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PubMed1995

Glucose kinase-dependent catabolite repression in Staphylococcus xylosus.

By transposon Tn917 mutagenesis, 16 mutants of Staphylococcus xylosus were isolated that showed higher levels of beta-galactosidase activity in the presence of glucose than the wild-type strain. The transposons were found to reside in three adjacent locations in the genome of S. xylosus. The nucleotide sequence of the chromosomal fragment affected by the Tn917 insertions yielded an open reading frame encoding a protein with a size of 328 amino acids with a high level of similarity to glucose kinase from Streptomyces coelicolor. Weaker similarity was also found to bacterial fructokinases and xylose repressors of gram-positive bacteria. The gene was designated glkA. Immediately downstream of glkA, two open reading frames were present whose deduced gene products showed no obvious similarity to known proteins. Measurements of catabolic enzyme activities in the mutant strains grown in the presence or absence of sugars established the pleiotropic nature of the mutations. Besides beta-galactosidase activity, which had been used to detect the mutants, six other tested enzymes were partially relieved from repression by glucose. Reduction of fructose-mediated catabolite repression was observed for some of the enzyme activities. Glucose transport and ATP-dependent phosphorylation of HPr, the phosphocarrier of the phosphoenolpyruvate:carbohydrate phosphotransferase system involved in catabolite repression in gram-positive bacteria, were not affected. The cloned glkA gene fully restored catabolite repression in the mutant strains in trans. Loss of GlkA function is thus responsible for the partial relief from catabolite repression. Glucose kinase activity in the mutants reached about 75% of the wild-type level, indicating the presence of another enzyme in S. xylosus. However, the cloned gene complemented an Escherichia coli strain in glucose kinase. Therefore, the glkA gene encodes a glucose kinase that participates in catabolite repression in S. xylosus.

Amino Acid Sequence↗

PubMed2001

O2R, a novel regulatory element mediating Rox1p-independent O(2) and unsaturated fatty acid repression of OLE1 in Saccharomyces cerevisiae.

Fatty acid desaturation catalyzed by fatty acid desaturases requires molecular oxygen (O(2)). Saccharomyces cerevisiae cells derepress expression of OLE1 encoding Delta9 fatty acid desaturase under hypoxic conditions to allow more-efficient use of limited O(2). It has been proposed that aerobic conditions lead to repression of OLE1 by well-established O(2)-responsive repressor Rox1p, since putative binding sequences for Rox1p are present in the promoter of OLE1. However, we revealed in this study that disruption of ROX1 unexpectedly did not affect the O(2) repression of OLE1, indicating that a Rox1p-independent novel mechanism operates for this repression. We identified by promoter deletion analysis the 50-bp O(2)-regulated (O2R) element in the OLE1 promoter approximately 360 bp upstream of the start codon. Site-directed mutagenesis of the O2R element showed that the putative binding motif (5'-GATAA-3') for the GATA family of transcriptional factors is important for O(2) repression. Anaerobic derepression of OLE1 transcription was repressed by unsaturated fatty acids (UFAs), and interestingly the O2R element was responsible for this UFA repression despite not being included within the fatty acid-regulated (FAR) element previously reported. The fact that such a short 50-bp O2R element responds to both O(2) and UFA signals implies that O(2) and UFA signals merge in the ultimate step of the pathways. We discuss the differential roles of FAR and O2R elements in the transcriptional regulation of OLE1.

Anaerobiosis↗

PubMed2002

Control of inducer accumulation plays a key role in succinate-mediated catabolite repression in Sinorhizobium meliloti.

The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti favors succinate and related dicarboxylic acids as carbon sources. As a preferred carbon source, succinate can exert catabolite repression upon genes needed for the utilization of many secondary carbon sources, including the alpha-galactosides raffinose and stachyose. We isolated lacR mutants in a genetic screen designed to find S. meliloti mutants that had abnormal succinate-mediated catabolite repression of the melA-agp genes, which are required for the utilization of raffinose and other alpha-galactosides. The loss of catabolite repression in lacR mutants was seen in cells grown in minimal medium containing succinate and raffinose and grown in succinate and lactose. For succinate and lactose, the loss of catabolite repression could be attributed to the constitutive expression of beta-galactoside utilization genes in lacR mutants. However, the inactivation of lacR did not cause the constitutive expression of alpha-galactoside utilization genes but caused the aberrant expression of these genes only when succinate was present. To explain the loss of diauxie in succinate and raffinose, we propose a model in which lacR mutants overproduce beta-galactoside transporters, thereby overwhelming the inducer exclusion mechanisms of succinate-mediated catabolite repression. Thus, some raffinose could be transported by the overproduced beta-galactoside transporters and cause the induction of alpha-galactoside utilization genes in the presence of both succinate and raffinose. This model is supported by the restoration of diauxie in a lacF lacR double mutant (lacF encodes a beta-galactoside transport protein) grown in medium containing succinate and raffinose. Biochemical support for the idea that succinate-mediated repression operates by preventing inducer accumulation also comes from uptake assays, which showed that cells grown in raffinose and exposed to succinate have a decreased rate of raffinose transport compared to control cells not exposed to succinate.

