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At least 325 records · Page 18Linked to original sources
PubMed1973

S-adenosyl methionine-mediated repression of methionine biosynthetic enzymes in Saccharomyces cerevisiae.

S-adenosylmethionine (SAM) has been shown to provoke repression of some methionine-specific enzymes in wild-type cells, namely, adenosine triphosphate sulfurylase, sulfite reductase, and homocysteine synthetase. Repressive effects observed in SAM-supplemented cultures should be due to SAM per se, since the intracellular pool of SAM increases while the intracellular pool of methionine remains low and constant. Derepression brought about by methionine limitation is accompanied by a severe decrease in SAM as well as methionine pool sizes, although methionine adenosyl transferase is slightly derepressed. Different hypotheses have been considered to account for the previously reported implication of methionyl transfer ribonucleic acid and the presently reported SAM effects in this regulatory process.

Adenosine↗
PubMed1968

Catabolite repression in Escherichia coli. A study of two hypotheses.

1. Two hypotheses to account for general catabolite repression of the lactose enzymes in Escherichia coli were tested: the dilution model of Palmer & Moses (1967), and the specific catabolite repressor model of Loomis & Magasanik (1965, 1967). 2. The dilution model predicts that in mutants lacking the i-o regulation system the differential rate of beta-galactosidase synthesis should increase when amino acid-synthesizing enzymes are repressed by the presence of amino acids in the medium. It also predicts that with such mutants the total absence of P(i) from the medium should not result in the complete cessation of beta-galactosidase synthesis that is observed with wild-type cells. 3. Neither prediction was confirmed experimentally, and it is concluded that this model cannot explain catabolite repression. 4. The specific repressor hypothesis depends on the properties of a strain of E. coli carrying the CR(-) mutation. It requires both that cells of this genotype should be totally resistant to general catabolite repression and that this resistance should be specific for the lactose enzymes. 5. In fact the synthesis of beta-galactosidase by CR(-) cells, though showing resistance to catabolite repression by growth on glucose, was found to be repressed in several other circumstances. 6. Two other inducible enzymes, l-tryptophanase and d-serine deaminase, also showed resistance to repression by glucose in CR(-) cells. 7. It is concluded that this model, too, does not account for general catabolite repression. 8. Strains carrying deletions at either end of the lactose operon that extend into the structural genes of the operon continue to exhibit catabolite repression. 9. These experiments appear to eliminate the possibility that catabolite repression operates at the level of DNA transcription, and suggest that repression affects instead the translation of messenger RNA into protein.

Caseins↗
PubMed1991

Beijerinckia indica var. penicillanicum penicillin V acylase: enhanced enzyme production by catabolite repression-resistant mutant and effect of solvents on enzyme activity.

Beijerinckia indica var. penicillanicum mutant UREMS-5, producing 168% more penicillin V acylase, was obtained by successive treatment with UV, gamma-irradiation and ethylmethane sulfonate. Penicillin V acylase production by the mutant strain was resistant to catabolite repression by glucose. Incorporation of glucose, sodium glutamate and vegetable oils in the medium enhanced enzyme production. The maximum specific production of penicillin V acylase was 244 IU/g dry weight of cells. Effect of solvents on hydrolysis of penicillin V by soluble penicillin V acylase and whole cells was studied. Methylene chloride, chloroform and carbon tetrachloride significantly stimulated the rate of penicillin V hydrolysis by whole cells.

Carbon Tetrachloride↗
PubMed1984

Catabolite repression of inositol dehydrogenase and gluconate kinase syntheses in Bacillus subtilis.

The regulation of induction of inositol dehydrogenase (EC 1.1.1.18) and gluconate kinase (EC 2.7.1.12) was studied in Bacillus subtilis. Inositol dehydrogenase is induced by myo-inositol and gluconate kinase is induced by D-gluconate. Both inductions were strongly repressed by rapidly metabolizable carbohydrates such as D-glucose, D-mannose, D-fructose and glycerol (D-glucose had the strongest repressive effect) but they were weakly repressed by slowly metabolizable carbohydrates. Although each carbohydrate exerted a stronger effect on the induction of inositol dehydrogenase than that of gluconate kinase, it showed a similar tendency with respect to the degree of repression of each induction. This catabolite repression could not be diminished by addition of cyclic AMP to medium. In addition, non-metabolizable D-glucose analogues had no or weak repressive effects. On the assumption that rapidly metabolizable carbohydrates might be metabolized to repress both inductions, it was investigated whether several mutants blocked in the Embden-Meyerhof pathway could produce metabolite(s) (repressor) to repress them. A phosphoglycerate kinase (EC 2.7.2.3) deficient mutant could produce the repressor from D-glucose, D-mannose, D-fructose and glycerol but other mutants could not produce it from carbohydrates unable to be metabolized in each mutant. Thus, catabolite repression of both enzyme inductions seemed to be under similar regulation. The identification of the possible repressor of the induction of in of inositol dehydrogenase and gluconate kinase in vivo was discussed.

