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At least 811 records · Page 45Linked to original sources
PubMed1980

Regulation of lysine- and lysine-plus-threonine-inhibitable aspartokinases in Bacillus brevis.

Further studies on the expression of the two aspartokinase activities in Bacillus bovis are presented. Aspartokinase I (previously shown to be inhibited and repressed by lysine) was found to be repressed by diaminopimelate in the wild-type strain. However, in a mutant unable to convert diaminopimelate to lysine, starvation for lysine resulted in an increase in aspartokinase I activity. Thus, lysine itself or an immediate metabolite was the true effector of repression. Aspartokinase II (previously shown to be inhibited by lysine plus threonine) was repressed by threonine. Studies with the parent strain and auxotrophs inidicated that only threonine or an immediate metabolite of threonine was involved in this repression. Methionine and isoleucine were not effectors of any of the detected aspartokinase activities. Apart from inhibition and repression controls, a third as yet undefined regulatory mechanism operated to decrease the levels of both aspartokinases as growth declined, even in mutants in which repression control was absent. In thiosine-resistant, lysine-excreting mutants with elevated levels of aspartokinase, the increase in activity could always be attributed to one enzyme or the other, never both. The existence of separate structural genes for each aspartokinase is therefore suggested.

Aspartate Kinase↗
PubMed1989

cis sequences involved in modulating expression of Bacillus licheniformis amyL in Bacillus subtilis: effect of sporulation mutations and catabolite repression resistance mutations on expression.

Nutrient conditions which trigger sporulation also activate expression of the Bacillus licheniformis alpha-amylase gene, amyL. Glucose represses both spore formation and expression of amyL. A fusion was constructed between the B. licheniformis alpha-amylase regulatory and 5' upstream sequences (amyRi) and the Escherichia coli lacZ structural gene to identify sequences involved in mediating temporal activation and catabolite repression of the amyL gene in Bacillus subtilis. amyRi-directed expression in a variety of genetic backgrounds and under different growth conditions was investigated. A 108-base-pair sequence containing an inverted repeat sequence, ribosome-binding site, and 26 codons of the structural gene was sufficient to mediate catabolite repression of amyL. spo0 mutations (spo0A, spo0B, spo0E, and spo0H) had no significant effect on temporal activation of the gene fusion when the recipient strains were grown in nonrepressing medium. However, in glucose-grown cultures the presence of a spo0A mutation resulted in more severe repression of amyRi-lacZ. In contrast, a spo0H mutation reduced the repressive effect of glucose on amyRi-lacZ expression. The spo0A effect was relieved by an abrB mutation. Initiation of sporulation is not a prerequisite for either temporal activation or derepression of alpha-amylase synthesis. Mutations causing resistance to catabolite repression in B. subtilis GLU-47, SF33, WLN30, and WLN104 also relieved catabolite repression of amyRi-lacZ.

Bacillus↗
PubMed1996

Significance of HPr in catabolite repression of alpha-amylase.

CcpA and HPr are presently the only two proteins implicated in Bacillus subtilis global carbon source catabolite repression, and the ptsH1 mutation in the gene for the HPr protein was reported to relieve catabolite repression of several genes. However, alpha-amylase synthesis by B. subtilis SA003 containing the ptsH1 mutation was repressed by glucose. Our results suggest HPr(Ser-P) may be involved in but is not required for catabolite repression of alpha-amylase, indicating that HPr(Ser-P) is not the sole signaling molecule for CcpA-mediated catabolite repression in B. subtilis.

Bacillus subtilis↗
PubMed1976

Gene expression of the histidine operon.

Histidine biosynthesis in Salmonella typhi-murium and Escherichia coli is regulated through repression and feedback inhibition. Repression is triggered by the intracellular level of histidyl-tRNA whereas feedback inhibition is brought about by histidine itself, an allosteric inhibitor of the first biosynthetic enzyme. Several lines of evidence indicate that these two processes are interconnected and the first biosynthetic enzyme is itself a regulatory molecule for the his operon. The regulation seems to be exerted in a negative fashion, although a positive control cannot be excluded.

ATP Phosphoribosyltransferase↗
PubMed1977

[Gratuitous induction of beta-glucuronidase of Escherichia coli K 12 and the double repression mechanism].

Using natural inducers of beta-glucuronidase, methyl-glucuronide and fructuronate, under gratuitous conditions (without metabolic conversion of these two compounds), we corroborate the fact that both molecules are required simultaneously in order to derepress the enzyme synthesis to a maximum level. Structurally related analogs of the natural inducers, thiophenyl-glucuronide and mannonic amide respectively, were assayed in the wild type and suitable mutant strains of E. coli. The results are in agreement with the model where the dual negative regulation of the enzyme synthesis is exerted by two regulatory genes uidR and uxuR. The concerted action of mannonic amide and thiophenyl-glucuronide, which alone fail to induce significantly beta-glucuronidase synthesis, reveals that a cooperative effect of the two repressor molecules responsible for the complete blocking of the enzyme synthesis is occuring.

Drug Synergism↗
PubMed1976

The regulation of agarase production by resting cells of Cytophaga flevenis.

