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PubMedDate not supplied

[Isoelectric characterization of extracellular polygalacturanases of various Aspergillus alliaceus strains].

The composition of pectin hydrolase complexes produced by various Aspergillus alliaceus strains was studied under the conditions of induction, catabolite repression, or constitutive synthesis. The strains were found similar in terms of the polygalacturonase spectrum and different with regard to the levels of endo- and exoenzyme activities. The analysis of the zymograms of inducible polygalacturonases revealed that all tested cultures contained at least 24 molecular forms of polygalacturonase. Taking into account only the three molecular forms typical of all analyzed strains of A. alliaceus with pI values of 5.7, 5.9, and 6.3, one can use the spectrum of constitutive, catabolite repression-resistant polygalacturonases as an additional taxonomic species criterion.

Aspergillus↗
PubMed2005

How seryl-phosphorylated HPr inhibits PrfA, a transcription activator of Listeria monocytogenes virulence genes.

Listeria monocytogenes PrfA, a transcription activator for several virulence genes, including the hemolysin-encoding hly, is inhibited by rapidly metabolizable carbon sources (glucose, fructose, etc.). This inhibition is not mediated via the major carbon catabolite repression mechanism of gram-positive bacteria, since inactivation of the catabolite control protein A (CcpA) did not prevent the repression of virulence genes by the above sugars. In order to test whether the catabolite co-repressor P-Ser-HPr might be involved in PrfA regulation, we used a Bacillus subtilis strain (BUG1199) containing L. monocytogenes prfA under control of pspac and the lacZ reporter gene fused to the PrfA-activated hly promoter. Formation of P-Ser-HPr requires the bifunctional HPr kinase/phosphorylase (HprK/P), which, depending on the concentration of certain metabolites, either phosphorylates HPr at Ser-46 or dephosphorylates P-Ser-HPr. The hprKV267F allele codes for an HprK/P leading to the accumulation of P-Ser-HPr, since it has normal kinase, but almost no phosphorylase activity. Interestingly, introducing hprKV267F into BUG1199 strongly inhibited transcription activation by PrfA. Preventing the accumulation of P-Ser-HPr in the hprKV267F mutant by replacing Ser-46 in HPr with an alanine restored PrfA activity, while ccpA inactivation had no effect. Interestingly, disruption of ccpA in the hprK wild-type strain BUG1199 also led to inhibition of PrfA. The lowered lacZ expression in the ccpA strain is probably also due to elevated amounts of P-Ser-HPr, since it disappeared when Ser-46 in HPr was replaced with an alanine. To carry out its catalytic function in sugar transport, HPr of the phosphotransferase system (PTS) is also phosphorylated by phosphoenolpyruvate and enzyme I at His-15. However, P-Ser-HPr is only very slowly phosphorylated by enzyme I, which probably accounts for PrfA inhibition. In agreement with this concept, disruption of the enzyme I- or HPr-encoding genes also strongly inhibited PrfA activity. PrfA activity therefore seems to depend on a fully functional PTS phosphorylation cascade.

Amino Acid Substitution↗
PubMed1975

On the regulation of adenosine 3', 5'-monophosphate synthesis in bacteria. I. Effect of carbon source variation on cyclic AMP synthesis in Escherichia coli B/r.

1. The effect of carbon source variation in bacterial growth media on their growth rate, inducible enzyme and cyclic AMP synthesis was examined: an inverse relationship between the culture's growth rate and its differential rate of inducible enzyme (tryptophanase and beta-galactosidase), and cyclic AMP synthesis was found. 2. The effect of the culture's growth phase on its sensitivity or resistance to glucose catabolite repression was determined in the wild type and a catabolite insensitive mutant (ABDROI): the wild type's sensitivity to glucose repression was not affected, whereas the insensitivity of the mutant was found to be limited to its early logarithmic phase of growth. At late log, or stationary phase, the mutant was found to be sensitive to glucose repression. 3. Examination of the kinetics of glucose uptake by the mutant, using alpha-[1 4-C] methyl-glucoside showed evidence for two transport systems each with a different affinity to glucose. A low affinity transport system (apparent Km of 3.4-10-minus 5 M) which appears mostly at the early logarithmic phase of growth. A high affinity transport system (apparent Km of 1.2-10-minus 5 M) which appears mostly at the late log and stationary phases of growth. 4. The effect of the culture density variation on its sensitivity to glucose repression showed that sensitivity to glucose catabolic repression is primarily a reflection of the formation of an allosteric effector molecule between glucose and its specific transport molecule which in turn regulates the activity of the adenylate cyclase.

