Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Enzyme Repression”

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.

At least 1,405 records · Page 78Linked to original sources
PubMed1987

Constitutive expression of the yeast HEM1 gene is actually a composite of activation and repression.

We show that HEM1 (encoding 5-aminolevulinate synthase) expression, while constitutive under all steady-state growth conditions tested, is activated by the HAP2-HAP3 global activation system that controls expression of apocytochromes. This finding creates a paradox because apocytochrome activation by HAP2-HAP3 is highly regulated, subject to induction by heme, and subject to further derepression by a shift from glucose medium to one containing a nonfermentable carbon source. We clarify this issue by showing that HEM1 is subject to two additional layers of control that mask regulatory changes. First is a second activation system acting at a site close to the HAP2-HAP3 target sequence that keeps HEM1 turned on under conditions of heme deficiency. Second is a regulated negative control site downstream of the upstream activation site that counteracts derepression in medium containing a nonfermentable carbon source. Thus, transcription of the constitutive gene is actually a composite of opposing regulatory sites. This complex regulatory arrangement may exist to allow HEM1 to be coordinated transiently with apocytochromes for transition to respiratory growth. Conversely, it may reflect the alteration of HEM1 from a regulated to a constitutive gene over evolution.

5-Aminolevulinate Synthetase↗
PubMedDate not supplied

Role of an upstream regulatory element in leucine repression of the Saccharomyces cerevisiae leu2 gene.

The expression of a number of eukaryotic genes has been shown to involve at least two sequences located upstream of the actual transcription unit: one of these sequences, centred on a widely conserved TATAAT sequence, is thought to be involved in determining the precise site of initiation of transcription; the other has a gene-specific sequence, can function at a variable distance upstream of the initiation site, and is involved in the regulation of transcription. By constructing beta-galactosidase gene fusions, to facilitate measuring gene expression in vivo, we have now defined a cis-acting regulatory element of the Saccharomyces cerevisiae leu2 gene. This element is located within a 280 base pair (bp) fragment which occurs 125 bp upstream of the leu2 translation initiation codon and which contains a short G + C-rich palindromic sequence. A fragment of the Escherichia coli transposable element Tn9 which contains a similar palindromic sequence can functionally replace the natural leu2 regulatory element. Our results are contrary to previous speculations that the leu2 gene is regulated by an attenuation mechanism.

3-Isopropylmalate Dehydrogenase↗
PubMed1998

Identification of a novel transcriptional silencer in the protein-coding region of the human CYP2C9 gene.

A novel regulatory element (27 bp) which confers transcriptional repression was identified within the protein-coding region immediately after the translation start codon in the human cytochrome P450 (CYP) 2C9 gene. Deletion of this element increased transcriptional activity in HepG2 cells by transient transfection assay. Nuclear protein extracts from HepG2 cells and human liver were found in electrophoretic mobility shift assays to bind specifically to the 27 bp element. A putative binding protein was partially purified by DNA-affinity chromatography and was determined by Southwestern blotting to have a molecular weight of approx. 100 kDa. Studies with mutated competitor oligonucleotides established that binding of the nuclear protein to the 27 bp cis-element was dependent upon two 6 bp direct repeats (5'-CTTGTG-3') that were separated by three bases. It is possible that this novel cis-acting element may be involved in the negative regulation of CYP2C9.

Aryl Hydrocarbon Hydroxylases↗
PubMed1988

Cloning and characterization of the CYC8 gene mediating glucose repression in yeast.

Mutations in the CYC8 ( = SSN6) gene of Saccharomyces cerevisiae alleviate glucose repression of many glucose-repressible genes. The gene was isolated by screening for complementation of a cyc8 effect on colony morphology. Subclones containing a 5.3-kb SalI-XbaI fragment provided complete complementation. The gene was further localized to 3.5 kb by mapping of the CYC8 mRNA and insertional mutagenesis. Insertion and deletion mutations are viable and produce the same array of phenotypes as point mutations. CYC8 disruptions also had effects on the mating ability and morphology of MAT alpha cells similar to that of tup1 mutations. The nucleotide sequence of a 4866-bp fragment, including CYC8, was determined. One long open reading frame of 966 amino acid predicts a protein of molecular weight 10,7215. The predicted protein is extremely glutamine-rich, with blocks of 16 and 31 glutamines in tandem at the N and C regions, respectively. The CYC8 gene product lacks consensus sequences for DNA-binding domains, suggesting that its function may be different from classical repressor proteins.

