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At least 937 records · Page 52Linked to original sources
PubMed1980

In vitro synthesis of repressible yeast acid phosphatase: identification of multiple mRNAs and products.

Antibodies to repressible nonspecific acid phosphatase [APase; orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2] purified from Saccharomyces cerevisiae were used to detect the in vitro products of APase mRNA. Immunoprecipitation of cell-free synthesized protein and of in vivo enzyme from cell extracts has shown that derepression of enzyme synthesis in situ is the result of de novo appearance of functional mRNA followed by de novo protein synthesis. At least three unique APase polypeptides are synthesized in vitro from separate mRNAs and appear to be glycosylated in vivo to form secreted enzyme.

Acid Phosphatase↗
PubMed1998

p53 is a general repressor of RNA polymerase III transcription.

p53 is a major tumour suppressor that is inactivated in a large proportion of human cancers. We show that p53 serves as a general repressor of transcription by RNA polymerase (pol) III. It can inhibit the synthesis of a range of essential small cellular RNAs including tRNA, 5S rRNA and U6 snRNA, as well as viral products such as the adenovirus VAI RNA. Fibroblasts derived from p53 knock-out mice display a substantial increase in pol III transcriptional activity. Endogenous cellular p53 is shown to interact with the TATA-binding protein (TBP)-containing general factor TFIIIB, thereby compromising its function severely. However, assembly of TFIIIB into a pre-initiation complex confers substantial protection against the inhibitory effects of p53. Since TFIIIB is an essential determinant of the biosynthetic capacity of cells, its release from repression by p53 may contribute to a loss of growth control during the development of many tumours.

3T3 Cells↗
PubMed1999

Novel alleles of yeast hexokinase PII with distinct effects on catalytic activity and catabolite repression of SUC2.

In the yeast Saccharomyces cerevisiae, glucose or fructose represses the expression of a large number of genes. The phosphorylation of glucose or fructose is catalysed by hexokinase PI (Hxk1), hexokinase PII (Hxk2) and a specific glucokinase (Glk1). The authors have shown previously that either Hxk1 or Hxk2 is sufficient for a rapid, sugar-induced disappearance of catabolite-repressible mRNAs (short-term catabolite repression). Hxk2 is specifically required and sufficient for long-term glucose repression and either Hxk1 or Hxk2 is sufficient for long-term repression by fructose. Mutants lacking the TPS1 gene, which encodes trehalose 6-phosphate synthase, can not grow on glucose or fructose. In this study, suppressor mutations of the growth defect of a tps1delta hxk1delta double mutant on fructose were isolated and identified as novel HXK2 alleles. All six alleles studied have single amino acid substitutions. The mutations affected glucose and fructose phosphorylation to a different extent, indicating that Hxk2 binds glucose and fructose via distinct mechanisms. The mutations conferred different effects on long- and short-term repression. Two of the mutants showed very similar defects in catabolite repression, despite large differences in residual sugar-phosphorylation activity. The data show that the long- and short-term phases of catabolite repression can be dissected using different hexokinase mutations. The lack of correlation between in vitro catalytic hexokinase activity, in vivo sugar phosphate accumulation and the establishment of catabolite repression suggests that the production of sugar phosphate is not the sole role of hexokinase in repression. Using the set of six hxk2 mutants it was shown that there is a good correlation between the glucose-induced cAMP signal and in vivo hexokinase activity. There was no correlation between the cAMP signal and the short- or long-term repression of SUC2, arguing against an involvement of cAMP in either stage of catabolite repression.

Alleles↗
PubMed1983

Study of the positive control of the general amino-acid permease and other ammonia-sensitive uptake systems by the product of the NPR1 gene in the yeast Saccharomyces cerevisiae.