Bacterial Proteins↗

PubMed1966

Nature of the effector of catabolite repression of beta-galactosidase in Escherichia coli.

Loomis, William F., Jr. (Massachusetts Institute of Technology, Cambridge, Mass.), and Boris Magasanik. Nature of the effector of catabolite repression of beta-galactosidase in Escherichia coli. J. Bacteriol. 92:170-177. 1966.-Many carbon sources were found to give rise to catabolite repression of beta-galactosidase in a mutant strain of Escherichia coli lacking hexose phosphate isomerase activity. Compounds containing glucose or galactose cannot be formed from several of these carbon sources in this mutant strain, and, therefore, appear not to be required for catabolite repression of beta-galactosidase. Glucose was observed to elicit catabolite repression of beta-galactosidase in another mutant strain under conditions in which the formation of compounds of the citric acid cycle is inhibited. If catabolite repression of the lac operon is mediated by a single compound, it appears that the compound is related to the pentoses and trioses of intermediary metabolism. The repression of beta-galactosidase by galactose in galactokinase negative strains was shown to be independent of the gene, CR, which determines catabolite sensitivity of the lac operon, and to be dependent on a functional i gene.

Carbohydrates↗

PubMed1994

Transcriptional repression by Drosophila and mammalian Polycomb group proteins in transfected mammalian cells.

The Polycomb group (Pc-G) genes are essential for maintaining the proper spatially restricted expression pattern of the homeotic loci during Drosophila development. The Pc-G proteins appear to function at target loci to maintain a state of transcriptional repression. The murine oncogene bmi-1 has significant homology to the Pc-G gene Posterior sex combs (Psc) and a highly related gene, Suppressor two of zeste [Su(z)2]. We show here that the proteins encoded by bmi-1 and the Pc-G genes Polycomb (Pc) and Psc as well as Su(z)2 mediate repression in mammalian cells when targeted to a promoter by LexA in a cotransfection system. These fusion proteins repress activator function by as much as 30-fold, and the effect on different activation domains is distinct for each Pc-G protein. Repression is observed when the LexA fusion proteins are bound directly adjacent to activator binding sites and also when bound 1,700 bases from the promoter. These data demonstrate that the products of the Pc-G genes can significantly repress activator function on transiently introduced DNA. We suggest that this function contributes to the stable repression of targeted loci during development.

3T3 Cells↗

PubMed1994

A segment of mRNA encoding the leader peptide of the CPA1 gene confers repression by arginine on a heterologous yeast gene transcript.

The expression of the yeast gene CPA1, which encodes the small subunit of the arginine pathway carbamoylphosphate synthetase, is repressed by arginine at a translational level. CPA1 mRNA contains a 250-nucleotide-long leader which includes a 25-codon upstream open reading frame (uORF). Oligonucleotide site-directed mutagenesis of this uORF as well as sequencing of constitutive cis-dominant mutations has suggested that the leader peptide product of the CPA1 uORF is an essential negative element for repression of the CPA1 gene by arginine. In this work, a series of deletions affecting the regions 5' and 3' to the uORF in the leader sequence was constructed. The arginine-dependent repression of CPA1 was little affected in these constructions, indicating that these regions are not essential for the regulatory response. This conclusion was further supported by the finding that inserting the mRNA segment encoding the leader peptide sequence of CPA1 in the leader sequence of another gene, namely, GCN4, places this gene under arginine repression. Similarly, the behavior of fusions of the leader sequence of CPA1 with those of ARG4 or GAL10 confirmed that the regions of this leader located upstream and downstream from the uORF are dispensable for the regulation by arginine. Finally, a set of substitution mutations which modify the uORF nucleotide sequence while leaving unchanged the corresponding amino acid sequence was constructed. The mutations did not affect the repression of CPA1 by arginine. The data presented in this paper consequently agree with the conclusion that the leader peptide itself is the main element required for the translational repression of CPA1.

Amino Acid Sequence↗

PubMed1986

Human argininosuccinate synthetase minigenes are subject to arginine-mediated repression but not to trans induction.