Amino Acid Sequence↗
PubMed1979

Uptake and catabolism of D-xylose in Salmonella typhimurium LT2.

Salmonella typhimurium LT2 grows on D-xylose as sole carbon source with a generation time of 105 to 110 min. The following activities are induced at the indicated time after the addition of the inducer, D-xylose: D-xylulokinase (5 min), D-xylose isomerase (7 to 8 min), and D-xylose transport (10 min). All other pentoses and pentitols tested failed to induce isomerase or kinase. Synthesis of D-xylose isomerase was subject to catabolite repression, which was reversed by the addition of cyclic adenosine monophosphate. Most of the radioactive counts from D-[14C]xylose were initially accumulated in the cell in the form of D-xylose or D-xylulose. D-Xylose uptake in a mutant which was deficient in D-xylose isomerase was equal to that of the wild type. The apparent Km for D-xylose uptake was 0.41 mM. Some L-arabinose was accumulated in D-xylose-induced cells, and some D-xylose was accumulated in L-arabinose-induced cells. D-Xylitol and L-arabinose competed against C-xylose uptake, but D-arabinose, D-lyxose, and L-lyxose did not. Osmotic shock reduced the uptake of D-xylose by about 50%; by equilibrium dialysis, a D-xylose-binding protein was detected in the supernatant fluid after spheroplasts were formed from D-xylose-induced cells.

Biological Transport, Active↗
PubMed2006

Intracellular HIV-1 Tat protein represses constitutive LMP2 transcription increasing proteasome activity by interfering with the binding of IRF-1 to STAT1.

The Tat protein is the transcriptional activator of HIV-1 gene expression, which is not only essential for viral replication, but also important in the complex HIV-induced pathogenesis of AIDS, as both an intracellular and an extracellular released protein. Accordingly, Tat is able to profoundly affect cellular gene expression, regulating several cellular functions, also in non-infected cells. We showed recently that Tat induces modification of immunoproteasomes in that it up-regulates LMP7 (low-molecular-mass polypeptide 7) and MECL1 (multicatalytic endopeptidase complex-like 1) subunits and down-modulates the LMP2 subunit, resulting in a change in the generation and presentation of epitopes in the context of MHC class I. In particular, Tat increases presentation of subdominant and cryptic epitopes. In the present study, we investigated the molecular mechanism responsible for the Tat-induced LMP2 down-regulation and show that intracellular Tat represses transcription of the LMP2 gene by competing with STAT1 (signal transducer and activator of transcription 1) for binding to IRF-1 (interferon-regulatory factor-1) on the overlapping ICS-2 (interferon consensus sequence-2)-GAS (gamma-interferon-activated sequence) present in the LMP2 promoter. This element is constitutively occupied in vivo by the unphosphorylated STAT1-IRF-1 complex, which is responsible for the basal transcription of the gene. Sequestration of IRF-1 by intracellular Tat impairs the formation of the complex resulting in lower LMP2 gene transcription and LMP2 protein expression, which is associated with increased proteolytic activity. On the other hand, extracellular Tat induces the expression of LMP2. These effects of Tat provide another effective mechanism by which HIV-1 affects antigen presentation in the context of the MHC class I complex and may have important implications in the use of Tat for vaccination strategies.

Cysteine Endopeptidases↗
PubMed1988

DNA transfection of a gene repressing aryl hydrocarbon hydroxylase induction.

