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PubMed2001

ADHII in Aspergillus nidulans is induced by carbon starvation stress.

In Aspergillus nidulans there are three NAD(+)-dependent alcohol dehydrogenases (ADHs) that are capable of utilizing ethanol as a substrate. ADHI is the physiological enzyme of ethanol catabolism and ADHIII is induced under conditions of anaerobiosis. The physiological role of ADHII (structural gene alcB) is unknown. We have measured beta-galactosidase in a transformant with an alcB::lacZ fusion and have shown that alcB is maximally expressed under conditions of carbon starvation. The behavior of the alcB::lacZ transformant suggests a hierarchy of repressing carbon sources characteristic of repression by the general carbon catabolite repressor protein, CreA, but in a creA(d)30 background the transformant shows only partial derepression of beta-galactosidase on 1% glucose compared to the creA+ strain. Our results suggest that, in addition to carbon catabolite repression acting via CreA, a CreA-independent mechanism is involved in induction of alcB on carbon starvation.

Alcohol Dehydrogenase↗
PubMed1998

Coupling physiology and gene regulation in bacteria: the phosphotransferase sugar uptake system delivers the signals.

In many bacteria a crucial link between metabolism and regulation of catabolic genes is based on the phosphotransferase sugar uptake system (PTS). We summarize the mechanisms of the signaling pathways originating from PTS and leading to regulation of transcription. A protein domain, called PTS regulation domain (PRD), is linked to many antiterminators and transcriptional activators and regulates their activity depending on its state of phosphorylation. Two sites can be phosphorylated in most PRDs: HPr-dependent modification at one site leads to activation while enzyme II dependent phosphorylation of the other site renders it inactive. In addition, PTS components are used to generate cofactors for regulators of transcription. The paradigm is the enzyme II dependent activity of adenylate cyclase determining the cyclic AMP level in Escherichia coli and thereby the activity of the catabolite activator protein. In many gram-positive bacteria catabolite repression is mediated by the catabolite control protein CcpA, which requires HPr Ser-46 phosphate as a cofactor to regulate transcription of catabolic genes. HPr Ser-46 phosphate is produced by HPr kinase, the activity of which is under metabolic control via the concentrations of glycolytic intermediates. These recent results establish a multifaceted regulatory role for PTS in addition to its well-established function in active sugar uptake.

Cyclic AMP↗
PubMed2004

Glucose kinase alone cannot be responsible for carbon source regulation in Streptomyces peucetius var. caesius.

Using an antibiotic enrichment procedure, eight mutants of Streptomyces peucetius var. caesius were isolated for their sensitivity to the glucose analogue 2-deoxyglucose (DOG), from a DOG-resistant strain (Dog(R)). These mutants (Dog(S)) and their parent strain were examined for growth sensitivity to DOG, glucose kinase (Glk) activity, glucose uptake, and sensitivity to repression by glucose and other catabolites derived from it. No correlation was found between Glk levels or glucose uptake and carbon catabolite repression (CCR) in these strains. However, the ratio of glucose uptake to Glk activity, and thus the flux through glycolysis, seemed responsible for this effect. Among several products of glucose catabolism tested, fructose-1,6-bis-phosphate and phosphoenolpyruvate showed significant repression of anthracycline formation. These compounds also reduced anthracycline formation in a Dog(R) mutant insensitive to glucose repression. Our data suggest that Glk alone is not sufficient to elicit CCR in this microorganism, and gives the first physiological evidence supporting the hypothesis that some products of glucose catabolism are involved in CCR in Streptomyces.

Antimetabolites↗
PubMed1971

Cyclic adenosine 3',5'-monophosphate during glucose repression in the rat liver.

Intragastric administration of glucose inhibits the induction of serine dehydratase and tyrosine aminotransferase by glucagon in rat liver, but has no effect on the increase in hepatic adenosine 3',5'-monophosphate resulting from administration of glucagon. Thus, glucose repression in mammalian liver, unlike catabolite repression in microorganisms, appears to operate independently of the amounts of cyclic nucleotide in the cells.