The human argininosuccinate synthetase locus is subject to metabolite-mediated repression by arginine in some cultured cell lines. To gain insight into the mechanism underlying this regulation, chloramphenicol acetyltransferase (CAT) minigenes under the transcriptional control of the human argininosuccinate synthetase promoter were constructed and tested for regulation. When the minigenes were introduced into RPMI 2650 cells, a human cell line that shows sixfold regulation of the argininosuccinate synthetase gene, CAT expression was repressed three- to fivefold when arginine was present in the culture medium. A minigene containing only 149 base pairs of 5'-flanking sequence was expressed at similar levels and regulated to the same degree as one having approximately 3 kilobases of 5'-flanking sequence. Therefore, the cis-acting sequences required for the arginine-mediated repression are likely to be located within the region of the transcription initiation site. The arginine-mediated repression of the CAT minigenes was not observed in canavanine-resistant variants of RPMI 2650 cells, and therefore they showed the appropriate cell-type specificity. Cultured cells having 200-fold-increased levels of argininosuccinate synthetase can be selected by growth in medium containing the arginine analog canavanine. It was previously demonstrated that the increased expression of argininosuccinate synthetase in canavanine-resistant human lymphoblasts was due to a trans-acting mechanism. To gain further support for a trans-acting mechanism, we tested our CAT minigenes for the trans induction in canavanine-resistant variants of RPMI 2650 cells. Transfection of the CAT minigenes into RPMI 2650 cells and canavanine-resistant variants of this cell line yielded no difference in transient CAT expression. Furthermore, cloned canavanine-resistant variant cells having integrated copies of the CAT minigenes expressed CAT at similar levels as compared to the parental cell lines. Since these cell lines do exhibit arginine-mediated repression of CAT but not trans induction, these data indicate that the argine-mediated repression is a regulatory event that occurs independently of the trans induction.

Arginine↗

PubMed1979

[Induction and repression of the collagenase synthesis in Acinetobacter sp].

The synthesis of collagenase in Acinetobacter sp. was found to be inducible by denatured collagen and by its high molecular weight fragments. The presence in the inducer of part of the tertiary structure appear to be indispensable. On the other hand, an addition of Casamino acids, meat protein hydrolysate, or a mixture of amino acids with a similar composition to gelatin does not stimulate collagenase synthesis. Enzyme production was severely repressed in the early phase of growth by glucose, arabinose, and ribose, single amino acids, proline, hydroxyproline, alanine, glutamic acid or casein acid hydrolysate. A mechanism of repression similar to catabolite repression was involved in the phenomenon caused by carbohydrates. However, the fact that cyclic adenosine 3'5-monophosphate did not overcome the repression caused by amino acids or Casamino acids, in contrast to classical catabolite repression, suggests that these two forms of repression may be distinct.

Acinetobacter↗

PubMed2003

Associations between repression, general maladjustment, body weight, and body shape in older males: the Normative Aging Study.

We examined relationships between repression, general maladjustment, body mass index (BMI), and waist-to-hip ratio (WHR). The participants were 1,081 healthy older men from the Normative Aging Study. Repression and General Maladjustment Scales of the Minnesota Multiphasic Personality Inventory were composite measures of personality. Repression was associated with lower BMI and WHR, and maladjustment with higher BMI and WHR. However, associations between WHR and personality dimensions were no longer significant when controlling for BMI, but associations between BMI and personality dimensions remained significant when controlling for WHR. These effects were explained by differing relationships between WHR, repression, and maladjustment for normal weight, overweight, and obese individuals. Specifically, associations between repression, maladjustment, and body shape were significant for normal weight and overweight individuals, but not for obese individuals. Health behaviors including smoking did not mediate relationships between repression, maladjustment, and body shape, but might be considered in future studies as mechanisms underlying links between personality and body shape.

Adjustment Disorders↗

PubMed2002

The repressed and implicit knowledge.

The distinction between implicit (non-conscious) and explicit (conscious) knowledge made by cognitive scientists is applied to the psychoanalytic idea of repressed contents. The consequences of repression are suggested to have been caused by implicit representations. Repressed memories can also be treated in terms of explicit representations, which are prevented from becoming activated. Implicit knowledge cannot, however, be made conscious, and thus the idea of becoming conscious of the repressed desires and fears that have never been conscious is contradictory. This tension may be relieved by reconceptualising the idea of becoming conscious of the repressed. It is suggested that this could be seen as creating explicit knowledge about the effects of implicit representations. By applying the implicit/explicit knowledge distinction, psychoanalytic ideas concerning the repressed could be connected to current views in the domain of cognitive orientation.

