Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “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 703 records · Page 39Linked to original sources
PubMed1975

Transient repression of catabolite-sensitive enzyme synthesis elicited by 2,4-dinitrophenol.

Transient inhibition of catabolic enzyme synthesis in Escherichia coli occurred when a low concentration of 2,4-dinitrophenol (DNP) was simultaneously added with inducer. Using mutant strains defective for gamma-gene product or constitutive for lac enzymes, it was found that the inhibition is not due to the exclusion of inducer by uncoupling. The addition of cyclic adenosine 3',5'-monophosphate overcame repression. The components of the lac operon coordinately responded to DNP inhibition. From deoxyribonucleic acid-ribonucleic acid hybridization experiments, it was found that the inhibition of beta-galactosidase induction occurred at the level of messenger ribonucleic acid synthesis specific for the lac operon. It seems probable that DNP represses induction in a similar manner to that of transient repression observed upon the addition of glucose. Furthermore, it was found that transient repression disappeared if cells were preincubated with DNP before induction. This indicates that new contact of cells with DNP is obligatory for transient repression. From these results, it is suggested that the cell membrane may be responsible for regulation of catabolite-sensitive enzyme synthesis.

Biological Transport, Active↗
PubMed1978

Regulation of lac operon expression: reappraisal of the theory of catabolite repression.

The physiological state of Escherichia coli with respect to (permanent) catabolite repression was assessed by measuring the steady-state level of beta-galactosidase in induced or in constitutive cells under a variety of growth conditions. Four results were obtained. (i) Catabolite repression had a major effect on fully induced or constitutive expression of the lac gene, and the magnitude of this effect was found to be dependent on the promoter structure; cells with a wild-type lac promoter showed an 18-fold variation in lac expression, and cells with the lacP37 (formerly lac-L37) promoter exhibited several hundred-fold variation. (ii) Exogenous adenosine cyclic 3',5'-monophosphoric acid (cAMP) could not abolish catabolite repression, even though several controls demonstrated that cAMP was entering the cells in significant amounts. (Rapid intracellular degradation of cAMP could not be ruled out.) (iii) Neither the growth rate nor the presence of biosynthetic products altered the degree of catabolite repression; all variation could be related to the catabolites present in the growth medium. (iv) Slowing by imposing an amino acid restriction decreased the differential rate of beta-galactosidase synthesis from the wild-type lac promoter when bacteria were cultured in either the absence or presence of cAMP; this decreased lac expression also occurred when the bacteria harbored the catabolite-insensitive lacP5 (formerly lacUV5) promoter mutation. These findings support the idea that (permanent) catabolite repression is set by the catabolites in the growth medium and may not be related to an imbalance between catabolism and anabolism.

Culture Media↗
PubMed1980

Regulation of aromatic amino acid biosynthesis in Escherichia coli K-12: control of the aroF-tyrA operon in the absence of repression control.

Evidence was found which indicated that a mutation in gene trpS affected the rate of synthesis of tyrosine-repressible 3-deoxy-D-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase. The effect was found to occur independently of repression mediated by the tyrR gene product, and it was not due to a change in growth rate, nor was it a manifestation of the stringent response. It is proposed that in the proximal region of the aroF-tyrA operon there is an attenuator site controlled by the level of charged tryptophanyl-transfer RNA. In addition, it was demonstrated that starvation for certain amino acids led to degradation of tyrosine-repressible DAHP synthetase, but not phenylalanine-repressible DAHP synthetase, and supplementation with the missing amino acid led to an increased rate of synthesis of tyrosine-repressible DAHP synthetase during subsequent growth.

