SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
We report the presence of a single L-asparagine aminohydrolase activity (EC 3.5.1.1) in extracts of Bacillus licheniformis A5. The synthesis of the enzyme was apparently under nitrogen catabolite repression control.
Transcription of the vacuolar aminopeptidase yscI (APE1) gene in Saccharomyces cerevisiae has previously been suggested to require the participation of a cis upstream activation sequence (UAS) involved in carbon catabolite repression that responds to glucose. To determine the structure of the APE1 UAS element, we used the 18-bp sequence 5'-ATGAATTAGTCAGCTTCT-3' as the DNA-binding site. Using gel mobility shift assays, we have identified a 78 kDa protein from yeast that binds specifically to both single and double-stranded forms of the UAS DNA-binding site. We have also identified a 48 kDa heterodimer from yeast that binds specifically to the single-stranded form of the UAS and whose DNA binding activity is remarkably heat stable. Even though the APE1 UAS contains a consensus sequence for the binding of the yeast activator protein yAP1, the two DNA-protein complexes could still be detected in a strain bearing a deletion in the YAP1 gene.
Aspergillus nidulans synthesizes penicillins as secondary metabolites when grown under certain culture conditions. Broths containing carbon (C) sources that give rise to carbon catabolite repression (CCR) support a much lower antibiotic yield than broths with non-repressing C sources. Steady-state levels of the isopenicillin N synthetase (IPNS) gene transcript are considerably reduced in mycelia grown with repressing C sources and are depressed in mycelia grown with sugars which do not cause CCR, indicating that penicillin biosynthesis is regulated by CCR through transcriptional control of structural genes. CCR is sufficient to explain the temporal window of expression of the IPNS gene during the growth cycle since (i) the transcript becomes derepressed as soon as the concentration of a repressing C source drops to non-repressing levels and (ii) derepressing C sources sustain derepressed IPNS transcription at all tested moments of the growth cycle. Several tested hypofunctional mutations in creA (the negatively acting regulatory gene which mediates CCR in A. nidulans) do not cause full derepression of IPNS transcript in the presence of a repressing C source. The slight degree of IPNS derepression caused by some creAd (derepressed) alleles parallels the strength of the mutation (as determined by the morphological effect they elicit).
HPr kinase/phosphorylase (HPrK/P), a central metabolic regulator in many Gram-positive bacteria, reversibly phosphorylates HPr and Crh, thus controlling their activities as effectors of CcpA predominantly in carbon catabolite repression (CCR). We have placed the constitutively expressed hprK in its native chromosomal locus under anhydrotetracycline-dependent transcriptional control to establish the correlation between HPrK/P amounts and the efficiency of CCR in Bacillus subtilis. This resulted in about eightfold repression of HPrK/P expression but had no effect on CCR as monitored by xynP'-lacZ reporter gene expression and by analysis of RocG protein amounts. These results suggest that very small amounts of HPrK/P are sufficient for complete CCR and that control of HPrK/P activity depends only on the presence of effectors and not on the abundance of the enzyme.
Vibrio alginolyticus, a halophilic marine bacterium, produced an extracellular amylase with a molecular mass of approximately 56,000, and the amylase appeared to be subject to catabolite repression mediated by cAMP. The production of amylase at pH 6.5, at which the respiratory chain-linked H+ pump functions, was inhibited about 75% at 24 hours following the addition of 2 microM carbonyl cyanide m-chlorophenylhydrazone (CCCP), while the production at pH 8.5, at which the respiratory chain-linked Na+ pump functions, was only slightly inhibited by the addition of 2 microM CCCP. In contrast, the production of amylase in a mutant bacterium defective in the Na+ pump was almost completely inhibited even at pH 8.5 as well as pH 6.5 by the addition of 2 microM CCCP.