Cognition↗

PubMed2001

Repressive adaptation in children with cancer: a replication and extension.

Prior research has shown a higher incidence of a repressive adaptive style in children with cancer. To explore whether repressive adaptation in this population is premorbid or reactive, adaptive style was assessed longitudinally in children with cancer at the time of diagnosis and at 6 months and 1 year after diagnosis. Comparison groups included healthy children and children with other serious but nonmalignant chronic illnesses. At diagnosis, children with cancer showed a higher incidence of a repressive adaptive style than healthy children, and the incidence of repressive adaptation remained stable over time. Children with other chronic illnesses also showed levels of repressive adaptive style comparable to the cancer group. These findings suggest a shift toward repressiveness in response to the diagnosis of cancer that is then maintained over time and necessitate further examination of the health consequences of adaptive style in this population.

Adaptation, Psychological↗

PubMed1986

Primal repression: clinical and theoretical aspects.

Primal repression, long an obscure and unusable concept, has been given a precise place in a recent re-working of the theory of repression (Cohen & Kinston, 1984); and this paper specifically examines its properties and presentation. Primal repression refers to an absence of psychic structure which can be made good in the process of emotional growth. It is a part of the mind where trauma persists; and it has a close connexion to the unrepressed unconscious. Direct emergence of primal repression is a threat to life and its activation is therefore risky. During psychoanalysis, primal repression is normally avoided by object-narcissism buttressed by neurotic defences, but it may be reached and worked with in the presence of a non-internalizable valuing and nurturing relationship which we label 'primary relatedness'. This relation is therefore the interactional context for emotional growth. Numerous clinical examples are provided to demonstrate characteristic features of this region of the mind as seen in psychoanalyses. Vignettes illustrate the experiences of patient and analyst as primary relatedness is established; the consequent re-emergence of traumatic states and unmet needs, often initially in the form of severe physical and psychological deterioration; primitive forms of symbolization in the course of repairing primal repression; and the role of action in emotional growth.

Adult↗

PubMedDate not supplied

[Use of catabolic repression in the selection of the glucoamylase-producer Aspergillus niger].

The effect of various carbon sources and cAMP on the glucoamylase synthesis in Aspergillus niger was studied to find carbon sources repressed the enzyme synthesis and conditions for the selection of catabolite stable mutants. Maltose at a concentration of 0.5% stimulated the glucoamylase synthesis, but at a concentration of 4% it repressed not only the enzyme synthesis but the growth of the parental strain on the agar medium. The more active mutant 66 was obtained as a result of treatment of Asp. niger st 6 with NG. This mutant is able to grow on the Czapek's medium containing maltose at concentrations 4 or 6%. The mutant 66 produced about 2.9 times more glucoamylase than its parent when maltose was added at 0.5% concentration to the medium. The glucoamylase synthesis in the parental strain was completely repressed under repressing conditions, while the level of the mutant strain activity was 35% from the level of enzyme activity on the medium without the repressor. The addition of cAMP (5.10(-5] resulted in a partial release of maltose (4%) repression of the glucoamylase synthesis in both strains. The results obtained indicate a possibility to select Asp niger mutants with the partially derepressed glucoamylase synthesis. Other regulation mechanisms in addition to catabolite repression may be involved in the regulation of the glucoamylase synthesis.

Aspergillus niger↗

PubMed1996

Partial repression of human gamma-globin genes by LCR element HS3 when linked to beta-globin genes and LCR element HS2 in MEL cells.

Clues for overcoming fetal (gamma-) globin gene repression in adult human erythroid cells may come from understanding why repression of isolated gamma-globin genes has not previously been achieved in the adult erythroid environment of mouse erythroleukemia cells (MEL). Repression of human gamma-globin genes has been demonstrated in MEL cells when transferred as part of the entire beta-globin gene cluster packaged in chromatin. Major differences in these approaches are prior packaging into chromatin and the presence of additional sequences, notably from the locus control region (LCR). In this report we focus on the contribution to gamma-globin gene repression that multiple elements of the LCR may have. We first show preferential activation of beta-globin genes over gamma-globin genes in MEL cells when linked to each other and to LCR sequences containing the core elements of DNase I hypersensitive sites 4, 3, and 2. Removal of the HS4 element had no effect, however, removal of the 225 bp HS3 core element resulted in a five-fold increase in gamma-globin gene expression. The enhancer 3' to the A gamma-globin gene also had no apparent effect on gamma-globin gene expression. These results provide first evidence of gamma-globin gene repression involving the core region of HS3 in the presence of the core region of HS2 and a beta-globin gene. A mechanism for repression involving sequestration of the gamma-promoter away from the strong enhancer activity of HS2 is proposed.