Animals↗
PubMed1963

INDUCTION AND REPRESSION OF L-ARABINOSE ISOMERASE IN PEDIOCOCCUS PENTOSACEUS.

Dobrogosz, Walter J. (University of Illinois, Urbana) and Ralph D. DeMoss. Induction and repression of l-arabinose isomerase in Pediococcus pentosaceus. J. Bacteriol. 85:1350-1355. 1963.-The inducible l-arabinose isomerase of Pediococcus pentosaceus can be rapidly and conveniently measured in whole-cell preparations by use of a standard colorimetric procedure originally developed for studies with cell-free enzyme preparations. The enzyme is measured by its ability to catalyze the isomerization of l-arabinose to l-ribulose. Whole cells suspended in a suitable buffer and pretreated with toluene were shown to exhibit this isomerase activity at a level comparable with that observed in cell-free enzyme preparations. Conditions for optimal induction of l-arabinose isomerase are described. In addition, it was determined that the formation of this enzyme is subject to repression by glucose, i.e., via catabolite repression.

Aldose-Ketose Isomerases↗
PubMed1968

Paradoxical effect of weak inducers on the lac operon of Escherichia coli.

Previously, we reported the existence of a group of compounds whose function in the regulation of the lac operon was "paradoxical" in that they acted as either inducers or repressors depending on the circumstances. We now show that this group of compounds does not repress the lac operon by catabolite repression, transient repression, or by preventing the uptake of inducers. A model is presented which shows that "paradoxical" behavior is to be expected if a weak inducer is present at a concentration that is high relative to its binding affinity for the regulatory macromolecule. This model depends on the assumptions that the regulatory macromolecule is an allosteric protein which undergoes a transition between two conformational states and that the rate of enzyme synthesis depends on the fraction of protein molecules in each state. The previous observations on the responses of lac regulatory mutants to weak inducers have been extended to a series of such mutants. Weak inducers repress beta-galactosidase synthesis in several i(-) mutants. When this happens, enzyme synthesis can be reinduced by using a strong inducer such as isopropyl-beta-d-thiogalactoside. These compounds induce operator constitutives and the i(t) mutant more easily than they induce a wild-type strain.

Enzyme Induction↗
PubMed2025

Gfa1 (glutamine fructose-6-phosphate aminotransferase) is essential for Aspergillus fumigatus growth and virulence.

BACKGROUND: Aspergillus fumigatus, the primary etiological agent of invasive aspergillosis, causes over 1.8 million deaths annually. Targeting cell wall biosynthetic pathways offers a promising antifungal strategy. Gfa1, a rate-limiting enzyme in UDP-GlcNAc synthesis, plays a pivotal role in the hexosamine biosynthetic pathway (HBP). RESULTS: Deletion of gfa1 (Δgfa1) results in auxotrophy for glucosamine (GlcN) or N-acetylglucosamine (GlcNAc). Under full recovery (FR) conditions, where minimal medium is supplemented with 5 mM GlcN as the sole carbon source, the Δgfa1 mutant shows growth comparable to the wild-type (WT). However, when supplemented with 5 mM GlcN and 55 mM glucose, growth is partially repressed, likely due to carbon catabolite repression, a condition termed partial repression (PR). Under PR conditions, Δgfa1 exhibits compromised growth, reduced conidiation, defective germination, impaired cell wall integrity, and increased sensitivity to endoplasmic reticulum (ER) stress and high temperatures. Additionally, Δgfa1 demonstrates disruptions in protein homeostasis and iron metabolism. Transcriptomic analysis of the mutant under PR conditions reveals significant alterations in carbohydrate and amino acid metabolism, unfolded protein response (UPR) processes, and iron assimilation. Importantly, Gfa1 is essential for A. fumigatus virulence, as demonstrated in Caenorhabditis elegans and Galleria mellonella infection models. CONCLUSIONS: These findings underscore the critical role of Gfa1 in fungal pathogenicity and suggest its potential as a therapeutic target for combating A. fumigatus infections.

Aspergillus fumigatus↗
PubMed1984

Peptide antibiotic K-582 production in relation to amino acid metabolism in Metarrhizium anisopliae.