Bacillus subtilis↗
PubMed1967

Genetic and biochemical studies of nitrate reduction in Aspergillus nidulans.

1. In Aspergillus nidulans nitrate and nitrite induce nitrate reductase, nitrite reductase and hydroxylamine reductase, and ammonium represses the three enzymes. 2. Nitrate reductase can donate electrons to a wide variety of acceptors in addition to nitrate. These artificial acceptors include benzyl viologen, 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride, cytochrome c and potassium ferricyanide. Similarly nitrite reductase and hydroxylamine reductase (which are possibly a single enzyme in A. nidulans) can donate electrons to these same artificial acceptors in addition to the substrates nitrite and hydroxylamine. 3. Nitrate reductase can accept electrons from reduced benzyl viologen in place of the natural donor NADPH. The NADPH-nitrate-reductase activity is about twice that of reduced benzyl viologen-nitrate reductase under comparable conditions. 4. Mutants at six gene loci are known that cannot utilize nitrate and lack nitrate-reductase activity. Most mutants in these loci are constitutive for nitrite reductase, hydroxylamine reductase and all the nitrate-induced NADPH-diaphorase activities. It is argued that mutants that lack nitrate-reductase activity are constitutive for the enzymes of the nitrate-reduction pathway because the functional nitrate-reductase molecule is a component of the regulatory system of the pathway. 5. Mutants are known at two gene loci, niiA and niiB, that cannot utilize nitrite and lack nitrite-reductase and hydroxylamine-reductase activities. 6. Mutants at the niiA locus possess inducible nitrate reductase and lack nitrite-reductase and hydroxylamine-reductase activities. It is suggested that a single enzyme protein is responsible for the reduction of nitrite to ammonium in A. nidulans and that the niiA locus is the structural gene for this enzyme. 7. Mutants at the niiB locus lack nitrate-reductase, nitrite-reductase and hydroxylamine-reductase activities. It is argued that the niiB gene is a regulator gene whose product is necessary for the induction of the nitrate-utilization pathway. The niiB mutants either lack or produce an incorrect product and consequently cannot be induced. 8. Mutants at the niiribo locus cannot utilize nitrate or nitrite unless provided with a flavine supplement. When grown in the absence of a flavine supplement the activities of some of the nitrate-induced enzymes are subnormal. 9. The growth and enzyme characteristics of a total of 123 mutants involving nine different genes indicate that nitrate is reduced to ammonium. Only two possible structural genes for enzymes concerned with nitrate utilization are known. This suggests that only two enzymes, one for the reduction of nitrate to nitrite, the other for the reduction of nitrite to ammonium, are involved in this pathway.

Aspergillus↗
PubMed1971

Galactose-specific messenger ribonucleic acid contents in Escherichia coli.

A method is described for measuring the proportion of galactose-specific mRNA (gal-mRNA) in the total RNA extracted from pulse-labelled cells of Escherichia coli K12, by DNA-RNA hybridization with DNA prepared from bacteriophage lambdadg. RNA from wild-type E. coli was compared with RNA from a homogenote carrying the gal operon both in the chromosome and in a substituted sex-factor, and with RNA from a deletion strain that carried the galactose operon only in the exogenote. In each case the cultures were induced with fucose. Under these conditions the amount of gal-mRNA was found to be proportional to the content of galactokinase in the different cultures, and to the gene frequency. The amounts of gal-mRNA in an O(c) mutant and an R(-) mutant were also proportional to the observed contents of galactokinase. In cultures repressed for the enzymes of the galactose operon with thiomethylgalactoside, the content of gal-mRNA was higher than expected from the content of galactokinase. Possible explanations of this finding are discussed.

Chromosomes, Bacterial↗
PubMed1982

Repression of cytidine triphosphate synthetase in Salmonella typhimurium by pyrimidines during uridine nucleotide depletion.