The growth of Pullularia pullulans on L-rhamnose (6-deoxy-L-mannose) as the sole carbon source induces the synthesis of L-rhamnose dehydrogenase, a nicotinamide adenine dinucleotide-dependent enzyme that catalyzes the oxidation of the deoxy sugar to L-rhamnonolactone. The enzyme induction is inhibited by cycloheximide, suggesting de novo synthesis. The presence of d-glucose (0.2%) or D-galactose (0.2%) simultaneously with the inducer in the induction medium produced 50% repression of dehydrogenase synthesis, but no effect was detected with D-fructose and D-mannose at the same concentration. High levels of D-glucose (2%), under maximal catabolite repression conditions, produced a complete inhibition of enzyme synthesis.
The synthesis of the C1-type isocitrate lyase found during growth of Pseudomonas MA on methylamine was investigated. It was shown that this enzyme is subject to catabolite repression by preferred carbon sources, e.g., succinate, and by ammonia. The carbon repression can be overcome by cyclic AMP, which was shown to be acting at the transcriptional level. Repression by ammonia is overcome during growth with methylamine as sole nitrogen, but not carbon, source. Uptake experiments showed that the uptake of methylamine from the medium was prevented by ammonia in the presence, but not in the absence, of an alternative carbon source. Measurement of cyclic AMP levels in cells grown on methylamine and on succinate, glycerol, glucose and acetate as carbon sources (with ammonium chloride as nitrogen source) revealed that methylamine-grown cells have the lowest cyclic AMP level despite having the highest C1-type isocitrate lyase activity. Cells grown on acetate with methylamine as sole nitrogen source possess both C1-type and C2-type isocitrate lyase. The results indicate that the synthesis of C1-isocitrate lyase is under control by repression-derepression involving a specific inducer, cyclic AMP, and an effector whose action is related to the nitrogen supply of the cell.
The regulation of carbon utilization is of central importance in the gene expression pathways for both morphological development and antibiotic production in Streptomyces species. We report the identification and characterization of a mutation in Streptomyces coelicolor, ccrA1, that affects the expression of several catabolite-controlled promoters. ccrA1 mutants are altered in expression of galP1, the glucose-sensitive, galactose-dependent promoter of the galactose utilization operon; in expression of the glycerol utilization operon, which is glucose sensitive and glycerol dependent; and in expression of chi63, the glucose-sensitive chitin-dependent promoter of a gene involved in chitin utilization. ccrA1 has no effect on the expression of galP2, a promoter that directs constitutive transcription of the galE and galK genes. ccrA1 maps to a region of the S. coelicolor genome which distinguishes it from other mutations known to be involved in catabolite control. We suggest that ccrA1 identifies a gene whose product may be involved in the general regulation of carbon catabolite repression in this complex bacterium.
2-deoxyglucose (2-DOG), a non-metabolize analogue of glucose, is taken up by yeast using the same transporter(s) as glucose and is phosphorylated by hexokinases producing 2-deoxyglucose-6-P. We found that in DOGR yeasts, 2-DOG was not able to trigger glucose repression, even at concentrations of 0.5%. This result suggests that the specific 2-DOG-6P phosphatase, the enzyme responsible for the DOGR phenotype, may be involved in inhibiting the process of catabolite repression mediated by 2-DOG.
Saccharomyces cerevisiae responds to nitrogen availability in several ways. (i) The cell is able to distinguish good nitrogen sources from poor ones through a process designated nitrogen catabolite repression (NCR). Good and poor nitrogen sources do not demonstrably affect the cell cycle other than to influence the cell's doubling time. (ii) Nitrogen starvation promotes the initiation of sporulation and pseudohyphal growth. (iii) Nitrogen starvation strongly affects the cell cycle; nitrogen-starved cells arrest in G1. A specific allele of the SUP70/CDC65 tRNAGln gene (sup70-65) has been reported to be defective in nitrogen signaling associated with pseudohyphal formation, sporulation, and NCR. Our data confirm that pseudohyphal growth occurs gratuitously in sup70-65 mutants cultured in nitrogen-rich medium at 30 degrees C. However, we find neither any defect in NCR in the sup70-65 mutant nor any alteration in the control of YVH1 expression, which has been previously shown to be specifically induced by nitrogen starvation.
The "start" cell division control genes CDC36 and CDC28 have been reported to contain a certain sequence homology to tissue oncogenes (ets and some protein kinase encoding oncogenes respectively). Here we report that temperature sensitive mutations in these genes are suppressed in cytoplasmic "petite" mutants and catabolite repression resistant mutants.
