra-1. In agreement with this finding, FosB is not capable of transrepressing GR activation of transcription, representing the first functional difference between Fos and FosB. We have mapped the domain of the GR which is required for repression of AP-1 dependent transcription, to the region of central DNA binding domain. Our results suggest that Fos and the GR may form transcriptionally inactive complexes and point to a regulatory interrelationship between different signal transduction pathways.

Amino Acid Sequence↗
PubMed1975

Subcellular distribution of yeast invertase isoenzymes.

Homogenates from yeast cells contain 1% or less of sedimentable invertase activity. Sedimentability is equally low in homogenates from cells repressed or derepressed with regard to invertase secretion. Intracellulary, the mannanprotein form of invertase is largely localized in vacuoles whereas the small isoenzyme is largely present in the soluble cell fraction. These findings indicate that vesicles are not involved in the secretion of invertase. A soluble mode of invertase secretion is discussed.

Cytoplasmic Granules↗
PubMed1972

Regulation of synthesis of methionyl-, prolyl-, and threonyl-transfer ribonucleic acid synthetases of Escherichia coli.

Proline- and threonine-restricted growth caused a three- to fourfold derepression of the differential rate of synthesis of the prolyl- and threonyl-transfer ribonucleic acid (tRNA) synthetases, respectively. Similarly, there was approximately a 24-fold derepression in the rate of synthesis of methionyl-tRNA synthetase during methionine restriction. Addition of the respective amino acids to such derepressed cultures resulted in a repression of synthesis of their cognate synthetases. These results support previous findings and further strengthen the idea that the formation of aminoacyl-tRNA synthetases is regulated by some mechanism which is mediated by the cognate amino acids.

Aerobiosis↗
PubMed1975

Reversible inactivation of the isocitrate dehydrogenase of Escherichia coli ML308 during growth on acetate.

During aerobic growth of Escherichia coli ML308 on acetate as sole carbon source, the apparent synthesis of isocitrate dehydrogenase was repressed relative to cultures on other carbon sources, such as glucose, which do not employ the glyoxylate bypass as an anaplerotic sequence. When cells were removed from an acetate medium, or when compounds were added which made the operation of the glyoxylate bypass unnecessary, the activity of isocitrate dehydrogenase rapidly increased 3- to 4-fold but fell again on restoration to an acetate medium. Changes in activity were rapid and, furthermore, could be demonstrated in the absence of protein synthesis. It is thus improbable that the mechanism involved degradation or de novo synthesis of the enzyme protein. Oxaloacetate and glyoxylate showed concerted inhibition of isocitrate dehydrogenase which could be relieved by dialysis. Because extracts of low enzyme activity, derived from acetate-metabolizing cells, could not be stimulated by dialysis or by addition of a wide range of metabolites, it is unlikely that low molecular weight, freely dissociable effectors were responsible for stimulation or inhibition of activity. Control of isocitrate dehydrogenase permitted the efficient utilization of acetate as sole source of carbon and energy but perserved the capacity of the cell to respond rapidly to an improvement in nutritional conditions. A limited survey showed that the mechanism is common but not universal among strains of E. coli and occurs in at least one strain each of Klebsiella aerogenes, Salmonella typhimurium and Serratia marcescens.

Acetates↗