High mol. wt genomic DNA from a genetically dominant aryl hydrocarbon hydroxylase (AHH)-deficient mutant cell line derived from the mouse hepatoma cell line Hepa-1 was used to transfect the parent cell line. AHH-deficient transfectants were recovered following single-step selection in medium containing the carcinogen benzo[a]pyrene. The transfectants arose at a frequency of 2 x 10(-7). This frequency was at least 4-fold greater than the frequency of spontaneous forward mutation in this cell line. In another set of experiments, dominant mutant DNA was co-transfected along with the selectable plasmid pSV2ecogpt into parental Hepa-1 cells. The frequency of co-transfection was determined to be 3 x 10(-8). This frequency was approximately 150 times greater than that expected on the basis of coincident but unrelated spontaneous mutation and plasmid uptake. Both types of transfectants were judged, following somatic cell hybridizations, to possess the dominant phenotype of the mutant cell line, demonstrating that a trans-acting dominant negative regulator of AHH was transferred in these experiments. DNA transfection should therefore provide a means for the molecular cloning of the gene that encodes the dominant regulator.

Animals↗
PubMed1989

Nucleotide sequence of pho-4+, encoding a phosphate-repressible phosphate permease of Neurospora crassa.

The nucleotide (nt) sequence of the Neurospora crassa pho-4+ gene, which encodes a phosphate-repressible phosphate permease, has been determined. The gene specifies a protein of 590 amino acids (aa) and contains two introns. Two RNA transcripts of 3.3 and 2.4 kb have been identified, and transcription start points (tsp) and termination sites and/or processing sites have been located. The 3.3-kb message is initiated about 890 nt upstream from the tsp for the 2.4-kb transcript. A hydropathy profile of the aa sequence suggests ten to twelve membrane-spanning helices with a large hydrophilic domain between the eighth and ninth helices. This model for the predicted secondary structure of the protein is very similar to models proposed for other sequenced integral membrane proteins from both prokaryotes and eukaryotes. Since very few permease-encoding genes of eukaryotes have been examined in molecular detail, it will be of interest to compare the sequence of pho-4+ with those encoding other anion transport proteins, as they become available.

Amino Acid Sequence↗
PubMed1985

Regulation of repressible acid phosphatase gene transcription in Saccharomyces cerevisiae.

We examined the genetic system responsible for transcriptional regulation of repressible acid phosphatase (APase; orthophosphoric-monoester phosphohydrolase [acid optimum, EC 3.1.3.2]) in Saccharomyces cerevisiae at the molecular level by analysis of previously isolated and genetically well-defined regulatory gene mutants known to affect APase expression. These mutants identify numerous positive- (PHO4, PHO2, PHO81) and negative-acting (PHO80, PHO85) regulatory loci dispersed throughout the yeast genome. We showed that the interplay of these positive and negative regulatory genes occurs before or during APase gene transcription and that their functions are all indispensible for normal regulation of mRNA synthesis. Biochemical evidence suggests that the regulatory gene products they encode are expressed constitutively. More detailed investigation of APase synthesis is a conditional PHO80(Ts) mutant indicated that neither PHO4 nor any other protein factor necessary for APase mRNA synthesis is transcriptionally regulated by PHO80. Moreover, in the absence of PHO80, the corepressor, presumed to be a metabolite of Pi, did not inhibit their function in the transcriptional activation of APase.

Acid Phosphatase↗
PubMed1986

Suppressors of SNF2 mutations restore invertase derepression and cause temperature-sensitive lethality in yeast.

Mutations in the SNF2 gene of Saccharomyces cerevisiae prevent derepression of the SUC2 (invertase) gene, and other glucose-repressible genes, in response to glucose deprivation. We have isolated 25 partial phenotypic revertants of a snf2 mutant that are able to derepress secreted invertase. These revertants all carried suppressor mutations at a single locus, designated SSN20 (suppressor of snf2). Alleles with dominant, partially dominant and recessive suppressor phenotypes were recovered, but all were only partial suppressors of snf2, reversing the defect in invertase synthesis but not other defects. All alleles also caused recessive, temperature-sensitive lethality and a recessive defect in galactose utilization, regardless of the SNF2 genotype. No significant effect on SUC2 expression was detected in a wild-type (SNF2) genetic background. The ssn20 mutations also suppressed the defects in invertase derepression caused by snf5 and snf6 mutations, and selection for invertase-producing revertants of snf5 mutants yielded only additional ssn20 alleles. These findings suggest that the roles of the SNF2, SNF5 and SNF6 genes in regulation of SUC2 are functionally related and that SSN20 plays a role in expression of a variety of yeast genes.

