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PubMed1980

Repression and derepression of the enzymes of the pyrimidine biosynthetic pathway in Salmonella typhimurium.

Activities of five enzymes of the pyrimidine biosynthetic pathway and one enzyme involved in arginine synthesis were measured during batch culture of Salmonella typhimurium. Aspartate carbamoyltransferase, dihydroorotase, and the arginine pathway enzyme, ornithine carbamoyltransferase, remained constant during the growth cycle but showed a sharp decrease in activity after entering the stationary phase. Dihydroorotate dehydrogenase, orotate phosphoribosyltransferase and orotidine-5'-monophosphate (OMP) decarboxylase showed peaks of activity corresponding to the mid-point of the exponential phase of growth while remaining comparatively stable in the stationary phase. Derepression studies carried out by starving individual pyrimidine (Pyr-) deletion mutants for uracil showed that the extent of derepression obtained for aspartate carbamoyltransferase, dihydroorotase and dihydroorotate dehydrogenase depended on the location of the pyr gene mutation. Orotate phosphoribosyltransferase and OMP decarboxylase derepression levels were independent of the location of the pyr mutation. Aspartate carbamoyltransferase showed the greatest degree of derepression of the six enzymes studied, with pyrA strains (blocked in the first step of the pathway) showing about twice as much derepression as pyrF strains (blocked in the sixth step of the pathway). A study of the kinetics of repression on derepressed levels of the pyrimidine enzymes produced data that were compatible with dilution of specific activity by cell division when repressive amounts of uracil were added to the derepression medium.

Aspartate Carbamoyltransferase↗
PubMed1997

Activation and repression of the activity of a lead ribozyme by the combination of Pb2+ and Mg2+.

The effect of Pb2+ and Mg2+ on the activity of a lead ribozyme with modified sequences has been studied. At low Pb2+ concentrations, cleavage at a previously reported site (site a) is observed. At higher Pb2+ concentrations, cleavage at a new site (site b) adjacent to site a is observed, while the cleavage at site a is repressed. On the addition of a certain amount of Mg2+, the cleavage at site a is enhanced by almost fourfold, while the cleavage at site b is repressed. Further addition of Mg2+ represses the cleavage at both sites. CD analysis indicates that the structure and stability of the lead ribozyme change depending on the metal conditions. Activation and repression of the activity by the combination of Pb2+ and Mg2+ are rationalized by considering that the two metals compete with each other for binding at two metal-binding sites.

Base Sequence↗
PubMed1975

Cellulase location in Cellvibrio fulvus.

The location of cellulase in C. fulvus depends on the carbon source for growth and the age of the culture. When cells were grown on glucose or cellobiose all CMC-hydrolyzing enzyme was cell-bound but only part of the activity was located on the cell surface. Treatment of cells with EDTA, lysozyme, and detergents and subsequent fractionation experiments showed that cellulase was also located in the periplasm and bound to a membrane fraction. Growth on cellulose gave cell-free cellulase active against CMC. The enzyme was repressed by glucose but formed at a constant differential rate on cellobiose and amylose. This rate was 8-10 times lower than on cellulose and possible reasons for this are discussed.

Amylose↗
PubMedDate not supplied

[Metabolism of a psychrophilic bacterium from fresh water].

Psychophilic microorganisms, able to grow at 0-1 degrees C, were isolated from water obtained from the Paraná River at Rosario. One of the strains, R-12, was identified as Pseudomonas fluorescens according to the description in Bergey's Manual of Determinative Bacteriology (8th Ed., 1974). The microorganism was able to grow in liquid minimal medium with glucose, acetate, glutamate or casein hydrolysate as sole carbon source, at 20 degrees C. The enzymes of the Entner-Doudoroff pathway were induced in cells grown on glucose. The Krebs cycle was apparently operative in all cases; the lower levels of citrate synthase and isocitrate dehydrogenase were found in glucose-grown cells. Isocitrate lyase was present at a high concentration, and malate synthase considerably increased, in acetate-grown cells, thus suggesting the operation of the glyoxylate cycle. When cells were grown on glucose the anaplerotic function was probably fulfilled by pyruvate carboxylase, although phosphoenolpyruvate carboxylase was also present. The gluconeogenic enzyme phosphoenolpyruvate carboxykinase was repressed by glucose; malic enzyme was repressed by acetate. The regulatory patterns shown by citrate synthase and pyruvate carboxylase were similar to those described for the enzymes from other Pseudomonas. Whole cells of the R-12 strain were able to decarboxylate the aminoacids serine, aspartate and glutamate. Aspartate aminotransferase was present at high levels in aminoacid-grown cells, thus suggesting a catabolic role, whereas glutamate dehydrogenase had increased levels in glucose - or acetate-grown cells, suggesting that it fulfilled a mainly biosynthetic role.