Allosteric Regulation↗
PubMedDate not supplied

[Molecular mechanisms of catabolic repression in yeast].

Modern data on the molecular mechanism of glucose (catabolite) repression in yeast are reviewed. Characteristics of the key components of the repression cascade, as well as accepted models of their regulation by glucose are presented.

Forecasting↗
PubMed2006

Molecular cloning and characterization of two intracellular beta-glucosidases belonging to glycoside hydrolase family 1 from the basidiomycete Phanerochaete chrysosporium.

cDNAs encoding two glycoside hydrolase family 1 beta-glucosidases (BGL1A and BGL1B) were cloned from the basidiomycete Phanerochaete chrysosporium, and the substrate specificities of the recombinant enzymes and the expression patterns of the two genes were investigated in relation to cellobiose metabolism by the fungus. The cDNA sequences contained open reading frames of 1,389 base pairs (bp) (bgl1A) and 1,623 bp (bgl1B), encoding 462 and 530 amino acids, respectively. Although high sequence identity (65%) was observed between the deduced amino acid sequences of the two enzymes, an apparent difference was observed at the C-terminal region: BGL1B has a 63-amino acid extension, which has no similarity with any known protein. Both recombinant enzymes expressed in Escherichia coli showed hydrolytic activity towards several beta-glycosidic compounds. However, the substrate recognition patterns of the two enzymes were quite different from each other. In particular, cellobiose was hydrolyzed more effectively by BGL1B than by BGL1A. The expression of the two genes in the fungus was monitored by reverse transcription-PCR, which showed that bgl1A was expressed constitutively in both glucose- and cellobiose-containing culture, whereas bgl1B was expressed in cellobiose culture but was repressed in glucose culture, possibly because of carbon catabolite repression. We conclude that BGL1B contributes to cellobiose metabolism during cellulose degradation by P. chrysosporium.

Amino Acid Sequence↗
PubMedDate not supplied

Cra and the control of carbon flux via metabolic pathways.

The catabolite repressor-activator (Cra) protein controls the direction of carbon flux through metabolic pathways in enteric bacteria. Cra binds to the control regions of target genes and exerts a negative effect on the expression of genes encoding glycolytic and Entner-Doudoroff enzymes, while exerting a positive effect on genes encoding Krebs cycle, glyoxylate shunt and gluconeogenic enzymes. Cra mediates cyclic AMP-independent catabolite repression of positively Cra-regulated genes and catabolite activation of negatively Cra-controlled genes.

Bacteria↗
PubMed2003

Functional and comparative genomic analyses of an operon involved in fructooligosaccharide utilization by Lactobacillus acidophilus.

Lactobacillus acidophilus is a probiotic organism that displays the ability to use prebiotic compounds such as fructooligosaccharides (FOS), which stimulate the growth of beneficial commensals in the gastrointestinal tract. However, little is known about the mechanisms and genes involved in FOS utilization by Lactobacillus species. Analysis of the L. acidophilus NCFM genome revealed an msm locus composed of a transcriptional regulator of the LacI family, a four-component ATP-binding cassette (ABC) transport system, a fructosidase, and a sucrose phosphorylase. Transcriptional analysis of this operon demonstrated that gene expression was induced by sucrose and FOS but not by glucose or fructose, suggesting some specificity for nonreadily fermentable sugars. Additionally, expression was repressed by glucose but not by fructose, suggesting catabolite repression via two cre-like sequences identified in the promoter-operator region. Insertional inactivation of the genes encoding the ABC transporter substrate-binding protein and the fructosidase reduced the ability of the mutants to grow on FOS. Comparative analysis of gene architecture within this cluster revealed a high degree of synteny with operons in Streptococcus mutans and Streptococcus pneumoniae. However, the association between a fructosidase and an ABC transporter is unusual and may be specific to L. acidophilus. This is a description of a previously undescribed gene locus involved in transport and catabolism of FOS compounds, which can promote competition of beneficial microorganisms in the human gastrointestinal tract.