Regulation of the synthesis of cytidine triphosphate (CTP) synthetase (EC 6.3.4.2) was investigated in Salmonella typhimurium. CTP synthetase appeared to be repressed only when intracellular concentrations of uridine nucleotides were significantly lowered. Under such nucleotide pool conditions, a cytidine compound and, to a lesser degree, a thymidine compound appeared as putative repressing metabolites of enzyme synthesis.

Carbon-Nitrogen Ligases↗
PubMed1993

Regulation of methylthioribose kinase by methionine in Klebsiella pneumoniae.

5-Methylthioribose (MTR) kinase catalyses a key step in the recycling of methionine from 5'-methylthioadenosine, a co-product of polyamine biosynthesis, in Klebsiella pneumoniae. In defined medium lacking methionine, K. pneumoniae exhibits abundant MTR kinase activity. When the bacterium is transferred to a medium containing 10 mM-methionine, the specific activity of MTR kinase decreases in a fashion consistent with repression of new enzyme synthesis and dilution of existing enzyme by cell division. The specific activity of methionine synthase decreases to a similar degree under the same conditions. In Escherichia coli and Salmonella typhimurium, the gene for methionine synthase is co-ordinately controlled as part of the methionine regulon. Taken together, our results indicate that a methionine regulon may function in K. pneumoniae and that expression of MTR kinase may be under its control.

Dose-Response Relationship, Drug↗
PubMed1994

The glucose-starvation stimulon of Escherichia coli: induced and repressed synthesis of enzymes of central metabolic pathways and role of acetyl phosphate in gene expression and starvation survival.

Proteins of the glucose-starvation stimulon were identified by using two-dimensional gel electrophoresis and the gene-protein database of Escherichia coli. Members of this stimulon included enzymes of the Embden-Meyerhof-Parnas (EMP) pathway, phosphotransacetylase (Pta) and acetate kinase (AckA) of the acetyl phosphate/acetate production pathway, and formate transacetylase. The synthesis of these enzymes was found to be induced concomitantly with the decreased synthesis of enzymes of the Krebs cycle. Thus, the modulation in the synthesis of specific proteins during aerobic glucose starvation is, in part, similar to the response of cells shifted to anaerobiosis. These modulations suggest that the glucose-starved cell increases the relative flow of carbon through the Pta-AckA pathway. Indeed, the ability to synthesize acetyl phosphate, an intermediate of the pathway, appears to be indispensable for glucose-starved cells as pta and pta-ackA double mutants were found to be impaired in their ability to survive glucose starvation. The survival characteristics of ackA mutants and the wild-type parent were indistinguishable. Moreover, the pta mutant failed to induce several proteins of the glucose-starvation stimulon.

Acetyltransferases↗
PubMed1972

Physiological studies on ergot: further studies on the induction of alkaloid synthesis by tryptophan and its inhibition by phosphate.

The failure of l-leucine to stimulate ergot alkaloid production in a synthetic medium indicates that the previously observed stimulation by tryptophan and tryptophan analogues does not merely represent a nutritional effect. Tryptophan, but not mevalonate or 5-methyltryptophan, is able to overcome the inhibition of alkaloid synthesis by high levels of inorganic phosphate. Therefore, high phosphate levels seem to limit the synthesis of tryptophan; they may, in addition, prevent induction of alkaloid synthesis by preventing accumulation of tryptophan. Experiments which indicate a 2- to 3-fold temporary increase of intracellular free tryptophan and a 20- to 25-fold increase of tryptophan synthetase activity during the transition period between growth and alkaloid production phase are in agreement with the previously postulated induction of alkaloid synthesis by tryptophan. The latter experiments also indicate 4- to 6-fold repression of this enzyme by tryptophan.

Amino Acids↗
PubMed1993

Effect of glpT and glpD mutations on expression of the phoA gene in Escherichia coli.

In vivo 31P nuclear magnetic resonance analysis of Escherichia coli cells showed that the intracellular concentration of P(i) remained constant in wild-type and in a glpT mutant strain whether the cells were grown on excess (2 mM) P(i) or sn-glycerol-3-phosphate as a phosphate source. The function of the phoA promoter (measured by beta-galactosidase activity in a phoA-lacZ fusion strain) was repressed when glpT+ cells were utilizing sn-glycerol-3-phosphate as the sole source of phosphate. These cells were devoid of alkaline phosphatase activity. However, the phoA promoter was fully active in a glpT mutant. These results indicated that the repression of the enzyme synthesis was not due to a variation in the level of cytoplasmic P(i) but was due to the P(i) excreted into the periplasm and/or to the medium.

Alkaline Phosphatase↗