Citric Acid Cycle↗
PubMed1989

Isolation and characterization of a laccase-derepressed mutant of Neurospora crassa.

Laccase from the ascomycete Neurospora crassa is an inducible secretory enzyme. Production of this enzyme is repressed in vegetative cultures but can be induced by treatment with low concentrations of cycloheximide. Isolation and characterization of a derepressed mutant, the lah-1 mutant, that is capable of producing laccase in vegetative cultures without induction by cycloheximide are described. The lah-1 mutation is mapped between nit-2 and leu-3 on linkage group I, and it behaved as a recessive mutation in a forced heterokaryon. No differences were detected biochemically or immunologically between the laccase protein produced by the lah-1 mutant in the absence of cycloheximide and that induced with cycloheximide in the wild-type strain. This suggests that both laccases (66 kilodaltons) are products of the same structural gene. Relative amounts of laccase in the culture filtrate of the lah-1 mutant were much higher than those induced with cycloheximide in the wild-type strain, demonstrating high efficiency of the lah-1 mutant in production and secretion of laccase. The time course of laccase production by the lah-1 mutant revealed that expression of 66-kilodalton laccase was repressed in conidia and derepressed during vegetative mycelial growth. This suggests that a multiple regulatory mechanism is involved in the production and/or maturation of Neurospora laccase. The lah-1 mutant may be useful for identifying genes that regulate expression of the laccase gene in N. crassa.

Chromatography↗
PubMed1971

Biosynthesis of biotin: synthesis of 7,8-diaminopelargonic acid in cell-free extracts of Escherichia coli.

Cell-free extracts prepared from a biotin auxotroph of Escherichia coli were active in catalyzing the synthesis of 7,8-diaminopelargonic acid, an intermediate of the biotin pathway, from 7-oxo-8-aminopelargonic acid. The product was identified on the basis of its chromatographic characteristics and its biotin activities for biotin auxotrophs of E. coli. Enzyme activity was determined in a reaction coupled with the desthiobiotin synthetase system, which is required for the conversion of 7,8-diaminopelargonic acid to desthiobiotin, and by measuring the amount of desthiobiotin formed by microbiological assay. The reaction was stimulated by l-methionine and pyridoxal-5'-phosphate. l-Methionine could not be replaced by any other amino acids tested. Pyridoxamine and pyridoxamine-5'-phosphate were as active as pyridoxal phosphate. The enzyme, presumably an aminotransferase, was demonstrable in the parent strain of E. coli and all mutant strains tested with the exception of a strain which is able to grow on diaminopelargonic acid but not on 7-oxo-8-aminopelargonic acid. Furthermore, the enzyme was repressible by biotin. The results were consistent with the hypothesis that the biosynthesis of 7,8-diaminopelargonic acid from 7-oxo-8-aminopelargonic acid is an obligatory step in the biosynthetic pathway of biotin in E. coli.

Amines↗
PubMed1985

Neurospora glucamylase and a mutant affected in its regulation.

Neurospora glucamylase is a glucose-repressible extracellular enzyme. The enzyme was purified to homogeneity and found to have a molecular weight of 82,000 and to release glucose from either maltose or amylose. The rate of glucamylase synthesis increases more than 100-fold when cells are transferred from a glucose-containing medium to a glucose-free medium. Increased from a glucose-containing medium to a glucose-free medium. Increased production of glucamylase begins within 30 min of the transfer. Glucamylase is rapidly secreted into the medium. A mutant affecting the ability of glucose to repress the synthesis of the glucose-repressible extracellular enzymes glucamylase and invertase has been isolated and studied. The mutant constitutively synthesizes and secretes a glucamylase which is indistinguishable from the wild-type enzyme.

