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PubMed2000

Regulation of carbon catabolism in Bacillus species.

The gram-positive bacterium Bacillus subtilisis capable of using numerous carbohydrates as single sources of carbon and energy. In this review, we discuss the mechanisms of carbon catabolism and its regulation. Like many other bacteria, B. subtilis uses glucose as the most preferred source of carbon and energy. Expression of genes involved in catabolism of many other substrates depends on their presence (induction) and the absence of carbon sources that can be well metabolized (catabolite repression). Induction is achieved by different mechanisms, with antitermination apparently more common in B. subtilis than in other bacteria. Catabolite repression is regulated in a completely different way than in enteric bacteria. The components mediating carbon catabolite repression in B. subtilis are also found in many other gram-positive bacteria of low GC content.

Bacillus↗
PubMed1980

[Cloning of threonine operon genes in Escherichia coli cells].

A set of hybrid plasmids carrying Escherichia coli threonine genes was obtained and cloned. The plasmid pBR322 was used as a vehicle. The genetic and restriction analyses showed that genes thrA and thrB were placed between SalGI and EcoRI sites on the 2.6 megadaltons DNA region. The transcription of threonine operon genes inserted in the hybrid plasmids is under the control of its own promoter. The copy number of hybrid plasmids was reverse proportional to their molecular weight and did not depend on the replicon number. Amplification of genes of threonine operon by hybrid plasmids led to 20-25-fold increase of homoserine dehydrogenase activity, encoded by thrA gene. The expression of this gene, incorporated in hybrid plasmids, was repressed by the addition of threonine and isoleucine in the culture medium.

Alcohol Oxidoreductases↗
PubMed1974

Rapid loss of translatable messenger RNA of phosphoenolpyruvate carboxykinase during glucose repression in liver.

The rate of synthesis of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) in rat liver decreased with a half-life of 30 min after fasted rats were refed either a chow diet or glucose. A requirement for both glucose and insulin to bring about this rapid deinduction was shown, as well as the ability of dibutyryl adenosine 3':5'-cyclic monophosphate to block the decrease in enzyme synthesis. Estimates of the stability of messenger RNA of phosphoenolpyruvate carboxykinase were made by using the inhibitors actinomycin D and cordycepin to block further messenger RNA synthesis, and then measuring the decrease in specific enzyme synthesis. It is suggested that the use of actinomycin D yields an overestimation of the template stability. The results with cordycepin imply that the enzyme messenger RNA has a short half-life of approximately 1 hr. Thus, it is possible that deinduction may proceed by way of a decrease in messenger RNA production, leading to a rapid fall in the synthesis of phosphoenolpyruvate carboxykinase.

Animals↗
PubMed1974

Regulation of maltodextrin phosphorylase synthesis in Escherichia coli by cyclic adenosine 3', 5'-monophosphate and glucose.

Cyclic adenosine 3', 5'-monophosphate (AMP) stimulates maltodextrin phosphorylase synthesis in Escherichia coli cells induced with maltose. A maximal effect occurs at 2 to 3 mM cyclic AMP. The action of cyclic AMP is specific, inasmuch as adenosine triphosphate, 3'-AMP, 5'-AMP, adenosine, and dibutyryl cyclic AMP are inactive. Glucose, alpha-methyl glucoside, 2-deoxyglucose, and pyridoxal 5'-phosphate repress maltodextrin phosphorylase synthesis. This repression is reversed by cyclic AMP. The action of cyclic AMP appears to be at the transcriptional level, since cyclic AMP fails to stimulate phosphorylase production in induced cells in which messenger ribonucleic acid synthesis has been arrested by rifampin or by inducer removal. The two other enzymes involved in the metabolism of maltose, amylomaltase and maltose permease, are also induced in this strain of E. coli and affected by glucose and cyclic AMP in a manner similar to phosphorylase.

Adenosine↗
PubMed1989

Effect of glucose on isocitrate lyase in Phycomyces blakesleeanus.

Repression of the synthesis of isocitrate lyase by glucose and/or induction of the synthesis of isocitrate lyase by acetate in Phycomyces blakesleeanus were demonstrated. Both glycerol and ethanol failed to induce isocitrate lyase activity. Furthermore, glucose appeared to cause an in vivo catabolite inactivation of the derepressed enzyme. Isocitrate lyase was inactivated both reversibly and irreversibly by glucose.

Acetates↗
PubMedDate not supplied

[Photoinduction of carotenoid synthesis by Neurospora crassa on different structural and functional states of nitrate reductase].