Amino Acids↗
PubMed1981

Structure and function of the PHO82-pho4 locus controlling the synthesis of repressible acid phosphatase of Saccharomyces cerevisiae.

pho4 mutants of Saccharomyces cerevisiae, although rare among phosphatase-negative mutants isolated from wild-type strains, were isolated efficiently from pho80, pho85, or pho80 pho85 strains. The distribution of these pho4 mutants over the pho4 locus was determined by analyzing random spores of two- and three-factor crosses. The pho4-4 mutation confers temperature-sensitive synthesis of repressible acid phosphatase. An intragenic suppressor for the pho4-12 allele results in the temperature-sensitive synthesis of repressible acid phosphatase. Recombination between these sites occurs at 1.0 to 3.0%, the highest for any pair of sites within the pho4 locus. All these results strongly indicate that the information of the pho4 locus is translated into a protein. The PHO82 site was mapped inside the pho4 locus by random spore analysis. The order met10-pho4-1PHO82-1-pho4-9 on the right arm of chromosome VI was confirmed by tetrad analysis. Doubly heterozygous diploids, pho3 PHO82c PHO4+/pho3 pho82+ pho4, produce variable amounts of repressible acid phosphatase under repressive conditions depending on the combination of PHO82c and pho4 alleles. This phenomenon may reflect the constitutive production of the pho82+-pho4 product in the repressed condition, which interferes with the function of the PHO82c-PHO4+ product. The earlier model for the function of the PHO82-pho4 cluster, in which the PHO82 site acts as an operator of the pho4 gene, has been revised to a model in which the PHO82 site codes for the part of the pho4 protein that has affinity for the regulatory protein encoded by the pho80 and pho85 genes.

Acid Phosphatase↗
PubMed1983

Effects of aerobic and anaerobic shock on catabolite repression in cyclic AMP suppressor mutants of Escherichia coli.

Cultures of Escherichia coli K-12 grown on glucose or gluconate under aerobic conditions exhibited catabolite repression of beta-galactosidase synthesis. Depression occurred when these cultures were subjected to anaerobic shock. These states of repression and depression were found to be associated with low and high differential rates of cyclic AMP synthesis, respectively. This observation is consistent with the view that cyclic AMP plays a central role in the catabolite repression phenomenon. We report here, however, that identical stages of repression and derepression occur in mutant strains possessing cya crp(Csm) genotypes and therefore unable to synthesize cyclic AMP. These results suggest that cyclic AMP is not the sole regulator involved in catabolite repression.

Aerobiosis↗
PubMed1983

Repressible extracellular phosphodiesterases showing cyclic 2',3'- and cyclic 3',5'-nucleotide phosphodiesterase activities in Neurospora crassa.

Two molecular species of repressible extracellular phosphodiesterases showing cyclic 2',3'- and cyclic 3',5'-nucleotide phosphodiesterase activities were detected in mycelial culture media of wild-type Neurospora crassa and purified. The two molecular species were found to be monomeric and polymeric forms of an enzyme constituted of identical subunits having molecular weights of 50,000. This enzyme had the same electrophoretic mobility as repressible acid phosphatase. The enzyme designated repressible cyclic phosphodiesterase showed pH optima of 3.2 to 4.0 with a cyclic 3',5'-AMP substrate and 5.0 to 5.6 with a cyclic 2',3'-AMP substrate. Repressible cyclic phosphodiesterase was activated by MnCl2 and CoCl2 with cyclic 2',3'-AMP as substrate and was slightly activated by MnCl2 with cyclic 3',5'-AMP. The enzyme hydrolyzed cyclic 3',5'- and cyclic 2',3'-nucleotides, in addition to bis-rho-nitrophenyl phosphate, but not certain 5' -and 3'-nucleotides. 3'-GMP and 3'-CMP were hydrolyzed less efficiently. Mutant strains A1 (nuc-1) and B1 (nuc-2), which cannot utilize RNA or DNA as a sole source of phosphorus, were unable to produce repressible cyclic phosphodiesterase. The wild type (74A) and a heterocaryon between strains A1 and B1 produced the enzyme and showed growth on orthophosphate-free media containing cyclic 2',3'-AMP or cyclic 3',5'-AMP, whereas both mutants showed little or no growth on these media.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1984

Saccharomyces cerevisiae mutants provide evidence of hexokinase PII as a bifunctional enzyme with catalytic and regulatory domains for triggering carbon catabolite repression.

