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PubMed1977

Relationship between culture density and catabolite repression of an inducible aliphatic amidase in a thermophilic bacillus.

A direct correlation between the absorbance of a thermophilic bacillus and specific amidase activity was observed, which was found to depend on the cell density of the culture rather than on the time of contact of the culture with the inducer. Dilution of high density cultures caused the specific amidase activity to decrease. Environmental factors such as pH, concentration of inducer or degree of aeration, and level of NH+4 and glutamate had no effect on amidase synthesis. The decrease in amidase activity upon dilution could not be ascribed to destruction by oxygen or by inactivation or decay. Several lines of evidence suggest that catabolite repression is responsible for the phenomenon described. Succinate-grown cultures gave a stronger dilution effect thatn glutamate-grown cells. The mutant strain E-21, relatively resistant to catabolite repression, did not show the characteristic dilution effect nor the direct correlation between absorbance and specific amidase activity.

Acetamides↗
PubMed1988

Characteristics of extracellular protein production by Staphylococcus simulans biovar staphylolyticus during aerobic and anaerobic growth.

Aerobic cultures of Staphylococcus simulans biovar staphylolyticus characteristically achieved about 17 times higher bacterial densities and produced about 7 times higher concentrations of exoprotein than did anaerobic cultures. However, total exoprotein secreted per unit of bacterial dry weight typically was 2.3 times greater for anaerobic cultures. As determined by SDS-PAGE, anaerobic cultures also produced a wider variety of exoproteins than did aerobic cultures. Three exoenzymes, a staphylolytic endopeptidase, a micrococcolytic hexosaminidase and a thiol protease, were completely repressed during anaerobic growth, which is further evidence for coordination of their production.

Aerobiosis↗
PubMed1989

Translational repression of TEM beta-lactamase synthesis as a response of Escherichia coli to heat shock.

As a result of a temperature shift-up from 30 degrees C to 42 degrees C, beta-lactamase synthesis in Escherichia coli carrying pBR322 ceased transiently, even though the level of beta-lactamase mRNA was not altered. pBR328-directed pre-beta-lactamase synthesis in an in vitro transcription-translation coupled system was also repressed by incubation at the higher temperature. Translation of the lacZ sequence from the amp translation start signal, inserted into the open reading frame vector pORF1, was also repressed transiently upon the temperature shift-up. Pre-heating of the in vitro coupled system at 45 degrees C specifically reduced its capacity for pre-beta-lactamase synthesis. This capacity was restored by the addition of a 160,000 x g supernatant prepared from E. coli grown at 30 degrees C, but not by the supernatant from the cells incubated at 42 degrees C. These and other results indicate that (i) the 160,000 x g supernatant contains a heat-labile protein(s) that is required for efficient initiation of the translation of pre-beta-lactamase mRNA, and (ii) the heat shock-induced repression of beta-lactamase synthesis is due to inactivation of the protein(s) in the 160,000 x g supernatant.

Ampicillin↗
PubMed1971

Control of diaminopimelate decarboxylase by L-lysine during growth and sporulation of Bacilluscereus.

l-Lysine caused repression of diaminopimelate decarboxylase synthesis in Bacillus cereus when grown in either a minimal defined medium (CDGS medium) or a complex defined medium (a modified lysine assay medium). When cells were grown in either of the two media, variations in the specific activity of the enzyme as a function of time were found to be correlated with the intracellular lysine pool size during growth. From all of the data presented, it seems reasonable to conclude that during growth the synthesis of diaminopimelate decarboxylase is probably regulated by the intracellular lysine pool size. The relationship between lysine pool concentration and the specific activity of the enzyme did not occur in sporulating cells. The specific activity of diaminopimelate decarboxylase started to decrease at the end of exponential growth and continued to decline until it became nondetectable at the time of dipicolinic acid synthesis and development of spore refractility. Throughout this time, the intracellular lysine pool size remained below that which allowed derepression of enzyme synthesis during exponential growth. The mechanism(s) responsible for the observed decrease in the specific activity of the enzyme at the end of exponential growth is unknown. A threefold rise in the intracellular diaminopimelic acid concentration occurred when there was little or no detectable enzyme activity at the time of dipicolinic acid synthesis. This accumulation of diaminopimelic acid may exert positive control on the synthesis of spore peptidoglycan, the major component of the spore cortex.

Acetone↗
PubMed1990

Sequences within an upstream activation site in the yeast enolase gene ENO2 modulate repression of ENO2 expression in strains carrying a null mutation in the positive regulatory gene GCR1.