Enzyme Repression↗
PubMed1998

Molecular analysis of the interaction between the Bacillus subtilis trehalose repressor TreR and the tre operator.

The trehalose operon of Bacillus subtilis is subject to regulation by induction, mediated by the repressor TreR, and by carbon catabolite repression (CCR). For in vitro investigations, TreR from B. subtilis was overproduced and purified. Its molecular mass, as estimated by SDS-PAGE, is 27 kDa. Size fractionation under native conditions yielded a size estimate of 56 kDa, indicating that TreR exists as a dimer in its native state. Analysis of its interaction with various DNA fragments shows that TreR is able to recognize two tre operators with different efficiencies, and indicates cooperative binding. Previous results have suggested that CCR of the tre operon occurs by a mechanism in which the specific regulator, TreR, may be involved independently of the central component, CcpA. The data presented here indicate that the TreR-tre operator interaction is influenced by several effectors. Thus, the presence of trehalose-6-phosphate, as well as glucose-1-phosphate and sodium chloride, inhibits tre operator binding. Glucose-6-phosphate can act as an anti-inducer, which might reflect its additional role in CCR exerted by glucose.

Bacillus subtilis↗
PubMed1996

Chromatin remodeling during Saccharomyces cerevisiae ADH2 gene activation.

We have analyzed at both low and high resolution the distribution of nucleosomes over the Saccharomyces cerevisiae ADH2 promoter region in its chromosomal location, both under repressing (high-glucose) conditions and during derepression. Enzymatic treatments (micrococcal nuclease and restriction endonucleases) were used to probe the in vivo chromatin structure during ADH2 gene activation. Under glucose-repressed conditions, the ADH2 promoter was bound by a precise array of nucleosomes, the principal ones positioned at the RNA initiation sites (nucleosome +1), at the TATA box (nucleosome -1), and upstream of the ADR1-binding site (UAS1) (nucleosome -2). The UAS1 sequence and the adjacent UAS2 sequence constituted a nucleosome-free region. Nucleosomes -1 and +1 were destabilized soon after depletion of glucose and had become so before the appearance of ADH2 mRNA. When the transcription rate was high, nucleosomes -2 and +2 also underwent rearrangement. When spheroplasts were prepared from cells grown in minimal medium, detection of this chromatin remodeling required the addition of a small amount of glucose. Cells lacking the ADR1 protein did not display any of these chromatin modifications upon glucose depletion. Since the UAS1 sequence to which Adr1p binds is located immediately upstream of nucleosome -1, Adr1p is presumably required for destabilization of this nucleosome and for aiding the TATA-box accessibility to the transcription machinery.

Alcohol Dehydrogenase↗
PubMed2005

Protein kinase C activates human lipocalin-type prostaglandin D synthase gene expression through de-repression of notch-HES signaling and enhancement of AP-2 beta function in brain-derived TE671 cells.