A selection system has been devised for isolating hexokinase PII structural gene mutants that cause defects in carbon catabolite repression, but retain normal catalytic activity. We used diploid parental strains with homozygotic defects in the hexokinase PI structural gene and with only one functional hexokinase PII allele. Of 3,000 colonies tested, 35 mutants (hex1r) did not repress the synthesis of invertase, maltase, malate dehydrogenase, and respiratory enzymes. These mutants had additional hexokinase PII activity. In contrast to hex1 mutants (Entian et al., Mol. Gen. Genet. 156:99-105, 1977; F.K. Zimmermann and I. Scheel, Mol. Gen. Genet. 154:75-82, 1977), which were allelic to structural gene mutants of hexokinase PII and had no catalytic activity (K.-D. Entian, Mol. Gen. Gent. 178:633-637, 1980), the hex1r mutants sporulated hardly at all or formed aberrant cells. Those ascospores obtained were mostly inviable. As the few viable hex1r segregants were sterile, triploid cells were constructed to demonstrate allelism between hex1r mutants and hexokinase PII structural gene mutants. Metabolite concentrations, growth rate, and ethanol production were the same in hex1r mutants and their corresponding wild-type strains. Recombination of hexokinase and glucokinase alleles gave strains with different specific activities. The defect in carbon catabolite repression was strongly associated with the defect in hexokinase PII and was independent of the glucose phosphorylating capacity. Hence, a secondary effect caused by reduced hexose phosphorylation was not responsible for the repression defect in hex1 mutants. These results, and those with the hex1r mutants isolated, strongly supported our earlier hypothesis that hexokinase PII is a bifunctional enzyme with (i) catalytic activity and (ii) a regulatory component triggering carbon catabolite repression (Entian, Mol. Gen. Genet. 178:633-637, 1980; K.-D. Entian and D. Mecke, J. Biol. Chem. 257:870-874, 1982).

Alleles↗
PubMed1984

Gratuitous repression of avtA in Escherichia coli and Salmonella typhimurium.

avtA , which encodes transaminase C (alanine-valine transaminase), is repressed by excess-L-alanine or L-leucine, and also by limitation for any of a number of amino acids in Escherichia coli and Salmonella typhimurium. Amino acid limitation causes repression by promoting the accumulation of L-alanine or L-leucine or both. avtA is also repressed by L-alpha-aminobutyric acid and other nonprotein amino acids which are structurally similar to L-alanine. We hypothesize that L-alanine and L-alpha-aminobutyric acid, whose syntheses are catalyzed by transaminase C, are the true corepressors of avtA . Repression by structural analogs of the true corepressors is termed gratuitous repression.

Alanine↗
PubMed1989

Bacillus licheniformis alpha-amylase gene, amyL, is subject to promoter-independent catabolite repression in Bacillus subtilis.

Expression of the Bacillus licheniformis alpha-amylase gene, amyL, was temporally activated and subject to catabolite repression both in its natural host and when cloned on a 3.55-kilobase fragment in Bacillus subtilis. A subclone from which the promoter region of amyL and sequences upstream from the promoter were deleted had a low level of amylase activity. Expression of the promoterless gene was still subject to repression by glucose when the gene was present either on a multicopy plasmid or integrated into the B. subtilis chromosome. Catabolite repression occurred independently of the amylase promoter and irrespective of the distance of the promoterless amyL gene from the promoter which transcribed it. The transcriptional start sites of amyL activated by its own promoter and by a vector sequence promoter were determined by S1 mapping. alpha-Amylase-specific mRNA levels were measured in repressing and nonrepressing media, and catabolite repression was found to act at the level of transcription.

Bacillus↗
PubMed1989

Concentration-dependent repression of the soluble and membrane components of the Streptococcus mutans phosphoenolpyruvate: sugar phosphotransferase system by glucose.

Growth of Streptococcus mutans Ingbritt in continuous culture (pH 7.0, dilution rate of 0.1 h-1) at medium glucose concentrations above 2.6 mM resulted in repression of the sugar-specific membrane components, enzyme IIGlc (EIIGlc) and EIIMan, of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). In one experiment, significant repression (27-fold) was observed with 73 mM glucose when the glycolytic capacity of the cells was reduced by only 2-fold and when the culture was still glucose limited. In a more comprehensive experiment in which cells were grown in continuous culture at eight glucose concentrations from 2.6 to 304 mM, in addition to repression of specific EII activities for glucose, mannose, 2-deoxyglucose, and fructose, synthesis of the general protein, EI, was repressed at all glucose levels above 2.6 mM to a maximum of 4-fold at 304 mM glucose when the culture was growing with excess glucose (i.e., nitrogen limited). The other PTS general protein, HPr, was less sensitive to the exogenous glucose level but was nevertheless repressed fourfold under glucose-excess conditions. The Km for glucose for EIIGlc increased from 0.22 mM during growth at 3.6 mM glucose (glucose limited) to 0.48 mM at 271 mM glucose (glucose excess). The shift from heterofermentation to homofermentation during growth with increasing glucose levels suggests the involvement of glycolytic intermediates, ATP, or another high-energy phosphate metabolite in regulation of the synthesis of the PTS components in S. mutans.