Formation of the basic antibiotic, K-582 was stimulated by supplying Metarrhizium anisopliae U-47 with several amino acids present in its structure. The addition of L-arginine to the basal medium resulted in the almost exclusive formation of K-582 B, while L-lysine increased K-582 A formation. Some carbon sources were observed to have effects similar to those obtained with the above mentioned amino acids. Furthermore, when L-arginine was added in excess to the basal medium, free gamma-hydroxyarginine, which is a major constituent of the antibiotic, accumulated extra- and intra-cellularly. Free gamma-hydroxyarginine isolated from the culture broth of this microorganism was the threo-L-isomer. K-582 formation was repressed by glycerol, which exerted catabolite repression of gamma-hydroxyarginine synthesis.

Amino Acids↗
PubMed1988

Redistribution of phosphate pools and the regulation of Escherichia coli adenylate cyclase activity.

The enzyme adenylate cyclase plays a key role in mediating the phenomenon of catabolite repression in Escherichia coli. The mechanism by which one sugar prevents the expression of the gene for another catabolite depends on the capacity of the cell to take up the sugar. Sugars that are most effective in the repression mechanism are those that are transported by the phosphoenolpyruvate-energized phosphotransferase system. The hypothesis presented here is that one or more of the proteins associated with this sugar transport system interact with adenylate cyclase and, when they are in their phosphorylated form, activate the enzyme, provided other factors that permit this activation are present. Another essential activator of adenylate cyclase is inorganic orthophosphate. When E. coli are starved for sugars, the pool of total phosphate is accounted for primarily as inorganic orthophosphate, ATP, phosphoenolpyruvate, and transport proteins in their phospho-forms, a condition that promotes activation of adenylate cyclase. When cells are exposed to sugars, the phosphate pool becomes drastically redistributed, such that the level of inorganic orthophosphate and transport phosphoproteins decreases markedly while the pool of sugar phosphate increases. This translation of the extracellular availability of carbon sources into an intracellular phosphate redistribution is the immediate event that is responsible for catabolite repression.

Adenylyl Cyclases↗
PubMed1997

Arabinoxylan degradation by fungi: characterization of the arabinoxylan-arabinofuranohydrolase encoding genes from Aspergillus niger and Aspergillus tubingensis.

The genes encoding the enzyme arabinoxylan arabinofuranohydrolase, which releases L-arabinose from arabinoxylan, have been cloned from the closely related fungi Aspergillus niger and Aspergillus tubingensis and were shown to be functional in A. niger. Integration of multiple copies in the genome resulted in over-expression of the enzymes. The arabinofuranohydrolases encoded comprise 332 amino acids and have 94% amino acid identity. Their primary structure is not related to those of other alpha-L-arabinofuranosidases, except for a low similarity with XYLC, a bacterial alpha-L-arabinofuranosidase from Pseudomonas fluorescens which acts on oat spelt xylan. The axhA expression pattern in A. niger differed from that of abfB, since it was strongly induced by birchwood xylan and much less by L-arabitol or L-arabinose. Furthermore, Northern analysis revealed that axhA expression was de repressed in creAd mutants and carbon catabolite repressed by D-glucose.

Amino Acid Sequence↗
PubMed2005

Evidence that Bacillus catabolite control protein CcpA interacts with RNA polymerase to inhibit transcription.

Summary Bacilluscatabolite control protein (CcpA) mediates carbon catabolite repression (CCR) by controlling expression of catabolite responsive (CR) genes or operons through interaction with catabolite responsive elements (cres) located within or outside of CR promoters. Here, we investigated how CcpA inhibits the transcription of CR promoters in vitro. CcpA has different affinities for different cres, but this does not correlate with its ability to inhibit transcription. In the amyE promoter, which overlaps a CcpA binding site (amyE cre centred at +4.5), CcpA does not prevent RNA polymerase (RNAP) binding to the promoter; it may even interact with RNAP. Inserting non-integral turns of helix (1.5 and 2.5) between the amyE promoter (-10 hexamer) and the amyE cre relieved CCR of amyE expression. In the xyl operon, despite the downstream location of its cre (a major cre centred at +130.5), CcpA blocked transcription initiation, not elongation (roadblock) at the site of the cre. Taken together, our results strongly suggest that CcpA requires interactions with RNAP to inhibit transcription.