Mutations at the NPR1 genetic locus are known to inactivate (totally or partially) at least five distinct ammonia-sensitive permeases. Mutants with thermosensitive NPR1 gene product (nprts) have been used to discriminate between three possible roles of this protein, namely (a) a common constituent of a set of ammonia-sensitive permeases; (b) a common activator of these permeases; (c) a common positive factor necessary for their synthesis. Inactivation of the general amino-acid permease was observed upon transfer of nprts mutant cells to a non-permissive temperature. Under the same conditions, the general amino-acid permease of the wild-type cells remained active for several hours even when protein synthesis was inhibited by nitrogen starvation or by cycloheximide. Mutations at three unlinked loci, namely the PGR site (located in the GAP1 structural gene of the permease), and the unlinked MUT2 and MUT4 loci restore the general amino-acid permease activity in npr1 mutants. The results are interpreted as indicating that the NPR1 product is necessary for the reactivation of the general amino-acid permease which seems to be continuously inactivated by a regulatory process mediated by the MUT2 and the MUT4 gene products acting at the level of the PGR site of the general amino-acid permease molecule. The proline permease and the ureidosuccinic-acid permease seem to be subject to the same double regulation by inactivation-reactivation of the permeases and by repression of their synthesis. A tentative scheme of the regulation of the general amino-acid permease is presented.

Amino Acid Transport Systems↗
PubMed1978

Repression of Escherichia coli pyridine nucleotide transhydrogenase by leucine.

Addition of 0.1% casein hydrolysate to a minimal growth medium decreased membrane-bound transhydrogenase activity in Escherichia coli by about 80%. Of the amino acids added individually to the growth medium, only leucine and, to a lesser extent, methionine and alanine were effective, alpha-Ketoisocaproate- and leucine-containing peptides repressed the activity, and leucine also repressed activity in adenyl cyclase-deficient and relaxed strains. Derepression of transhydrogenase followed the removal of leucine from the growth medium and was sensitive to rifampin and chloramphenicol. A phosphoglucoisomerase-deficient strain that was forced to use the hexose monophosphate shunt exclusively had normal levels of transhydrogenase, which was repressed by leucine. Transhydrogenase activity doubled in mutants lacking either of the shunt dehydrogenases but was still repressed by leucine. In strains constitutive for the leucine biosynthetic operon, transhydrogenase was repressed by leucine but in strains livR and lst R, with leucine transport resistant to leucine repression, transhydrogenase was not repressed by leucine. These data suggest that transhydrogenase may have a function in the transport of branched-chain amino acids. In a hisT strain (which has altered leucyl-tRNA), transhydrogeanse was at a repressed level without the addition of leucine, suggesting that leucyl-tRNA may be involved in the regulation.

Biological Transport, Active↗
PubMed1998

glkA is involved in glucose repression of chitinase production in Streptomyces lividans.

Chitinase production in Streptomyces lividans is induced by chitin and repressed in the presence of glucose. A mutant of S. lividans TK24, strain G015, which was defective in glucose repression of chitinase production, was obtained by screening colonies for zones of clearing on colloidal chitin agar plates containing 1.0% (wt/vol) glucose. The transcriptional analysis of chiA in G015 with xylE, which encodes catechol 2,3-dioxygenase, as a reporter gene showed that the transcription from the chiA promoter of S. lividans TK24 occurred regardless of the presence of glucose. G015 was resistant to 2-deoxyglucose (2-DOG) and did not utilize glucose as a sole carbon source. When a DNA fragment containing glkA, a gene for glucose kinase, of Streptomyces coelicolor A3(2) was introduced into strain G015 on a low-copy-number plasmid, the sensitivity to 2-DOG, the ability to utilize glucose, and the glucose repression of chitinase production were restored. These results indicate that glkA is involved in glucose repression of chitinase production in S. lividans TK24.

Bacterial Proteins↗
PubMed1998

Expression of the bglH gene of Lactobacillus plantarum is controlled by carbon catabolite repression.

A newly identified bglH gene coding for a phospho-beta-glucosidase of Lactobacillus plantarum was isolated and expressed in Escherichia coli. The sequence analysis of the cloned DNA fragment showed an open reading frame encoding a 480-amino-acid protein with a calculated molecular mass of 53 kDa. The bglH gene was shown to be expressed on a monocistronic transcriptional unit. Its transcription was repressed 10-fold in L. plantarum cells grown on glucose compared to the beta-glucoside salicin as a sole carbon source. A catabolite-responsive element (CRE) spanning from -3 to +11 with respect to the transcriptional start point was found, and its functionality was assessed by mutational analysis. In vitro and in vivo DNA binding experiments suggested the occurrence of a DNA-protein complex at the CRE site, which would mediate glucose repression of bglH expression.