Bacterial Proteins↗
PubMed1991

Extragenic suppressors of yeast glucose derepression mutants leading to constitutive synthesis of several glucose-repressible enzymes.

Saccharomyces cerevisiae regulatory genes CAT1 and CAT3 constitute a positive control circuit necessary for derepression of gluconeogenic and disaccharide-utilizing enzymes. Mutations within these genes are epistatic to hxk2 and hex2, which cause defects in glucose repression. cat1 and cat3 mutants are unable to grow in the presence of nonfermentable carbon sources or maltose. Stable gene disruptions were constructed inside these genes, and the resulting growth deficiencies were used for selecting epistatic mutations. The revertants obtained were tested for glucose repression, and those showing altered regulatory properties were further investigated. Most revertants belonged to a single complementation group called cat4. This recessive mutation caused a defect in glucose repression of invertase, maltase, and iso-1-cytochrome c. Additionally, hexokinase activity was increased. Gluconeogenic enzymes are still normally repressible in cat4 mutants. The occurrence of recombination of cat1::HIS3 and cat3::LEU2 with some cat4 alleles allowed significant growth in the presence of ethanol, which could be attributed to a partial derepression of gluconeogenic enzymes. The cat4 complementation group was tested for allelism with hxk2, hex2, cat80, cid1, cyc8, and tup1 mutations, which were previously described as affecting glucose repression. Allelism tests and tetrad analysis clearly proved that the cat4 complementation group is a new class of mutant alleles affecting carbon source-dependent gene expression.

Alleles↗
PubMed1996

Significance of HPr in catabolite repression of alpha-amylase.

CcpA and HPr are presently the only two proteins implicated in Bacillus subtilis global carbon source catabolite repression, and the ptsH1 mutation in the gene for the HPr protein was reported to relieve catabolite repression of several genes. However, alpha-amylase synthesis by B. subtilis SA003 containing the ptsH1 mutation was repressed by glucose. Our results suggest HPr(Ser-P) may be involved in but is not required for catabolite repression of alpha-amylase, indicating that HPr(Ser-P) is not the sole signaling molecule for CcpA-mediated catabolite repression in B. subtilis.

Bacillus subtilis↗
PubMed1966

Altered end-product patterns and catabolite repression in Escherichia coli.

Dobrogosz, Walter J. (North Carolina State University, Raleigh). Altered end-product patterns and catabolite repression in Escherichia coli. J. Bacteriol. 91:2263-2269. 1966.-End products formed during growth of Escherichia coli ML30 on glucose were examined under various conditions known to promote or prevent catabolite repression of the inducible beta-galactosidase system in this organism. Cultures were grown under these conditions in the presence of C(14)-glucose or C(14)-pyruvate. The products formed were assayed isotopically after separation on columns of silicic acid. Under conditions known to promote catabolite repression, glucose was degraded primarily to acetate and CO(2). When repression was turned off by anaerobic shock, glucose metabolism was characterized by the accumulation of ethyl alcohol in addition to acetate and CO(2). The results presented in this report indicate that oxidative decarboxylation of pyruvate may markedly affect the amount of energy that can be derived from glucose catabolism. In turn, the amount of energy derived from catabolic processes may play a key role in the mechanism of catabolite repression.

Acetates↗
PubMed1968

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

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

Aminopterin↗
PubMed1969

Molecular basis of transient repression of beta-galactosidase in Escherichia coli.

The molecular basis of transient repression of beta-galactosidase by glucose was examined. This repression acted only at the level of transcription. Apparently, it was not mediated by the I-gene product. Analysis of single cells in a culture subjected to transient repression showed that essentially all cells initially experienced repression and later became gradually resistant to repression.