In order to clarify the role of nitrate reductase as a potential photoreceptor, the ability of N. crassa mycelial cells for light-dependent accumulation of carotenoid pigments has been studied. The repression of the nitrate reductase synthesis by ammonium ions has been found not to influence the rate of the photoinduced carotenogenesis. The mutant experiments have shown that damage to the structural integrity of the nitrate reductase molecule, e, g., disintegrated synthesis of the protein fragment of the enzyme molecule (mutants nit-2 and nit-3) or the molybdenum coenzyme (mutant nit-1) does not affect the activity of the photoregulatory system of N. crassa. Thus, nitrate reductase is not a necessary component of the photoregulatory mechanism of N. crassa responsible for the synthesis of carotenoids.

Carotenoids↗
PubMed1971

Involvement of threonine deaminase in multivalent repression of the isoleucine-valine pathway in Saccharomyces cerevisiae.

A strain (MAR33) of Saccharomyces cerevisiae containing a threonine deaminase [L-threonine hydrolyase (deaminating) EC 4.2.1.16] with decreased feedback sensitivity has been shown to have a specific activity of acetohydroxy acid synthetase higher than that of the parent strain (MD11) when both are grown on minimal medium. When strain MAR33 is grown on minimal medium supplemented only with isoleucine, the specific activity of the synthetase is reduced to that found in the parent strain. Another strain, D106-1A, contains a nonsense mutation in the middle of the gene for threonine deaminase. When this strain is grown on minimal medium containing appropriate supplements (which include a nonrepressing concentration of isoleucine), or on minimal medium supplemented with isoleucylglycine (which acts as a limiting source of isoleucine), acetohydroxy acid synthetase remains repressed. Leucine limitation causes partial derepression. With the reversion of the nonsense mutation, either intragenically or via a suppressor for the mutation, partial derepression of the synthetase returns. When D106-1A is diploidized with either M15, a mutant lacking the synthetase, or MD9, a strain containing the enzyme, normal, partially derepressed, values for this enzyme are found. This indicates that threonine deaminase is necessary for derepression, and that it possibly acts as an inducer.

Culture Media↗
PubMed1988

Thialysine- and selenalysine-resistance in a E. coli mutant.

A thialysine-resistant mutant of E. coli strain KL16 also shows a lower sensitivity to selenalysine, the lysine analog containing selenium. No difference between the mutant and the parental strain has been shown regarding the affinities of the transport systems and the lysyl-tRNA synthetase for selenalysine, thialysine and lysine as well as the inhibitory effects of these three aminoacids on the activity of the lysine biosynthetic pathway. A marked difference between the two strains has been evidenced in the AK III repression: in the mutant the repression by selenalysine, thialysine and lysine is much lower than in the parental strain.

Aspartate Kinase↗
PubMed1974

Regulation of aconitase synthesis in Bacillus subtilis: induction, feedback repression, and catabolite repression.

The synthesis of aconitase in Bacillus subtilis wild-type and different citric acid cycle mutants has been studied and the influence of various growth conditions examined. Aconitase is induced by citrate and precursors of citrate and repressed by glutamate. Induction and repression counteract each other, and at equimolar concentrations of citrate and glutamate, aconitase synthesis is unaffected. Induction by citrate can partly overcome catabolite repression of aconitase. Isocitrate dehydrogenase show endogenous induction of aconitase due to citrate accumulation. Leaky mutants defective in citrate synthase and aconitase cannot be induced by citrate, which indicates that they carry a regulatory mutation. The complex regulation of aconitase is discussed with reference to the participation of this enzyme in glutamate biosynthesis and energy metabolism.

Aconitate Hydratase↗
PubMed1996

Krüppel-associated box-mediated repression of RNA polymerase II promoters is influenced by the arrangement of basal promoter elements.

The evolutionarily conserved Krüppel-associated box (KRAB) is present in the N-terminal regions of more than one-third of all Krüppel-class zinc finger proteins. Recent experiments have demonstrated that the KRAB-A domain tethered to a promoter DNA by connecting to heterologous DNA-binding protein domain or targeted to a promoter-proximal RNA sequence acts as a transcriptional silencing of RNA polymerase II promoters. Here we show that expression of KRAB domain suppresses in vivo the activating function of various defined activating transcription factors, and we demonstrate that the KRAB domain specifically silences the activity of promoters whose initiation is dependent on the presence of a TATA box. Promoters whose accurate transcription initiation is directed by a pyrimidine-rich initiator element, however, are relatively unaffected. We also report in vitro transcription experiments indicating that the KRAB domain is able to repress both activated and basal promoter activity. Thus, the KRAB domain appears to repress the activity of certain promoters through direct communication with TATA box-dependent basal transcription machinery.