ATP-Binding Cassette Transporters↗
PubMed1982

DHA system mediating aerobic and anaerobic dissimilation of glycerol in Klebsiella pneumoniae NCIB 418.

In Klebsiella pneumoniae NCIB 418, the pathways normally responsible for aerobic growth on glycerol and sn-glycerol 3-phosphate (the glp system) are superrepressed. However, aerobic growth on glycerol can take place by the intervention of the NAD-linked glycerol dehydrogenase and the ATP-dependent dihydroxyacetone kinase of the dha system normally inducible only anaerobically by glycerol or dihydroxyacetone. Conclusive evidence that the dha system is responsible for both aerobic and anaerobic dissimilation of glycerol was provided by a Tn5 insertion mutant lacking dihydroxyacetone kinase. An enzymatically coupled assay specific for this enzyme was devised. Spontaneous reactivation of the glp system was achieved by selection for aerobic growth on sn-glycerol 3-phosphate or on limiting glycerol as the sole carbon and energy source. However, the expression of this system became constitutive. Aerobic operation of the glp system highly represses synthesis of the dha system enzymes by catabolite repression.

Aerobiosis↗
PubMed1990

Beta-glucoside permease represses the bgl operon of Escherichia coli by phosphorylation of the antiterminator protein and also interacts with glucose-specific enzyme III, the key element in catabolite control.

The beta-glucoside (bgl) operon of Escherichia coli is subject to both positive control by transcriptional termination/antitermination and negative control by the beta-glucoside-specific transport protein, an integral membrane protein known as enzyme IIBgl. Previous results led us to speculate that enzyme IIBgl exerts its negative control by phosphorylating and thereby inactivating the antiterminator protein, BglG. Specifically, our model postulated that the transport protein enzyme IIBgl exhibits protein-phosphotransferase activity in the absence of beta-glucosides. We now present biochemical evidence that the phosphorylation of protein BglG does indeed occur in vivo and that it is accompanied by the loss of antitermination activity. BglG persists in the phosphorylated state in the absence of beta-glucosides but is rapidly dephosphorylated when beta-glucosides become available for transport. Our data also suggested specific interactions between the beta-glucoside transport protein and the glucose-specific enzyme III (enzyme IIIGlc), a component of glucose transport and a key element in regulation of catabolite repression. These observations indicate that enzyme IIIGlc may, in conjunction with enzyme IIBgl, modulate the transport of beta-glucosides and the phosphorylation of the antiterminator protein. In the absence of both sugars, when the catabolite-controlled promoter of the operon is derepressed, enzyme IIIGlc may mediate tight repression of antitermination.

Bacterial Proteins↗
PubMed1970

Catabolite-insensitive revertants of lac promoter mutants.

The maximum rate of expression of the lac operon is severely reduced in lac promoter mutants. Revertants of these mutations which produce higher levels of enzyme were isolated. Some of these revertants had lost sensitivity to catabolite repression and transient repression. The mutations responsible for these losses took place at sites very close to the original promoter mutations. From these results we conclude that the promoter itself is the target site for both catabolite and transient repression of the lac operon.

Chromosome Mapping↗
PubMed1979

Cis-dominant regulatory mutations affecting the expression of GABA permease in Aspergillus nidulans.

In Aspergillus nidulans expression of the gabA gene, the probable structural gene for the gamma-amino-n-butyrate (GABA) permease, is controlled by induction, via the intA gene, ammonium repression, mediated by the areA gene, and probably carbon catabolite repression. Regulatory mutations, tightly linked to gabA, were selected by reverting an areAr-2 strain on GABA as nitrogen source. These mutations, gabI-1, gabI-2, and gabI-3 result in increased gabA expression and are cis-dominant in their effects on the gabA gene. Mapping data show that the regulatory mutations map on one side of all gabA- alleles tested.