The regulation of the synthesis of extracellular agarase by Cytophaga flevensis was studied in resting-cell suspensions. Enzyme synthesis was strictly dependent on the presence of a suitable inducer. Enzyme production was maximal at 20 C in phosphate buffer pH 6.9 in the presence of 1.3 mM calcium chloride, 0.03% casamino acids and inducer. Enzyme production was virtually the same at 15 and 20 C, reduced to 50% at 25 C and was not detectable at 30 C. It was highly stimulated by the presence of 0.03% of casamino acids in the incubation mixture and was also favoured by the presence of 1.3 mM calcium ions. Of a variety of compounds tested, only melibiose or neoagaro-oligosaccharides were effective inducers. Among the neoagaro-oligosaccharides, neoagarotetraose was the best inducer. At higher concentrations of inducer compounds catabolite repression of enzyme synthesis was apparent. This was also found when glucose was added to the incubation mixture. This repression was not relieved by the addition of cyclic AMP. Indications were found that the excretion process was limiting the rate of production of extracellular enzyme

Agar↗
PubMed1969

Regulation of enzyme synthesis in the aromatic amino acid pathway of Bacillus subtilus.

The control of the synthesis of certain key enzymes of aromatic amino acid biosynthesis was studied. Tyrosine represses the first enzyme of the 3-deoxy-d-arabino heptulosonic acid 7-phosphate pathway, DAHP synthetase, as well as shikimate kinase and chorismate mutase about fivefold in cultures grown under conditions limiting the synthesis of the aromatic amino acids. A mixture of tyrosine and phenylalanine represses twofold further. Tryptophan does not appear to be involved in the control of these enzymes. The specific activity of at least one early enzyme, dehydroquinase, remains essentially constant under a variety of nutritional supplementations. Two enzymes in the terminal branches are repressed by the amino acids they help to synthesize: prephenate dehydrogenase can be repressed fourfold by tyrosine, and anthranilate synthetase can be repressed over 200-fold by tryptophan. There is no evidence that phenylalanine represses prephenate dehydratase. Regulatory mutants have been isolated in which various enzymes of the pathway are no longer repressible. One class is derepressed for several of the prechorismate enzymes, as well as chorismate mutase and prephenate dehydrogenase. In another mutant, several enzymes of tryptophan biosynthesis are no longer repressible. Thus, the rate of synthesis of enzymes at every stage of the pathway is under control of various aromatic amino acids. Tyrosine and phenylalanine control the synthesis of enzymes involved in the synthesis of the three aromatic amino acids. Each terminal branch is under the control of its end product.

Arabinose↗
PubMed1977

[Phospholipid composition of E. coli cells and membranes under repression and derepression of alkaline phosphatase biosynthesis].

Lipid composition of E. coli membranes and cells in conditions of repression, derepression and constitutive synthesis of alkaline phosphatase is studied. The identity of qualitative composition of phospholipids and neutral lipids in these conditions is demonstrated. Derepressed and constitutive enzyme syntheses are correlating, a certain increase of phosphatidylglycerol in the total phospholipid pool being more pronounced in cells, than in membranes. The enzyme synthesis correlates also with the increase of 14C-label incorporation into lipids.

Alkaline Phosphatase↗
PubMed1995

Repression of the pea lipoxygenase gene loxg is associated with carpel development.

A cDNA clone (loxg) corresponding to a gene repressed during carpel development has been isolated from a cDNA library of unpollinated carpels induced to grow by treatment with gibberellic acid (GA3). The sequences of loxg cDNA and the deduced polypeptide have a high similarity with legume type 2 lipoxygenases, especially with Phaseolus lox1 (78.5% similarity at the protein level) and pea and soybean lox3 (83.6% and 85.4%, respectively). loxg expression is constant in unstimulated carpels but it decreases in carpels induced to keep growing by fertilization or hormone treatment. A similar pattern of repression was observed in lipoxygenase activity of pea and tomato carpels. In situ hybridization studies showed that loxg mRNAs are present in the endocarp and the mesocarp of pea pods; no loxg expression was detectable either in the pod exocarp or in the ovules. Loxg is also expressed in other young growing tissues, especially in flower organs. Nevertheless, the natural pattern of flower and fruit development is associated with loxg repression.

Amino Acid Sequence↗
PubMed1975

Catabolite repression of Pseudomonas aeruginosa amidase: the effect of carbon source on amidase synthesis.

Synthesis of the Pseudomonas aeruginosa aliphatic amidase was repressed severely by succinate and malate and less severely by glucose, acetate or lactate. Amidase synthesis in inducible and constitutive strains was stimulated by cyclic AMP, which also gave partial relief to catabolite repression produced by the addition of lactate to cultures growing in pyruvate medium. Mutants which were resistant to catabolite repression were isolated from succinate+lactamide medium.

Acetamides↗
PubMed1994

Sequences involved in growth-phase-dependent expression and glucose repression of a Streptomyces alpha-amylase gene.

In glycerol-grown, but not in glucose-grown cultures, expression in Streptomyces lividans TK24 of the cloned alpha-amylase gene (aml) of Streptomyces limosus is switched on toward the end of exponential growth. During this period, aml expression is further inducible by maltotriose. We showed that a 378 bp fragment, extending from position -204 through to +174 (relative to the transcriptional start site), included cis-acting sequences involved in aml regulation. When this fragment was present on a multicopy plasmid, the growth-phase-dependent aml expression conferred by a DNA fragment cloned on a compatible low-copy-number plasmid was greatly enhanced, as if negative regulators were being titrated. A study of the regulation of aml expression in variants with deletions in the aml promoter region indicated that a direct repeat (DR) between positions -124 and -106 (relative to the transcriptional start site) and an inverted repeat (IR) between positions +9 and +24 were good candidates for secondary and primary operator sites, respectively. Deletion of a 29 bp fragment containing the IR rendered aml expression partly growth-phase-independent, resistant to glucose repression, and insensitive to maltotriose induction.

Amino Acid Sequence↗