Base Sequence↗
PubMed2001

Transcriptional regulation of the yeast gmp synthesis pathway by its end products.

AMP and GMP are synthesized from IMP by specific conserved pathways. In yeast, whereas IMP and AMP synthesis are coregulated, we found that the GMP synthesis pathway is specifically regulated. Transcription of the IMD genes, encoding the yeast homologs of IMP dehydrogenase, was repressed by extracellular guanine. Only this first step of GDP synthesis pathway is regulated, since the latter steps, encoded by the GUA1 and GUK1 genes, are guanine-insensitive. Use of mutants affecting GDP metabolism revealed that guanine had to be transformed into GDP to allow repression of the IMD genes. IMD gene transcription was also strongly activated by mycophenolic acid (MPA), a specific inhibitor of IMP dehydrogenase activity. Serial deletions of the IMD2 gene promoter revealed the presence of a negative cis-element, required for guanine regulation. Point mutations in this guanine response element strongly enhanced IMD2 expression, also making it insensitive to guanine and MPA. From these data, we propose that the guanine response element sequence mediates a repression process, which is enhanced by guanine addition, through GDP or a GDP derivative, and abolished in the presence of MPA.

Adenosine Monophosphate↗
PubMed1993

A lowered concentration of cAMP receptor protein caused by glucose is an important determinant for catabolite repression in Escherichia coli.

A decreased intracellular concentration of cAMP is insufficient to account for catabolite repression in Escherichia coli. We show that glucose lowers the amount of cAMP receptor protein (CRP) in cells. A correlation exists between CRP and beta-galactosidase levels in cells growing under various conditions. Exogenous cAMP completely eliminates catabolite repression in CRP-overproducing cells, while it does not fully reverse the effect of glucose on beta-galactosidase expression in wild-type cells. When the CRP concentration is reduced by manipulating the crp gene, beta-galactosidase expression decreases in proportion to the concentration of CRP. These findings indicate that the lowered concentration of CRP caused by glucose is one of the major factors for catabolite repression. We propose that glucose causes catabolite repression by lowering the intracellular levels of both CRP and cAMP.

Bacterial Proteins↗
PubMed1994

The repression of listeriolysin O expression in Listeria monocytogenes by the phenolic beta-D-glucoside, arbutin.

Expression of the listeriolysin O, a key virulence factor for Listeria monocytogenes, was monitored using a hlyA-luxAB transcriptional fusion. The phenolic beta-D-glucoside, arbutin, was found to repress the expression of the listeriolysin O at the level of transcription. In contrast, the structurally similar beta-glucoside salicin did not prevent expression of listeriolysin.

Arbutin↗
PubMed1971

Histidine regulation in Salmonella typhimurium. 8. Mutations of the hisT gene.

The hisT gene, one of six genes in which mutation causes derepression of the histidine operon in Salmonella typhimurium, is shown to code for a protein that is not essential for the growth of the bacteria. This is indicated by the characterization of particular classes of mutations in the hisT gene: amber mutations, frame-shift mutations, and temperature-sensitive mutations that affect repression but not growth. In addition, the class of semilethal mutations was selected for but not found.

Alanine↗
PubMed1980

Regulation of Klebsiella pneumoniae hut operons by oxygen.

We investigated the regulation of genes concerned with nitrogen metabolism by oxygen in the facultative anaerobe Klebsiella pneumoniae. We found oxygen to be required for the expression of the hut operons; the effect of O2 on the glutamine synthetase and urease was less pronounced than on the hut operons. Glutamine synthetase was transiently repressed during the transition from an aerobic to an anaerobic environment. Regulation of hut by O2 suppressed the effect of nitrogen limitation on the expression of these genes.

Enzyme Repression↗
PubMed1983

What is the function of nitrogen catabolite repression in Saccharomyces cerevisiae?

In contrast to the previously held notion that nitrogen catabolite repression is primarily responsible for the ability of yeast cells to use good nitrogen sources in preference to poor ones, we demonstrate that this ability is probably the result of other control mechanisms, such as metabolite compartmentation. We suggest that nitrogen repression is functionally a long-term adaptation to changes in the nutritional environment of yeast cells.

Allantoin↗