Aspergillus nidulans↗
PubMed1994

Acidic-phospholipid deficiency represses the flagellar master operon through a novel regulatory region in Escherichia coli.

The Escherichia coli pgsA3 mutation, which causes acidic-phospholipid deficiency, was found to repress the flagellar master operon, as assessed by the beta-galactosidase activities of flhD-lacZ fusions. This explained the impairment of flagellar formation and motility by the mutation. A series of deletion analysis indicated that a 40-bp region, at the 5' end of the flhD locus examined, was responsible for the repression of a downstream transcription initiation that was catabolite-repression sensitive. This novel regulatory region was 200 bp upstream of the first possible translation initiation site.

Bacterial Proteins↗
PubMedDate not supplied

[Repression of the enzyme inducible syntheses in Escherichia coli K12 mutant with a deleted ptsH gene].

The genome of lambda phage with thermosensitive repressor was integrated into the pts region of the E. coli chromosome. Such a lysogenic culture behaves as a pts mutant at 30 degrees. Heating of cells of this strain leads to the induction of lambda prophage and formation of deletions in the pts region. A mutant with a deletion covering ptsH gene was isolated after prophage induction. The deletion nature of pts mutation was confirmed in genetic and biochemical experiments. It was shown that the deletion is small and does not involve ptsI and lig genes. The isolated deltaptsH mutant possesses all characteristics of pts mutants: pleiotropic impairment of transport and utilization of a number of carbohydrates, repression of the enzyme inducible synthesis and resistance to catabolite repression with glucose. These data (together with earlier ones) allow us to conclude that the phosphorylated form of HPr is involved (in direct of indirect manner/ in activation of DNA transcription.

Chromosomes, Bacterial↗
PubMed1979

Aminoglycosides, genes and regulation.

A major role has been played by aminoglycoside research in the development of fermentation science especially involving genetics and regulation. The first report of the use of an antibiotic to select high producers of that antibiotic was done with the streptomycin producer. Mutational biosynthesis of new antibiotics originated with studies on the neomycin producer. The first demonstration of the presence of genes coding for antibiotic inactivation in antibiotic producers was made with Streptomyces griseus, the producer of streptomycin. Induction of an enzyme involved in secondary metabolism was found first with mannosidostreptomycinase. The first example of a nonprecursor molecule which could induce an entire antibiotic biosynthetic pathway was A-Factor involved in streptomycin production. Glucose repression and amino acid repression of mannosidostreptomycinase were the first examples of carbon catabolite repression and nitrogen metabolite repression respectively of an enzyme involved in secondary metabolism. Data supporting the occurrence of nitrogen metabolite regulation of antibiotic biosynthesis were first gathered in the early days of development of the streptomycin fermentation when it was found that the slowly used soybean meal and proline were the best nitrogen sources for antibiotic production. Aminoglycoside research also provided the first explanation of a mechanism of phosphate control of antibiotic biosynthesis. The first indication that antibiotic formation is not obligatory for spore formation was provided by data on streptomycin production.

Aminoglycosides↗
PubMed1978

Analysis of the regulatory mechanisms controlling the synthesis of the hexitol transport systems in Escherichia coli K12.

The synthesis of the transport systems (enzymeII-complexes) coded for in the mtl and in the gut (srl) operon was found to be induced by unphosphorylated D-mannitol and D-glucitol respectively. Induction from the outside however is only possible if these polyols are taken up into the cells. Induction of the D-mannitol system is immediate, resistant against catabolite repression, relatively insensitive towards transient repression and starts from a high uninduced level (5--30%). By contrast, the induction of the D-glucitol system starts at a low basal level (0.5--2.5%), does show a pronounced lag from 25 to 90 min, and is hypersensitive towards catabolite and transient repression. These differences apparently reflect primarely differences in the corresponding operator-promotor genes mtl (P,O) and gut (P,O) as well as differences in the uptake of the first, inducing hexitol molecules. For each operon additional regulatory genes exist, called mtlR and gutR respectively, in which transrecessive, temperature sensitive mutations leading to a constitutive expression of the corresponding operon can be found. The influence of these regulatory mechanisms in diauxie experiments and their importance for the differentiation of the three operons during evolution from apparently one common ancestor operon will be discussed.