Amino Acid Sequence↗
PubMed1969

Autoregulation of the synthesis of nitrate reductase in Aspergillus nidulans.

In Aspergillus nidulans, the syntheses of nitrate and nitrite reductases are induced by nitrate, and are repressed by ammonium. It is possible in wild-type strains to overcome partially the repressive effect of ammonium, by the addition of high concentrations of nitrate to the growth medium. Mutations which lead to the production of abnormal nitrate reductase affect in addition the control of the synthesis of the nitrate-metabolizing enzymes, which in these strains are produced constitutively. That this is not due to the accumulation of an internal inducer has now been shown, as these mutants have been found to be unable to respond to nitrate induction in the presence of ammonium in the same way as do wild-type strains. To explain these findings, we propose that the nitrate reductase molecule provides the recognition site for nitrate in the control system, such that when it is not complexed with nitrate it acts as a co-repressor, and, when it is complexed, as a co-inducer.

Aspergillus↗
PubMed1977

Reduced synthesis of beta-galactosidase in Escherichia coli infected with phage phi X 174.

The synthesis of beta-galactosidase (EC 3.2.1.23;beta-D-galactoside galactohydrolase) in E. coli was repressed as a result of infection with single-stranded DNA phage phi chi 174. Evidence is presented to show that this repression was not due to the restricted entry of the inducer molecules into the infected cells but to some phage-specified product(s). It was further shown that either the infected cells synthesized a fewer number of enzyme-specific mRNA or all such molecules were translated with a reduced efficiency; the half-lives of the mRNA's remained more or less unaffected.

Cell Membrane Permeability↗
PubMed1979

Alcohol dehydrogenase (ADH) in yeasts. II. NAD+-and NADP+-dependent alcohol dehydrogenases in Saccharomycopsis lipolytica.

In Sm. lipolytica one NAD+-dependent and three NADP+-dependent alcohol dehydrogenases are detectable by polyacrylamide gelelectrophoresis. The NAD+-dependent ADH (ADH I), with a molecular weight of 240,000 daltons, reacts more intensively with long-chain alcohols (octanol) than with short-chain alcohols (methanol, ethanol). The ADH I is not or only minimally subject to glucose repression. Besides the ADH I band no additional inducible NAD+-dependent ADH band is gel-electrophoretically detectable during growth of yeast cells in medium containing ethanol or paraffin. The ADH I band is very probably formed by two ADH enzymes with the same electrophoretic mobility. The NADP+-dependent alcohol dehydrogenases (ADH II--IV) react with methanol, ethanol and octanol with different intensity. In polyacrylamide gradients two bands of NADP+-dependent ADH are detectable: one with a molecular weight of 70,000 daltons and the other with 120,000 daltons. The occurrence of the three NADP+-dependent alcohol dehydrogenases is regulated by the carbon source of the medium. Sm. lipolytica shows a high tolerance against allylalcohol. Resistant mutants can be isolated only at concentrations of 1 M allylalcohol in the medium. All isolates of allylalcohol-resistant mutants show identical growth in medium containing ethanol as the wild type strain.

Acetates↗
PubMed1977

Regulation of aromatic amino acid transport systems in Escherichia coli K-12.

The regulation of the aromatic amino acid transport systems was investigated. The common (general) aromatic transport system and the tyrosine-specific transport system were found to be subject to repression control, thus confirming earlier reports. In addition, tryosine- and tryptophan-specific transport were found to be enhanced by growth of cells with phenylalanine. The repression and enhancement of the transport systems was abolished in a strain carrying an amber mutation in the regulator gene tyrR. This indicates that the tyrR gene product, which was previously shown to be involved in regulation of aromatic biosynthetic enzymes, is also involved in the regulation of the aromatic amino acid transport systems.

Amino Acids↗
PubMed1976

Dual control of invertase biosynthesis in chemostat culture.

In a previous study on the chemostat culture of Saccharomyces carlsbergensis, maximum invertase specific activity was observed at an intermediate dilution rate. A possible regulation mechanism, assuming there are simultaneous effects of induction and repression on two sites of the operator loci for invertase formation, is proposed which might account for the observed curve of the dilution rate effect.