Electrophoresis, Polyacrylamide Gel↗
PubMed1980

Genetic and biochemical evidence for hexokinase PII as a key enzyme involved in carbon catabolite repression in yeast.

Mutants with reduced hexokinase activity previously isolated as resistant to carbon catabolite repression of invertase and maltase (Zimmermann and Scheel, 1977) were allele tested with mutant strains of Lobo and Maitra (1977) which had defects in one or several of the genes coding for glucokinase and the two unspecific hexokinases. It could be demonstrated, that the mutation abolishing carbon catabolite repression had occurred in a gene allelic to the structural gene of hexokinase PII. Moreover, the defective mutant allele for hexokinase PII isolated by Lobo and Maitra (1977) was also defective in carbon catabolite repression. Neither glucokinase nor hexokinase PI showed any effect on this regulatory system. Biochemical analysis in crude extracts also showed altered kinetic properties of hexokinases in the hex1 mutants. The results directly support the hypothesis previously put forward, that one of the hexokinases is not only active as a catalytic, but also as a regulatory protein.

Crosses, Genetic↗
PubMed1974

Effect of cyclic guanosine 3,5-monophosphate on the synthesis of enzymes sensitive to caatabolite repression in intact cells of Escherichia coli.

Cyclic guanosine 3',5'-monophosphate inhibits the synthesis of beta-galactosidase and tryptophanase in cultures of Escherichia coli growing in minimal media with glucose or glycerol as the carbon source. Cyclic guanosine 3',5'-monophosphate acts at the transcriptional level in the lac operon, it exerts its action at the promoter site of the operon, and requires the presence of functional cyclic adenosine 3',5'-monophosphate receptor protein.

Carbon Radioisotopes↗
PubMed1984

Genes affecting the regulation of SUC2 gene expression by glucose repression in Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae with defects in sucrose or raffinose fermentation were isolated. In addition to mutations in the SUC2 structural gene for invertase, we recovered 18 recessive mutations that affected the regulation of invertase synthesis by glucose repression. These mutations included five new snf1 (sucrose nonfermenting) alleles and also defined five new complementation groups, designated snf2, snf3, snf4, snf5, and snf6. The snf2, snf4, and snf5 mutants produced little or no secreted invertase under derepressing conditions and were pleiotropically defective in galactose and glycerol utilization, which are both regulated by glucose repression. The snf6 mutant produced low levels of secreted invertase under derepressing conditions, and no pleiotropy was detected. The snf3 mutants derepressed secreted invertase to 10-35% the wild-type level but grew less well on sucrose than expected from their invertase activity; in addition, snf3 mutants synthesized some invertase under glucose-repressing conditions.--We examined the interactions between the different snf mutations and ssn6, a mutation causing constitutive (glucose-insensitive) high-level invertase synthesis that was previously isolated as a suppressor of snf1. The ssn6 mutation completely suppressed the defects in derepression of invertase conferred by snf1, snf3, snf4 and snf6, and each double mutant showed the constitutivity for invertase typical of ssn6 single mutants. In contrast, snf2 ssn6 and snf5 ssn6 strains produced only moderate levels of invertase under derepressing conditions and very low levels under repressing conditions. These findings suggest roles for the SNF1 through SNF6 and SSN6 genes in the regulation of SUC2 gene expression by glucose repression.

Enzyme Repression↗
PubMed1999

Insulin-induced early growth response gene (Egr-1) mediates a short term repression of rat malic enzyme gene transcription.

In this report we have studied insulin regulation of malic enzyme (ME) gene transcription in rat H-35 hepatoma cells and localized the insulin-responsive region of the ME promoter between positions -177 and -102. This region contains a putative insulin response element (IRE-II). When nuclear extracts from untreated or insulin-treated H-35 cells were incubated with IRE-II, transcription factors Sp1 and Sp3 were observed to bind constitutively to this element, whereas insulin induces the quick and transient binding of an insulin response factor. This induction requires de novo protein synthesis. Competition and supershift assays demonstrated that the insulin response factor is the immediate-early gene Egr-1. In vitro assays revealed that Egr-1 displaces Sp1 from its binding site in IRE-II. Insulin induces Egr-1 mRNA, with a time course pattern that corresponds perfectly to the Egr-1 binding to IRE-II. This induction depends on the activation of mitogen-activated protein (MAP) kinase, and it is phosphatidylinositol 3-kinase-independent, as demonstrated with specific inhibitors for both pathways. By cotransfecting the wild-type or a dominant negative Ras, an upstream regulator of MAP kinase, we show that Ras inhibits ME promoter activity. Furthermore, overexpression of Egr-1 in H-35 cells represses the ME gene promoter in a dose-dependent manner. These results suggest that insulin induces a quick, transient, and Ras/MAP kinase-dependent activation of Egr-1 which leads to a transient repression of ME gene transcription. On a late phase, insulin would activate a different, Egr-1-independent pathway, which would result in activation of the ME gene.