Animals↗

PubMed1992

Identification of a non-basic domain in the histone H4 N-terminus required for repression of the yeast silent mating loci.

We have shown previously that a stretch of four charged residues (16-19) at the histone H4 N-terminus is involved in repression of the yeast silent mating loci. One of these residues, Lys16, is a site for acetylation, which may prevent repression of the silent mating loci. In this paper we ask whether other sequences in histone H4, possibly in conjunction with H3 residues, are required for repression. We find that even in combination, the other seven acetylatable lysines in H3 and H4 do not function in repression. In contrast, we have found that an adjacent relatively uncharged domain (residues 21-29) is required for repression and that single amino acid insertions and deletions in this region are extremely detrimental. We propose that the basic and non-basic domains together form a DNA (or protein) induced amphipathic alpha-helix required in the formation of a repressive chromatin structure.

Acetylation↗

PubMed1994

c-Myc represses transcription in vivo by a novel mechanism dependent on the initiator element and Myc box II.

We show that c-Myc, in addition to activating transcription through E-box Myc binding sites (Ems), also represses transcription by a mechanism dependent on initiator (Inr) elements of the basal promoters of susceptible genes. Repression was first observed as a component of c-Myc biphasic regulation of the adenovirus-2 major late promoter (MLP), which contains both Inr and Ems sequences. Two differentiation-specific genes containing Inr, the C/EBP alpha and albumin genes, are repressed through their basal promoters by c-Myc, but are activated by the related B-HLH-LZ factor, USF. Repression requires both the B-HLH-LZ and Myc box II (MBII) domains. Significantly, a MBII deletion mutant which is deficient in repression, but transactivates normally, fails to cooperate with an activated ras gene to transform primary fibroblasts. Thus Myc-dependent transactivation is insufficient for Ras cooperation and the novel transcription repression function is implicated in Ras cooperation as well as the suppression of Inr-dependent genes.

Adenoviridae↗

PubMed2005

Retinoic acid induced repression of AP-1 activity is mediated by protein phosphatase 2A in ovarian carcinoma cells.

In previous studies we have shown that all-trans retinoic acid (atRA)-treatment of the atRA-sensitive ovarian carcinoma cell line CA-OV3 repressed AP-1 activity by about 50%, while a similar effect was not observed in the atRA-resistant ovarian carcinoma cell line, SK-OV3. These results suggested that the repression of AP-1 activity may be one of the mechanisms by which atRA inhibits the growth of atRA-sensitive CA-OV3 cells. In the present studies, we investigated further the molecular mechanism by which AP-1 activity is repressed by atRA. We show that the repression of AP-1 activity correlates with an increase in JunB protein expression and a decrease in N-terminal phosphorylation of c-Jun. The decrease in N-terminal phosphorylation of c-Jun does not appear to be modulated by JNK or ERK, since their protein expression patterns and kinase activity do not correlate with the repression of AP-1 activity following treatment with atRA. However, the activity of the protein phosphatase PP2A was found to increase 24 h following atRA treatment in CA-OV3 cells. Moreover, the catalytic subunit of PP2A was found to associate with c-Jun in vivo following atRA treatment. Since the inhibition of AP-1 activity following atRA treatment of CA-OV3 cells was abolished in the presence of specific PP2A inhibitors, it is likely that PP2A plays an important role in the atRA-induced repression of AP-1.

Carcinoma↗

PubMed1993

Synaptic repression at crayfish neuromuscular junctions. II. Evidence for calcium involvement.

The inability of synaptic junctions to generate normalisized postsynaptic potentials under normal physiological conditions was studied at crayfish neuromuscular synapses. Synaptic repression in the superficial flexor muscle system of the crayfish was induced by surgery: the nerve was cut in the middle of the target field, and the lateral muscle fibers were removed. After this surgery, the remaining medial synapses were unable to generate normal-sized junction potentials (jp) over the medial muscle population. In an attempt to study the mechanisms underlying this response, we varied the extracellular calcium concentration of the Ringers solution bathing the preparation, in both repressed and control animals, while monitoring the size of the same junction potential. The junction potential generated by the spontaneous activity of the nerve increased in size with increasing calcium concentrations in control animals, but failed to do so in repressed animals, that is, changes in external calcium concentrations did not affect repressed synapses. However, in the presence of the calcium ionophore A23187, control and repressed synapses both show an increase in the junction potential sizes they generate. Our data suggest that calcium is involved in the mechanisms that underlie synaptic repression in this crustacean neuromuscular system.

Animals↗