Enzyme Induction↗
PubMed1997

A sucrose repression element in the Phaseolus vulgaris rbcS2 gene promoter resembles elements responsible for sugar stimulation of plant and mammalian genes.

Protoplasts isolated from the primary leaves of Phaseolus vulgaris L. were used in transient expression experiments to identify promoter sequences of the P. vulgaris rbcS2 gene, encoding ribulose 1,5-bisphosphate carboxylase/oxygenase small subunit, concerned with sucrose repression. The protoplasts supported high rates of expression of the chloramphenicol acetyl transferase reporter gene fused to 1433 bp of the rbcS2 5' flanking sequences. Expression was repressed by 50 mM sucrose whereas that driven by control promoters was not. Assays of promoter deletions revealed that 203 bp 5' to the transcription start site were sufficient for high rates of sucrose-repressible expression. A -187 bp deletion supported much lower rates of expression and was not subject to sucrose repression. The -203 to -187 bp region contains sequences resembling elements involved in the sugar stimulation of transcription of other genes: the SURE (sucrose response element) of plant genes and the ChoRE (carbohydrate response element) of mammalian genes. A G-box (CACGTG) located at -200 to -205 was important for high levels of sucrose-repressible expression, since deletion of a nucleotide from this element in the context of the 1433 bp promoter gave much reduced expression. However, a modified G-box (CcCGTG) in the -203 bp fusion and adjacent vector sequences remained functional. Measurements of rbcS and chalcone synthase (CHS) transcript levels in the protoplasts indicated that 4 mM sucrose was sufficient to repress or stimulate the respective genes. Further experiments suggested that metabolism of 6-carbon sugars is the signal for rbcS repression and CHS stimulation.

Acyltransferases↗
PubMed1981

Chromatin fine structure of active and repressed genes.

Study of the structural organization of chromatin during transcription and replication may reveal important aspects of these processes. At the lowest level of organization, chromatin consists of a repeating subunit, the nucleosome (for reviews see refs 1-3). Electron microscopy indicates that the nucleosomes are arranged helically or form discrete superbeads, generating the familiar 250 A-300-A fibre. It has been suggested that this fibre is further folded into loops containing up to several hundred nucleosomes. Despite extensive study, the significance and fate of these nucleosomes remain obscure. We have used here micrococcal nuclease digestion to compare the structures of actively transcribing and inert chromatin of the genes coding for the major heat-shock protein of Drosophila melanogaster. The repressed hsp 70 genes were considerably more resistant to cleavage by micrococcal nuclease than their flanking regions and the bulk of chromatin. The active genes, previously shown to be more sensitive than the repressed genes, are also more susceptible to the nuclease than their 3'-flanking regions and bulk chromatin.

Animals↗
PubMed1979

Involvement of long-chain acyl coenzyme A for lipid synthesis in repression of acetyl-coenzyme A carboxylase in Candida lipolytica.

Mutant strains of Candida lipolytica defective in acyl-CoA synthetase II [acid:CoA ligase (AMP-forming), EC 6.2.1.3] have been isolated. The mutants fail to grow on fatty acid as a sole carbon source but are capable of incorporating exogenous fatty acid into cellular lipids. This observation, together with our previous finding that mutant strains defective in acyl-CoA synthetase I cannot incorporate exogenous fatty acid into cellular lipids but are able to degrade fatty acid via beta-oxidation, indicates the presence of two functionally distinct long-chain acyl-CoA pools in the cell--i.e., one for lipid synthesis and the other for beta-oxidation. Unlike the wild-type and the revertant strains as well as the mutants lacking acyl-CoA synthetase II, the mutants defective in acyl-CoA synthetase I do not exhibit the repression of acetyl-CoA carboxylase [acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] by exogenous fatty acid. Measurement of the two long-chain acyl-CoA pools with the aid of appropriate mutant strains has indicated that the long-chain acyl-CoA to be utilized for lipid synthesis, but not that to be degraded via beta-oxidation, is involved in the repression of acetyl-CoA carboxylase.

Acetyl-CoA Carboxylase↗