Animals↗
PubMed1978

Involvement of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system in regulation of transcription of catabolic genes.

Synthesis of catabolite-sensitive enzymes is repressed in mutants defective in the general proteins (enzyme I and HPr) of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system (ptsI and ptsH mutations). To elucidate the mechanism of this phenomenon we constructed isogenic strains carrying pts mutations as well as different lesions of regulation of the lac operon or mutations affecting adenylate cyclase activity (cya mutation) and synthesis of cyclic AMP-receptor protein (crp mutation) Measurements of the differential rate of beta-galactosidase synthesis in these strains showed that the repressive effect of pts mutations was revealed in lac+, lacI, lacOc and cya bacteria, but it was lost in lacP and crp strains. It was concluded that mutational damage to the general components of the phosphoenolpyruvate-dependent phosphotransferase system diminishes activity of the lac promoter. The results obtained led to the conclusion that pts gene products (apparently phospho approximately HPr) are necessary for the initiation of transcription of catabolite-sensitive operons in E. coli.

DNA-Directed RNA Polymerases↗
PubMed1985

Differential sensitivities to glucose and galactose repression of gluconeogenic and respiratory enzymes from Saccharomyces cerevisiae.

The synthesis of isocitrate lyase was induced by the presence of ethanol in the chemostat reaching a specific activity of 200 mU X mg-1 at this induced state. In glucose-limited, derepressed cells, 20 mU X mg-1 were detected and under repressed conditions isocitrate lyase activity was not detected. The sensitivity of gluconeogenic enzymes: cytoplasmic malate dehydrogenase; fructose 1,6-bisphosphatase and isocitrate lyase as well as the mitochondrial enzymes NADH dehydrogenase and succinate cytochrome c oxidase to glucose and galactose repression were studied in chemostat cultures. Our results show that galactose was less effective as a repressor than glucose. Malate dehydrogenase was completely inactivated by glucose, whereas galactose only produced a 78% decrease of specific activity. Fructose 1,6-bisphosphatase and isocitrate lyase were completely inactivated by both sugars but at different rate. Glucose produced an 85% decrease of specific activity of the mitochondrial enzymes whereas galactose only decrease an 67%.

Culture Media↗
PubMed1992

The pho-2A mutant of Neurospora crassa which is deficient in Pi-repressible alkaline phosphatase (EC 3.1.3.1) is also defective in Pi-repressible acid phosphatase (EC 3.1.3.2).

1. The mycelial Pi-repressible acid phosphatase presented p-nitrophenylphosphatase activity with negative cooperativity and Michaelian behavior when synthesized by the wild-type and pho-2A mutant strains of Neurospora crassa, respectively. 2. The major acid phosphatase present in cell extracts of the pho-2A mutant of N. crassa grown in low Pi medium is more thermolabile (t1/2 = 4 min at 54 degrees C, pH 5.4) than that of the wild strain (stable for at least 80 min at 54 degrees C, pH 5.4). 3. The pho-2A mutant of N. crassa secreted a more thermolabile acid phosphatase (t1/2 = 30 min at 50 degrees C, pH 5.4) than the wild strain (t1/2 of at least 80 min at 50 degrees C, pH 5.4). 4. The pho-2A mutant of N. crassa synthesized a more thermolabile acid phosphatase (t1/2 = 37 min at 54 degrees C, pH 5.4) than the wild strain in high Pi medium (t1/2 = 14 min at 54 degrees C, pH 5.4). 5. The pleiotropic nature of the pho-2 locus and its possible involvement in the mechanism of phosphatase secretion by N. crassa are proposed.