Conversion of lignocellulose to lactic acid requires strains capable of fermenting sugar mixtures of glucose and xylose. Recombinant Escherichia coli strains were engineered to selectively produce L-lactic acid and then used to ferment sugar mixtures. Three of these strains were catabolite repression mutants (ptsG(-)) that have the ability to simultaneously ferment glucose and xylose. The best results were obtained for ptsG(-) strain FBR19. FBR19 cultures had a yield of 0.77 (g lactic acid/g added sugar) when used to ferment a 100 g/l total equal mixture of glucose and xylose. The strain also consumed 75% of the xylose. In comparison, the ptsG(+) strains had yields of 0.47-0.48 g/g and consumed 18-22% of the xylose. FBR19 was subsequently used to ferment a variety of glucose (0-40 g/l) and xylose (40 g/l) mixtures. The lactic acid yields ranged from 0.74 to 1.00 g/g. Further experiments were conducted to discover the mechanism leading to the poor yields for ptsG(+) strains. Xylose isomerase (XI) activity, a marker for induction of xylose metabolism, was monitored for FBR19 and a ptsG(+) control during fermentations of a sugar mixture. Crude protein extracts prepared from FBR19 had 10-12 times the specific XI activity of comparable samples from ptsG(+) strains. Therefore, higher expression of xylose metabolic genes in the ptsG(-) strain may be responsible for superior conversion of xylose to product compared to the ptsG(+) fermentations.
Galactose does not allow growth of pyruvate carboxylase mutants in media with ammonium as a nitrogen source, and inhibits growth of strains defective in phosphoglyceromutase in ethanol-glycerol mixtures. Starting with pyc1, pyc2, and gpm1 strains, we isolated mutants that eliminated those galactose effects. The mutations were recessive and were named dgr1-1 and dgr2-1. Strains bearing those mutations in an otherwise wild-type background grew slower than the wild type in rich galactose media, and their growth was dependent on respiration. Galactose repression of several enzymes was relieved in the mutants. Biochemical and genetic evidence showed that dgr1-1 was allelic with GAL2 and dgr2-1 with GAL4. The results indicate that the rate of galactose consumption is critical to cause catabolite repression.
Mutants able to utilize 5'-AMP or cyclic AMP as the adenine source were isolated from an ade6 ade10 double mutant by ethyl methane sulfonate mutagenesis. A single amp1 mutation, primarily selected on 5'-AMP medium, confers the phenotype for utilization of exogenous 5'-AMP as the adenine source. From the ade6 ade10 amp1 triple mutant, a mutant able to utilize cyclic AMP was isolated, and the mutant phenotype was proven to be due to the simultaneous occurrence of triple mutations designated as cam1, cam2, and cam3. The cam3 mutation, but not cam1 or cam2, also confers the phenotype for utilizing 5'-AMP, the same phenotype as the amp1 mutation. All of these mutations are recessive to the respective wild-type counterparts. Cells having the ade6 ade10 amp1 cam1 cam2 cam3 genotype showed significant ability to take up exogenous cyclic AMP, whereas no differences were observed in cyclic AMP phosphodiesterase activity in comparison with that of the original strains used in the mutant isolation. Since glucose severely repressed galactokinase synthesis in the constitutive GAL81 mutant having the ade6 ade10 amp1 cam1 cam2 cam3 genotype, irrespective of the presence or absence of cyclic AMP in the medium, it was suggested that cyclic AMP is not involved in the mechanism of catabolite repression in Saccharomyces cerevisiae. It does, however, have a stimulative effect on the galactokinase synthesis in the GAL81 mutant in the absence of glucose.
The past decade has witnessed an exiting unveiling of numerous molecular mechanisms that characterize signal transduction by protein-protein interaction. The recent findings encouraged an increasing effort to understand the sequential metabolism of different sugars available as energy sources at the same time. It seems probable that at least three principle mechanisms which act together or separately, mediate carbon catabolite repression (CCR) depending on the system which is under metabolic control: i) by the main signal transducing chain via the ATP-dependent HPr-kinase, HPr(Ser46-P) or alternatively Crh via the central component CcpA and its interaction with cre, ii) by signals sensed from the specific regulators directly or via phosphorylation by HPr, iii) by inducer exclusion based on the concurrence of the enzyme IIA(Glc) domain of the glucose permease, and other PTS-dependent permeases composed only of the B and C domains and lacking the enzyme IIA domain.