ATP-Binding Cassette Transporters↗
PubMed1989

Induction and metabolite regulation of levanase synthesis in Bacillus subtilis.

Levanase expression in Bacillus subtilis was studied by using transcriptional and translational fusions. It was shown that the degradative products of levan or inulin and low concentrations of fructose were able to induce levanase expression. In the wild-type strain and in a constitutive overproducing sacL mutant, levanase synthesis was repressed by glucose or fructose. This catabolite repression was partially abolished in the derepressed alpha-amylase gra-26 mutant. The levanase gene (sacC) appears to be the distal gene of an operon transcribed from a fructose-inducible promoter. Deletion mapping experiments and primer extension analysis revealed a transcriptional start point located 2.7 kilobases upstream from the sacC gene. Two constitutive sacL mutations were shown to be closely linked by transformation to the sacC gene. The sacL6 and sacL8 mutations were mapped in the promoter-proximal region of the operon.

Amino Acid Sequence↗
PubMed1989

[Regulation in the expression of alpha-galactosidase gene in raf operon in Escherichia coli].

The alpha-galactosidase, coded for by the first structural gene rafA in the plasmid determined raf operon was an inducible enzyme. In contrast to lac or mel operon, raf operon has more strict structural specificity for inducers. The enzyme can be induced by melibiose and raffinose, or weakly by D-galactose, but not by structurally related sugars such as lactose, PNPG etc.. The alpha-galactosidase forming capacity as function of growth curve reached a single peak at the end of the logarithmic phase of the growth. The structure and regulation of raf operon is similar to those of lac operon. The repressormor-mediated negative control plays a major role in the regulation of raf operon, and cAMP-CAP mediated positive control is also involved in the regulation. When 0.4% glucose was added into the medium with other carbon sources, the expression of the enzyme was repressed by 2-3 fold. Transient catabolite repression has been observed neither in inducible nor constitutive alpha-galactosidase expression. Based on alpha-galactosidase assay, in mutant strains CA8306(cya) and CA8445 (cya, crp) the expression level of raf operon was only 9% and 2.5% of that in wild type strain respectively. The glucose effect or the repression in cya mutant can be abolished by 1-5 mmol cAMP. The constitutive alpha-galactosidase expression in cya and cry double mutant (CA8445) remains repressible by glucose, but irreversible by cAMP, suggesting cAMP-CAP complex is not the exclusive mediator of the catablite repression.(ABSTRACT TRUNCATED AT 250 WORDS)

Escherichia coli↗
PubMed1999

Effect of dilution rate, cellobiose and ammonium availabilities on Clostridium cellulolyticum sporulation.

The nutritional and physiological factors affecting sporulation of Clostridium cellulolyticum were studied using steady-state continuous cultures grown in both complex and synthetic media. Under cellobiose limitation, the probability that cells will sporulate appears to be directly related to the growth rate. In complex medium, the highest percentage of sporulation was 20% at a dilution rate of 0.015 h-1 whereas in synthetic medium it was 10% at 0.035 h-1. In both media, when the dilution rate was either higher or lower the percentage of sporulation decreased by between 2% and 4%. At low dilution rates, endospore formation was repressed under cellobiose-sufficient concentrations, suggesting catabolite repression by cellobiose. Furthermore, the concentration of ammonium was important in determining the percentage of sporulation, as ammonium limitation induced extensive sporulation at low growth rates even in an excess of cellobiose. The sporulation process is not triggered when cells are cellobiose-exhausted both in complex and synthetic media. These data suggest that, in C. cellulolyticum, an exogenous supply of carbon is required throughout the sporulation process. In the experimental conditions used in this work, no relationship between glycogen accumulation or glycogen mobilization and endospore formation was detected in C. cellulolyticum.

Biomass↗
PubMed2003

A hexose transporter homologue controls glucose repression in the methylotrophic yeast Hansenula polymorpha.