Bacterial Proteins↗
PubMed2002

Native and recombinant polycomb group complexes establish a selective block to template accessibility to repress transcription in vitro.

Polycomb group (PcG) proteins are responsible for stable repression of homeotic gene expression during Drosophila melanogaster development. They are thought to stabilize chromatin structure to prevent transcription, though how they do this is unknown. We have established an in vitro system in which the PcG complex PRC1 and a recombinant PRC1 core complex (PCC) containing only PcG proteins are able to repress transcription by both RNA polymerase II and by T7 RNA polymerase. We find that assembly of the template into nucleosomes enhances repression by PRC1 and PCC. The subunit Psc is able to inhibit transcription on its own. PRC1- and PCC-repressed templates remain accessible to Gal4-VP16 binding, and incubation of the template with HeLa nuclear extract before the addition of PCC eliminates PCC repression. These results suggest that PcG proteins do not merely prohibit all transcription machinery from binding the template but instead likely inhibit specific steps in the transcription reaction.

Animals↗
PubMed1987

GAL4 of Saccharomyces cerevisiae activates the lactose-galactose regulon of Kluyveromyces lactis and creates a new phenotype: glucose repression of the regulon.

A Kluyveromyces lactis mutant defective in lac9 cannot induce beta-galactosidase or galactokinase activity and is unable to grow on lactose or galactose. When this strain was transformed with the GAL4 positive regulatory gene of Saccharomyces cerevisiae it was able to grow on lactose or galactose as the sole carbon source. Transformants bearing GAL4 exhibited a 4.5-h generation time on galactose or lactose, versus 24 h for the nontransformed lac9 strain. A K. lactis lac9 strain bearing two integrated copies of GAL4 showed 3.5-fold induction of beta-galactosidase activity and 1.8-fold induction of galactokinase activity compared with 15.6-fold and 4.4-fold induction, respectively, for the LAC9 wild-type strain. In transformants bearing 10 integrated copies of GAL4, the induced level of beta-galactosidase was nearly as high as in the LAC9 wild-type strain. In addition to restoring lactose and galactose gene expression, GAL4 in K. lactis lac9 mutant cells conferred a new phenotype, severe glucose repression of lactose and galactose-inducible enzymes. Glucose repressed beta-galactosidase activity 35- to 74-fold and galactokinase activity 14- to 31-fold in GAL4 transformants, compared with the 2-fold glucose repression exhibited in the LAC9 wild-type strain. The S. cerevisiae MEL1 gene was repressed fourfold by glucose in LAC9 cells. In contrast, the MEL1 gene in a GAL4 lac9 strain was repressed 20-fold by glucose. These results indicate that the GAL4 and LAC9 proteins activate transcription in a similar manner. However, either the LAC9 or GAL4 gene or a product of these genes responds differently to glucose in K. lactis.

Enzyme Induction↗
PubMed1996

Ethical issues in the search for repressed memories.

Currently, concepts of repression and dissociation are in flux. It has been pointed out that there is no scientific evidence for the occurrence of repression and that the whole notion is anecdotal. Dissociation, which is offered as an alternative to repression, cannot logically be held to operate without a motive force, as Freud argued, or a weakness of the organism, as Janet proposed. The concepts have been applied particularly to the idea that early childhood experience could be repressed but recovered many years later. This claim is at variance with established knowledge concerning human memory. Practices of subtle and overt suggestion, employed in recovered-memory treatments, give rise to a false-memory syndrome in which individuals, who have undergone various levels of suggestion, accuse their parents and others of childhood sexual abuse. The common phenomenon of childhood sexual abuse is contaminated by many cases that may be regarded on strong grounds as being false and have been retracted in more than 1,000 instances. Repressed-memory (RM) treatment is also at variance with traditional psychotherapy, which does not encourage confrontation on the basis of uncorroborated information; moreover, many cases of RM therapy seem to result in deterioration. Unlike traditional psychotherapy, some RM practitioners strongly encourage patients to hate individuals in their family circle. The consequences of these developments, the need for informed consent, and the development of legislative initiatives to challenge RM therapy are noted. The impact of these therapies and proposed legislation upon regular psychotherapy and psychiatry is outlined.

Child↗