The nucleic acid and deduced amino-acid sequences of the pectate lyase gene (pelA) from Aspergillus nidulans are presented. The pelA gene contains two short introns, 68 and 49 bp in length, and encodes a peptide of 326 amino acids. Five transcriptional start sites are clustered between 65 and 79 bp upstream of the start codon as determined by primer extension. Comparison of the amino-acid sequences of pectate or pectin lyases from bacteria, fungi and plants revealed less than 30% overall identity. However, five regions within these enzymes, in particular domains associated with the active site, are highly conserved with amino-acid similarities greater than 50%. Phylogenetic analysis using the principle of parsimony (PAUP 3.1.1) showed that pelA is most closely related to pectate lyases from plants rather than pectin lyases from other fungi. Previously, pelA was shown to be induced by polygalacturonic acid and repressed in the presence of preferred carbon sources, such as glucose. Gel mobility shift analysis indicates that a PstI-SphI fragment from the pelA promoter binds to a fusion protein composed of the N-terminal part of CREA, a protein involved in carbon catabolite repression, and glutathione-S-transferase. This result suggests CREA may contribute to the regulation of pelA expression.
Yeasts with disruptions in the genes PYC1 and PYC2 encoding the isoenzymes of pyruvate carboxylase cannot grow in a glucose-ammonium medium (Stucka et al. (1991) Mol. Gen. Genet. 229, 307-315). We have isolated a dominant mutation, BPC1-1, that allows growth in this medium of yeasts with interrupted PYC1 and PYC2 genes. The BPC1-1 mutation abolishes catabolite repression of a series of genes and allows expression of the enzymes of the glyoxylate cycle during growth in glucose. A functional glyoxylate cycle is necessary for suppression as a disruption of gene ICL1 encoding isocitrate lyase abolished the phenotypic effect of BPC1-1 on growth in glucose-ammonium. Concurrent expression from constitutive promoters of genes ICL1 and MLS1 (encoding malate synthase) also suppressed the growth phenotype of pyc1 pyc2 mutants. The mutation BPC1-1 is either allelic or closely linked to the mutation DGT1-1.
BACKGROUND: Expression of the bgl operon of Escherichia coli, involved in the regulated uptake and utilization of aromatic beta-glucosides, is extremely sensitive to the presence of glucose in the growth medium. We have analysed the mechanism by which glucose exerts its inhibitory effect on bgl expression. RESULTS: Our studies show that initiation of transcription from the bgl promoter is only marginally sensitive to glucose. Instead, glucose exerts a more significant inhibition on the elongation of transcription beyond the rho-independent terminator present within the leader sequence. Transcriptional analyses using plasmids that carry mutations in bglG or within the terminator, suggest that the target for glucose-mediated repression is the anti-terminator protein, BglG. Introduction of multiple copies of bglG or the presence of mutations that inhibit its phosphorylation by Enzyme IIBgl (BglF), result in loss of glucose repression. Studies using crp, cya and crr strains show that both CRP-cAMP and the Enzyme IIAGlc (EIIAGlc) are involved in the regulation. Although transcription initiation is normal in a crp, cya double mutant, no detectable transcription is seen downstream of the terminator, which is restored by a mutation within the terminator. Transcription past the terminator is also partly restored by the addition of exogenous cAMP to glucose-grown cultures of a crp+ strain. Glucose repression is lost in the crr mutant strain. CONCLUSIONS: The results summarized above indicate that glucose repression in the bgl operon is mediated at the level of transcription anti-termination, and glucose affects the activity of BglG by altering its phosphorylation by BglF. The CRP-cAMP complex is also involved in this regulation. The results using the crr mutant suggest a negative role for EIIAGlc in the catabolite repression of the bgl genes.