Peroxisome biogenesis and synthesis of peroxisomal enzymes in the methylotrophic yeast Hansenula polymorpha are under the strict control of glucose repression. We identified an H. polymorpha glucose catabolite repression gene (HpGCR1) that encodes a hexose transporter homologue. Deficiency in GCR1 leads to a pleiotropic phenotype that includes the constitutive presence of peroxisomes and peroxisomal enzymes in glucose-grown cells. Glucose transport and repression defects in a UV-induced gcr1-2 mutant were found to result from a missense point mutation that substitutes a serine residue (Ser(85)) with a phenylalanine in the second predicted transmembrane segment of the Gcr1 protein. In addition to glucose, mannose and trehalose fail to repress the peroxisomal enzyme, alcohol oxidase in gcr1-2 cells. A mutant deleted for the GCR1 gene was additionally deficient in fructose repression. Ethanol, sucrose, and maltose continue to repress peroxisomes and peroxisomal enzymes normally and therefore, appear to have GCR1-independent repression mechanisms in H. polymorpha. Among proteins of the hexose transporter family of baker's yeast, Saccharomyces cerevisiae, the amino acid sequence of the H. polymorpha Gcr1 protein shares the highest similarity with a core region of Snf3p, a putative high affinity glucose sensor. Certain features of the phenotype exhibited by gcr1 mutants suggest a regulatory role for Gcr1p in a repression pathway, along with involvement in hexose transport.

Alcohol Oxidoreductases↗
PubMed1968

Requirements for macromolecular synthesis in the establishment of beta-galactosidase repression in zygotes.

Inhibitors of protein synthesis do not consistently prevent formation of the lac operon repressor, according to several published reports, although direct evidence indicates that the repressor is a protein. Inhibition of ribonucleic acid (RNA) synthesis has never been shown to block lactose repression. These results have raised the possibility that repressor is synthesized in some unusual fashion. We have studied the effect of various inhibitors upon the establishment of repression in zygotes, utilizing conditions which minimize catabolite repression. Inhibition of protein synthesis by either chloramphenicol treatment or tryptophan deprivation blocked repressor formation in our experiments. Sodium borate and 6-azauracil are compounds reported to be specific inhibitors of RNA synthesis, and their behavior in control experiments is consistent with this specificity. Both delayed the establishment of repression. Thymine deprivation, either by starvation of a thymine auxotroph or by treatment with 5-fluorodeoxyuridine, did not delay the onset of repression. We conclude that repressor formation requires RNA synthesis and probably utilizes the usual protein-forming mechanisms.

Aminopterin↗
PubMed2002

Global control of sugar metabolism: a gram-positive solution.

Bacteria utilise carbon sources in a strictly controlled hierarchical manner for which they have developed global control mechanisms that govern and coordinate carbon source-specific regulation. This is achieved via carbon catabolite repression (CCR), which is the result of global transcriptional control and inducer exclusion. A common mechanism for transcriptional control has evolved within the group of low-GC Gram-positive bacteria, including lactic acid bacteria. The seryl-phosphorylated form of the phosphotransferase HPr (HPr-ser-P) mediates CCR in concert with the pleiotropic regulator CcpA (catabolite control protein) by repressing or activating catabolite-controlled genes. HPr-ser-P can concomitantly trigger inducer exclusion by inhibition of carbohydrate-specific permeases. Histidyl-phosphorylated HPr (HPr-his P) is required for the transport of many carbon sources by the phosphotransferase system (PTS). In addition, HPr-his P controls carbohydrate-specific regulators and catabolic enzymes by phosphorylation. Thus, the ratio of HPr-his P/HPr-ser-P determines utilisation of a particular carbon source. This ratio is mainly adjusted by the bifunctional HPr kinase/phosphatase (HPrK/P), which itself is controlled by the metabolic state of the cell. As a result, the information about the metabolic state of the cell is combined with signals scoring the availability of carbon sources to fine-tune the expression of catabolic genes with the goal to optimise growth rate in any given mixture of nutrients. This review summarises the current understanding of carbon catabolite regulation in low-GC Gram-positive bacteria with special emphasis on lactic acid bacteria.

Glucose↗