Transcription of the yeast enolase gene ENO2 is reduced 20- to 50-fold in strains carrying a null mutation in the positive regulatory gene GCR1. A small deletion mutation within one of two upstream activation sites (UAS elements) in the 5'-flanking region of ENO2 permitted wild-type levels of ENO2 gene expression in a strain carrying the gcr1 null mutation. These data show that sequences required for UAS element activity in GCR1 strains were required to repress ENO2 expression in a gcr1 strain. Protein factors that specifically bound to this UAS/repression site were identified. We show that the DNA-binding protein ABFI (autonomously replicating sequence-binding factor) is the major protein which binds the UAS/repression site. Minor DNA-binding activities that interact specifically with the UAS/repression site were also identified and may correspond to proteolytic breakdown products of ABFI. None of the observed binding activities were encoded by the GCR1 structural gene. A double-stranded oligonucleotide that included the UAS/repression site activated transcription of UAS-less ENO1 and ENO2 gene cassettes in vivo to wild-type levels in strains carrying the GCR1 allele as well as the gcr1 null mutation. These latter data show that the UAS/repression site is sufficient for transcriptional activation but is not sufficient to repress transcription of the enolase genes in a gcr1 genetic background.

Base Sequence↗
PubMed1991

Synthesis and properties of lignin peroxidase from Streptomyces viridosporus T7A.

The production of lignin peroxidase by Streptomyces viridosporus T7A was studied in shake flasks and under aerobic conditions in a 7.5-L batch fermentor. Lignin peroxidase synthesis was found to be strongly affected by catabolite repression. Lignin peroxidase was a non-growth-associated, secondary metabolite. The maximum lignin peroxidase activity was 0.064 U/mL at 36 h. In order to maximize lignin peroxidase activity, optimal conditions were determined. The optimal incubation temperature, pH, and substrate (2,4-dichlorophenol) concentration for the enzyme assays were 45 degrees C, 6, and 3 mM, respectively. Stability of lignin peroxidase was determined at 37, 45, and 60 degrees C, and over the pH range 4-9.

Enzyme Repression↗
PubMed1981

Arginine regulation of gramicidin S biosynthesis.

Several amino acids are known to affect the gramicidin S producer Bacillus brevis ATCC 9999 with respect ot growth, soluble gramicidin S synthetase formation, antibiotic production, or a combination of these. Our studies confirmed that arginine has paradoxical effects on the B. brevis fermentation; it markedly increased growth and antibiotic production, yet decreased the soluble heavy gramicidin S synthetase activity. We found that arginine did not repress heavy gramicidin S synthetase. The amino acid stimulated growth and increased specific antibiotic production presumably by supplying a limiting precursor (ornithine) for gramicidin S synthesis. Although the amino acid decreased the specific activity of the soluble heavy gramicidin S synthetase, it markedly increased the particulate enzyme activity which persisted hours after the soluble heavy gramicidin S synthetase disappeared. One percent arginine was the optimum level for growth and gramicidin S production. After growth in 1% arginine, heavy synthetase activity in the particulate fraction more than doubled. We propose that arginine leads to the soluble enzyme becoming membrane bound and more stable in vivo. Although we found arginine capable of inhibiting the action of soluble heavy gramicidin S synthetase, this was not the mechanism involved in the lowering of soluble heavy gramicidin S synthetase specific activity.

Amino Acid Isomerases↗
PubMed1980

Novel mutant of Anabaena sp. strain CA which growns on N2 but not on combined nitrogen.

A mutant has been isolated from Anabaena sp. strain CA by treatment with N-methyl-N'-nitro-N-nitrosoguanidine, which has the unusual phenotypic characteristic of growth only under N2-fixing conditions. Growth of the mutant was completely inhibited by NO3- or NH4+ at concentrations routinely used for growth of the wild type, and sensitivity to NH4+ was especially pronounced. The inhibitory effect of NH4+ could not be overcome by glutamine, glutamate, or casein hydrolysate. Ammonia had no immediate inhibitory effect on protein synthesis, CO2 fixation, or O2 evolution, and the gradual inhibition of C2H2 reduction activity by NH4+ resembled a repression phenomenon. The glutamine synthetase activity of N2-fixing cultures appeared normal, yet the mutant was incapable of utilizing exogenous NH4+ for growth. Preliminary evidence suggests a possible alteration of glutamine synthetase, which could result in sensitivity to exogenous NH4+ by progressive inactivation of the enzyme or repression of its synthesis.

Amino Acids↗
PubMed1968

Regulation of nitrogen fixation in Azotobacter vinelandii OP and in an apparently partially constitutive mutant.