Here we investigated the regulatory mechanism of lipocalin-type prostaglandin D synthase (L-PGDS) gene expression in human TE671 (medulloblastoma of cerebellum) cells. Reporter analysis of the promoter region from -730 to +75 of the human L-PGDS gene demonstrated that deletion or mutation of the N-box at -337 increased the promoter activity 220-300%. The N-box was bound by Hes-1, a mammalian homologue of Drosophila Hairy and enhancer of split, as examined by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Functional expression of the Notch intracellular domain significantly increased Hes-1 expression and decreased L-PGDS expression level in TE671 cells. Moreover, knock-down of Hes-1 mRNA by RNA interference significantly enhanced the L-PGDS mRNA level, indicating that the L-PGDS gene expression is repressed by the Notch-Hes signaling. When the AP-2 element at -98 of the promoter region was deleted or mutated, the promoter activity was drastically decreased to approximately 10% of normal. The AP-2 element was bound by AP-2beta dominantly expressed in TE671 cells, according to the results of electrophoretic mobility shift assay and chromatin immunoprecipitation assay. L-PGDS expression was induced by 12-O-tetradecanoylphorbol-13-acetate in TE671 cells, and this induction was inhibited by a protein kinase C inhibitor. Stimulation of TE671 cells with 12-O-tetradecanoylphorbol-13-acetate or transfection with protein kinase Calpha expression vector induced phosphorylation of Hes-1, inhibition of DNA binding of Hes-1 to the N-box, and activation of the AP-2beta function to up-regulate L-PGDS gene expression. These results reveal a novel transcriptional regulatory mechanism responsible for the high level expression of the human L-PGDS gene in TE671 cells.

Basic Helix-Loop-Helix Proteins↗
PubMed1986

Constitutive RNA synthesis for the yeast activator ADR1 and identification of the ADR1-5c mutation: implications in posttranslational control of ADR1.

The regulation of mRNA production for the yeast positive activator ADR1, a gene required for the expression of the glucose-repressible alcohol dehydrogenase (ADH II), was studied. ADR1 mRNA levels did not vary when yeasts were switched from glucose- to ethanol-containing medium, while ADH II expression increased 100-fold. The mRNA for the ADR1-5c allele, which augments ADH II expression 60-fold during glucose repression, was not present in greater abundance than ADR1 mRNA. Additionally, the ccr1-1 allele, which blocks ADH2 mRNA formation and partially suppresses the ADR1-5c phenotype, did not alter the levels of ADR1 mRNA. These results indicate that ADR1 is not transcriptionally controlled. To determine the character of the ADR1-5c mutation, the region containing the mutation was identified and sequenced. At base pair +683 a G-to-A transition was detected in the ADR1 coding sequence which would result in the substitution of a lysine residue for an arginine at amino acid 228. The location of the ADR1-5c mutation in the interior of the ADR1 coding sequences suggests that it enhances the activity of an extant but inactive ADR1 protein rather than increases the abundance of ADR1 by altered translation of its mRNA. The ADR1-5c mutation occurs in a region of the polypeptide corresponding to a cyclic AMP-dependent protein kinase phosphorylation recognition sequence. The potential role of reversible phosphorylation in the posttranslational regulation of ADR1 is discussed.

Alcohol Dehydrogenase↗
PubMed1975

Regulation of nitrogenase synthesis in intact cells of Rhodospirillum rubrum: inactivation of nitrogen fixation by ammonia, L-glutamine and L-asparagine.

The synthesis of nitrogenase by intact cells of Rhodospirillum rubrum was repressed in N-free media supplemented with L-glutamine or L-asparagine, but was unaffected by the presence of L-glutamate, L-aspartate or L-histidine. Specific activities attained by cultures in supplemented media maintained under Ar-CO2 were 2 to 3 times higher than those in N-free medium under N2-CO2. A loss in total activity occurred both in cultures growing with N2 after maximum activity had been reached, and in cultures maintained under Ar when the gas phase was changed to N2. There was a rapid loss in nitrogen-fixing activity when low concentrations of NH4+, L-glutamine or L-asparagine were added to cultures with high activities, but this could be recovered in the absence of demonstrable protein synthesis. During growth, the degree of inactivation brought about by 0-5 mM-inactivator increased to 80 to 90%, and NH4+ excreted into the medium reached a maximum concentration towards the end of exponential growth.

Acetylene↗
PubMed1996

Ciprofibrate represses alpha 2u-globulin expression in liver and inhibits d-limonene nephrotoxicity.