4-Nitrophenylphosphatase↗
PubMed1975

Separate regulation of transport and biosynthesis of leucine, isoleucine, and valine in bacteria.

Since both transport activity and the leucine biosynthetic enzymes are repressed by growth on leucine, the regulation of leucine, isoleucine, and valine biosynthetic enzymes was examined in Escherichia coli K-12 strain EO312, a constitutively derepressed branched-chain amino acid transport mutant, to determine if the transport derepression affected the biosynthetic enzymes. Neither the iluB gene product, acetohydroxy acid synthetase (acetolactate synthetase, EC 4.1.3.18), NOR THE LEUB gene product, 3-isopropylmalate dehydrogenase (2-hydroxy-4-methyl-3-carboxyvalerate-nicotinamide adenine dinucleotide oxido-reductase, EC 1.1.1.85), were significantly affected in their level of derepression or repression compared to the parental strain. A number of strains with alterations in the regulation of the branched-chain amino acid biosynthetic enzymes were examined for the regulation of the shock-sensitive transport system for these amino acids (LIV-I). When transport activity was examined in strains with mutations leading to derepression of the iluB, iluADE, and leuABCD gene clusters, the regulation of the LIV-I transport system was found to be normal. The regulation of transport in an E. coli strain B/r with a deletion of the entire leucine biosynthetic operon was normal, indicating none of the gene products of this operon are required for regulation of transport. Salmonella typhimurium LT2 strain leu-500, a single-site mutation affecting both promotor-like and operator-like function of the leuABCD gene cluster, also had normal regulation of the LIV-I transport system. All of the strains contained leucine-specific transport activity, which was also repressed by growth in media containing leucine, isoleucine and valine. The concentrated shock fluids from these strains grown in minimal medium or with excess leucine, isoleucine, and valine were examined for proteins with leucine-binding activity, and the levels of these proteins were found to be regulated normally. It appears that the branched-chain amino acid transport systems and biosynthetic enzymes in E. coli strains K-12 and B/r and in S. typhimurium strain LT2 are not regulated together by a cis-dominate type of mechanism, although both systems may have components in common.

Acetolactate Synthase↗
PubMed1997

Ethanol represses thymidylate synthase and thymidine kinase at mRNA level in regenerating rat liver after partial hepatectomy.

The effects of ethanol on liver regeneration after partial hepatectomy were investigated. The injection of ethanol inhibited the increases in the activities of thymidylate synthase and thymidine kinase in regenerating rat liver at 24 h after partial hepatectomy in a dose-dependent manner, with a concomitant reduction in DNA content. Northern blot analysis showed that the inhibition of thymidylate synthase and thymidine kinase activities was caused by comparable decreases in their mRNA levels. The immunoblotting assay confirmed the protein levels of thymidylate synthase and thymidine kinase as proportional to the activity and mRNA levels. These findings suggest that ethanol inhibits DNA synthesis by the repression of mRNA levels of dTMP-synthesizing enzymes during liver regeneration.

Animals↗
PubMed1983

Nutritional regulation of degradation of aspartate transcarbamylase and of bulk protein in exponentially growing Bacillus subtilis cells.

The rate of degradation of aspartate transcarbamylase in exponentially growing Bacillus subtilis cells was determined by measurement of enzyme activity after the addition of uridine to repress further enzyme synthesis and by specific immunoprecipitation of the enzyme from cells grown in the presence of [3H]leucine. Aspartate transcarbamylase was degraded with a half-life of about 1.5 h in cells growing on a glucose-salts medium with NH4+ ions as the sole source of nitrogen. Replacement of NH4+ in this medium with a combination of the amino acids aspartate, glutamate, isoleucine, proline, and threonine reduced the degradation rate to an undetectable level. Various other amino acids and amino acid mixtures had smaller effects on the rate of degradation. The carbon source also influenced the degradation rate, but to a smaller extent than the nitrogen source. The effects of these nutritional variables on the rate of bulk protein turnover in growing cells were generally similar to their effects on degradation of aspartate transcarbamylase. Since the degradation of aspartate transcarbamylase has been shown to be 10 to 20 times faster than bulk protein turnover, the results suggest that a substantial portion of protein turnover in growing cells represents regulable, rapid degradation of a number of normal proteins, of which aspartate transcarbamylase is an example.

Amino Acids↗