Methylamine and 2-methylalanine appeared to act as co-repressors of nitrogenase in Azotobacter vinelandii OP. They inhibited the growth of this organism on molecular nitrogen but not on nitrate, ammonia, or Casamino Acids; they prevented the formation of nitrogenase by cells transferred from repression to induction conditions; and they did not inhibit the activity of nitrogenase in vitro. A mutant of strain OP, selected on the basis of its relative resistance to methylalanine, appeared partially constitutive because nitrogenase in this strain was less sensitive to repressors than was the enzyme in the wild-type strain.

Alanine↗
PubMed1998

Transcriptional co-regulation of Saccharomyces cerevisiae alcohol acetyltransferase gene, ATF1 and delta-9 fatty acid desaturase gene, OLE1 by unsaturated fatty acids.

The ATF1 gene encodes an alcohol acetyl transferase which catalyzes the synthesis of acetate esters from acetyl CoA and several kinds of alcohols. ATF1 expression is repressed by unsaturated fatty acids or oxygen. Analysis using ATF1-lacZ fusion plasmid revealed that ATF1 gene expression is widely repressed by a variety of unsaturated fatty acids, and the degree of ATF1 transcriptional repression varies according to the structure of the unsaturated fatty acids. Interestingly, it was noted that the degree of ATF1 transcriptional repression was related to the melting point of unsaturated fatty acids added to the medium. The OLE1 gene, which encodes delta-9 fatty acid desaturase, has been reported to be repressed by unsaturated fatty acids. Transcription of OLE1 was also repressed by a wide variety of unsaturated fatty acids under anaerobic conditions. The degree of transcriptional repression of OLE1 was also related to the melting point of the added unsaturated fatty acids. Therefore, it is considered that ATF1 and OLE1 transcription are regulated in response to cell membrane fluidity. As has been reported for OLE1, the repression of ATF1 by unsaturated fatty acids was relieved in a disruptant carrying a faa1 and faa4 double mutation, two fatty acid activation genes. However, the ATF1 transcript in this double gene disruptant was repressed by oxygen. These results suggested that ATF1 transcription was co-regulated by the same mechanism as the OLE1 gene and that unsaturated fatty acids and oxygen repressed the ATF1 transcript by a different regulation pathway.

Acetyltransferases↗
PubMed1982

The effect of gyrase inhibitors and cyclic AMP on induction and glucose repression of the 6-hydroxy-nicotine oxidases in Arthrobacter oxidans.

The induction by D,L-nicotine of the enantiozymes 6-hydroxy-L-nicotine oxidase and 6-hydroxy-D-nicotine oxidase in Arthrobacter oxidans was differently affected by the inhibitors of Escherichia coli gyrase, novobiocin and nalidixic acid. These compounds inhibited 6-hydroxy-L-nicotine oxidase induction slightly, but led to an increase in the level of 6-hydroxy-D-nicotine oxidase activity. Furthermore, the specific repression by glucose of 6-hydroxy-D-nicotine oxidase synthesis was not abolished by the addition of cAMP but by that of novobiocin.

Arthrobacter↗
PubMed1976

Evidence that acyl coenzyme A synthetase activity is required for repression of yeast acetyl coenzyme A carboxylase by exogenous fatty acids.

The cellular content of acetyl-CoA carboxylase [acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] in Saccharomyces cerevisiae is reduced by the addition of long-chain fatty acids to the culture medium. Mutant strains of S. cerevisiae defective in acyl-CoA synthetase [acid:CoA ligase (AMP-forming), EC 6.2.1.3] were isolated and used to determine whether fatty acid itself or a metabolite of fatty acid is more directly responsible for the repression of acetyl-CoA carboxylase. Cells of the mutant strains were capable of incorporating fatty acid to an extent comparable to that observed with the wild-type strain, but they accumulated markedly more of the incorporated fatty acid in the nonesterified form than did the wild-type cells. The level of acetyl-CoA carboxylase activity in the mutants, in contrast to that in the wild-type strain, was hardly affected by the addition of fatty acids to the medium. These results indicate that the activation of exogenous fatty acid is required for the repression of acetyl-CoA carboxylase, supporting the view that the repressive effect is mediated by some compound metabolically derived from fatty acid.

Acetate-CoA Ligase↗
PubMed2006

Repression of human GSTA1 by interleukin-1beta is mediated by variant hepatic nuclear factor-1C.