Peroxisome proliferators are a class of compounds which induce hepatomegaly and peroxisome proliferation in liver parenchymal cells. One of the earliest known effects of peroxisome proliferators is the rapid transcriptional activation of the genes responsible for the peroxisomal beta-oxidation system in liver. Long term administration of these chemicals to rats and mice results in the development of hepatocellular carcinomas. Here we report that mRNA for alpha 2u-globulin, a rodent male specific protein, is markedly reduced or undetectable by Northern blot analysis of total RNA in the livers of rats treated with ciprofibrate. This was further confirmed by immunoblot analysis using antibodies against alpha 2u-globulin. Nevertheless, immunohistochemical staining and in situ hybridization showed respectively the presence of a few cells that contained alpha 2u-globulin protein and its mRNA. The alpha 2u-globulin mRNA reappeared in the liver 2 weeks following the cessation of ciprofibrate treatment. Feeding of ciprofibrate for two weeks followed by simultaneous feeding of ciprofibrate and a nephrotoxic chemical d-limonene for 5 weeks revealed that ciprofibrate prevented the renal accumulation of alpha 2u-globulin and the nephrotoxicity associated with the binding of d-limonene with alpha 2u-globulin.

Alpha-Globulins↗
PubMed1992

Glucose repression of the yeast ADH2 gene occurs through multiple mechanisms, including control of the protein synthesis of its transcriptional activator, ADR1.

The rate of ADH2 transcription increases dramatically when Saccharomyces cerevisiae cells are shifted from glucose to ethanol growth conditions. Since ADH2 expression under glucose growth conditions is strictly dependent on the dosage of the transcriptional activator ADR1, we investigated the possibility that regulation of the rate of ADR1 protein synthesis plays a role in controlling ADR1 activation of ADH2 transcription. We found that the rate of ADR1 protein synthesis increased 10- to 16-fold within 40 to 60 min after glucose depletion, coterminous with initiation of ADH2 transcription. Changes in ADR1 mRNA levels contributed only a twofold effect on ADR1 protein synthetic differences. The 510-nt untranslated ADR1 mRNA leader sequence was found to have no involvement in regulating the rate of ADR1 protein synthesis. In contrast, sequences internal to ADR1 coding region were determined to be necessary for controlling ADR1 translation. The ADR1c mutations which enhance ADR1 activity under glucose growth conditions did not affect ADR1 protein translation. ADR1 was also shown to be multiply phosphorylated in vivo under both ethanol and glucose growth conditions. Our results indicate that derepression of ADH2 occurs through multiple mechanisms involving the ADR1 regulatory protein.

Alcohol Dehydrogenase↗
PubMed1980

Repression of nitrate reductase activity and loss of antigenically detectable protein in Neurospora crassa.

Experiments were performed to determine whether conditions which cause the rapid loss of nitrate reductase activity in Neurospora crassa mycelia were accompanied by the loss of antigenically detectable nitrate reductase protein. When mycelia with nitrate reductase activity were transferred to ammonia media, there was a rapid loss in the reduced nicotinamide adenine dinucleotide-nitrate reductase activity plus the parallel loss of the reduced nicotinamide adenine dinucleotide-diaphorase and the reduced methyl viologen-nitrate reductase activities associated with the nitrate reductase. In addition, there was the loss of cross-reacting material to anti-nitrate reductase antisera that was concomitant with the loss of nitrate reductase activity. When mycelia were exposed to either ammonia plus cycloheximide, nitrate plus cycloheximide, or nitrogen-free media, or to media which lacked an assimilable carbon source, the amount of cross-reacting material declined in concert with the nitrate reductase activity. The mutant nit-6, which lacks nitrite reductase activity, was exposed to ammonia or nitrate plus cycloheximide media. The nitrate reductase and the amount of cross-reacting material declined together as in the wild-type mycelia. We conclude that the loss of nitrate reductase activity was accompanied by the specific loss of this protein and that no pool of inactivated nitrate reductase molecules existed.

Ammonia↗