Biological Transport↗
PubMed1977

Repression of inducible enzyme synthesis in a mutant of Escherichia coli K 12 deleted for the ptsH gene.

The genome of lambda phage with thermosensitive repressor was inserted into the pts region of the Escherichia coli chromosome. This lysogenic culture possessed the PTS1 phenotype at 30 degrees C. A mutant strain with a deletion covering the ptsH gene was isolated after a prophage curing procedure. The deletion nature of the pts mutation was confirmed in genetical and biochemical experiments. The deletion covered a small fragment of the bacterial genome not extending in the ptsI and lig genes. The isolated deltaptsH mutant possessed all characteristics of known pts mutants: pleiotropical disturbances of transport and utilization of a number of carbohydrates, repression of the enzyme inducible synthesis, and resistance to glucose catabolite repression. From these and other data we can conclude that the phosphorylated form of the heat-stable protein HPr is involved (directly or indirectly) in activation of the DNA transcription process.

Bacterial Proteins↗
PubMed1978

Effect of environmental conditions on the production of two extracellular proteolytic enzymes by Vibrio SA1.

The production of two extracellular proteases, an endopeptidase and an aminopeptidase, by the marine bacterium Vibrio SA1 was studied in batch cultures. The production of the proteases was induced during growth of the organism in peptone media and by several amino acids during growth in minimal media. It was repressed by easily metabolisable carbon compounds such as glucose, lactate and succinate during growth in peptone media. During growth in a lactate basal medium, phenylalanine was one of the best inducers and this amino acid was therefore used in further experiments. That lactate did not repress the synthesis of the proteases during growth in the lactate basal medium supplement with 2mM phenylalanine as an inducer, appeared to be a consequence of the low iron content of this medium. Growth curves of Vibrio SA1 on such media showed a period of linear growth during which protease production was observed. When the iron concentration was made sufficiently high to prevent linear growth, the synthesis of the proteases remained repressed. Apparently by imposing an iron limitation on the organism, catabolite repression by lactate was relieved. Similarly, when growth was limited by very low values of the dissolved oxygen tension in the medium, a high rate of protease synthesis was found which was immediately repressed when the oxygen limitation was released. The results indicate that the growth rate and/or a factor associated with the energy metabolism play a role in the regulation of the synthesis of the enzymes.

Amino Acids↗
PubMed2006

Effect of Vitreoscilla hemoglobin on production of a chemotherapeutic enzyme, L-asparaginase, by Pseudomonas aeruginosa.

The production of L-asparaginase, an enzyme widely used in cancer chemotherapy, is mainly regulated by carbon catabolite repression and oxygen. This study was carried out to understand how different carbon sources and Vitreoscilla hemoglobin (VHb) affect the production of this enzyme in Pseudomonas aeruginosa and its VHb-expressing recombinant strain (PaJC). Both strains grown with various carbon sources showed a distinct profile of the enzyme activity. Compared to no carbohydrate supplemented medium, glucose caused a slight repression of L-asparaginase in P. aeruginosa, while it stimulated it in the PaJC strain. Glucose, regarded as one of the inhibitory sugars for the production L-asparaginase by other bacteria, was determined to be the favorite carbon source compared to lactose, glycerol and mannitol. Furthermore, contrary to common knowledge of oxygen repression of L-asparaginase in other bacteria, oxygen uptake provided by VHb was determined to even stimulate the L-asparaginase synthesis by P. aeruginosa. This study, for the first time, shows that in P. aeruginosa utilizing a recombinant oxygen uptake system, VHb, L-asparaginase synthesis is stimulated by glucose and other carbohydrate sources compared to the host strain. It is concluded that carbon catabolite and oxygen repression of L-asparaginase in fermentative bacteria is not the case for a respiratory non-fermentative bacterium like P. aeruginosa.

Antineoplastic Agents↗