Down-regulation of glutathione transferase A1 (GSTA1) expression has profound implications in cytoprotection against toxic by-products of lipid peroxidation produced during inflammation. We investigated the role of hepatic nuclear factor 1 (HNF-1) in repression of human GSTA1 expression by interleukin (IL)-1beta in Caco-2 cells. In luciferase reporter assays, overexpression of HNF-1alpha increased GSTA1 transcriptional activity via an HNF-1 response element (HRE) in the proximal promoter. In addition, constitutive mRNA levels of GSTA1 and HNF-1alpha rose concurrently in Caco-2 cells with increasing stage of confluence. IL-1beta reduced GSTA1 mRNA levels at all stages of confluence; however, HNF-1alpha mRNA levels were not altered. IL-1beta repressed GSTA1 transcriptional activity, an effect that was abolished by mutating the HRE. Similar results were observed in HT-29 and HepG2 cells. Overexpression of HNF-1alpha did not counteract IL-1beta-mediated repression of GSTA1 transcription either in reporter assays or at the mRNA level. Involvement of the transdominant repressor C isoform of variant HNF-1 (vHNF-1C) in GSTA1 repression was demonstrated, because vHNF-1C overexpression significantly reduced GSTA1 transcriptional activity. Finally, IL-1beta caused concentration-related up-regulation of vHNF-1C mRNA levels and increased binding of vHNF-1C protein to the HRE, whereas HNF-1alpha-HRE complex formation was reduced. These findings indicate that IL-1beta represses GSTA1 transcription via a mechanism involving overexpression of vHNF-1C.

Base Sequence↗
PubMed1981

Cyclic adenosine 3',5'-monophosphate levels in Pseudomonas putida and Pseudomonas aeruginosa during induction and carbon catabolite repression of histidase synthesis.

Inducibility of histidase (histidine ammonia-lyase, EC 4.3.1.3) in Pseudomonas putida and Pseudomonas aeruginosa was observed to be strongly affected by succinate-provoked catabolite repression, but this did not occur as a consequence of reduced intracellular cyclic adenosine 3',5'-monophosphate levels, and repression could not be alleviated by exogenously added cyclic adenosine 3,'5'-monophosphate. Milder repression of histidase by lactate was also not reversed by the addition of cyclic adenosine 3',5'-monophosphate. These results, along with data showing intracellular cyclic adenosine 3',5'-monophosphate levels remained essentially constant during growth on such diverse carbon sources as histidine, acetamide, glucose, and succinate, indicated that catabolite repression of histidase synthesis by efficient carbon sources was not mediated through variations in internal cyclic adenosine 3,'5'-monophosphate.

Ammonia-Lyases↗
PubMed1983

Role of alanine-valine transaminase in Salmonella typhimurium and analysis of an avtA::Tn5 mutant.

In Salmonella typhimurium, as in Escherichia coli, mutations in avtA, the gene encoding the alanine-valine transaminase (transaminase C), are silent unless they are combined with mutations involved in isoleucine-valine biosynthesis. avtA is repressed by leucine or alanine but not by valine. Transaminase C is found at reduced levels upon starvation for any one of several amino acids. We hypothesize that this is due to repression of avtA by the elevated alanine and leucine pools found in amino acid-starved cells.

Culture Media↗
PubMed1987

Molybdenum effector of fumarate reductase repression and nitrate reductase induction in Escherichia coli.

In Escherichia coli the presence of nitrate prevents the utilization of fumarate as an anaerobic electron acceptor. The induction of the narC operon encoding the nitrate reductase is coupled to the repression of the frd operon encoding the fumarate reductase. This coupling is mediated by nitrate as an effector and the narL product as the regulatory protein (S. Iuchi and E. C. C. Lin, Proc. Natl. Acad. Sci. USA 84:3901-3905, 1987). The protein-ligand complex appears to control narC positively but frd negatively. In the present study we found that a molybdenum coeffector acted synergistically with nitrate in the regulation of frd and narC. In chlD mutants believed to be impaired in molybdate transport (or processing), full repression of phi(frd-lac) and full induction of phi(narC-lac) by nitrate did not occur unless the growth medium was directly supplemented with molybdate (1 microM). This requirement was not clearly manifested in wild-type cells, apparently because it was met by the trace quantities of molybdate present as a contaminant in the mineral medium. In chlB mutants, which are known to accumulate the Mo cofactor because of its failure to be inserted as a prosthetic group into proteins such as nitrate reductase, nitrate repression of frd and induction of narC were also intensified by molybdate supplementation. In this case a deficiency of the molybdenum coeffector might have resulted from enhanced feedback inhibition of molybdate transport (or processing) by the elevated level of the unutilized Mo cofactor. In addition, mutations in chlE, which are known to block the synthesis of the organic moiety of the Mo cofactor, lowered the threshold concentration of nitrate (< 1 micromole) necessary for frd repression and narC induction. These changes could be explained simply by the higher intracellular nitrate attainable in cells lacking the ability to destroy the effector.

Chlorates↗
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↗