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At least 1,135 records · Page 63Linked to original sources
PubMed1999

rsmC of the soft-rotting bacterium Erwinia carotovora subsp. carotovora negatively controls extracellular enzyme and harpin(Ecc) production and virulence by modulating levels of regulatory RNA (rsmB) and RNA-binding protein (RsmA).

Previous studies have shown that the production of extracellular enzymes (pectate lyase [Pel], polygalacturonase [Peh], cellulase [Cel], and protease [Prt]) and harpin(Ecc) (the elicitor of hypersensitive reaction) in Erwinia carotovora subsp. carotovora is regulated by RsmA, an RNA-binding protein, and rsmB, a regulatory RNA (Rsm stands for regulator of secondary metabolites) (Y. Liu et al., Mol. Microbiol. 29:219-234, 1998). We have cloned and characterized a novel regulatory gene, rsmC, that activates RsmA production and represses extracellular enzyme and harpin(Ecc) production, rsmB transcription, and virulence in E. carotovora subsp. carotovora. In an rsmC knockout mutant of E. carotovora subsp. carotovora Ecc71 carrying the chromosomal copy of the wild-type rsmA(+) allele, the basal levels of Pel, Peh, Cel, Prt, and harpin(Ecc) as well as the amounts of rsmB, pel-1, peh-1, celV, and hrpN(Ecc) transcripts are high, whereas the levels of rsmA transcripts and RsmA protein are low. Furthermore, the expression of an rsmA-lacZ gene fusion is lower in the RsmC(-) mutant than in the RsmC(+) parent. Conversely, the expression of an rsmB-lacZ operon fusion is higher in the RsmC(-) mutant than in the RsmC(+) parent. These observations establish that RsmC negatively regulates rsmB transcription but positively affects RsmA production. Indeed, comparative studies with an RsmC(-) mutant, an RsmA(-) mutant, and an RsmA(-) RsmC(-) double mutant have revealed that the negative effects on exoprotein production and virulence are due to the cumulative regulatory effects of RsmC on rsmA and rsmB. Exoprotein production by the RsmC(-) mutant is partially dependent on the quorum sensing signal, N-(3-oxohexanoyl)-L-homoserine lactone. Southern blot data and analysis of PCR products disclosed the presence of rsmC sequences in E. carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, and E. carotovora subsp. carotovora. These findings collectively support the idea that rsmA and rsmB expression in these plant pathogenic Erwinia species is controlled by RsmC or a functional homolog of RsmC.

Amino Acid Sequence↗
PubMed1992

The metabolism of gluconate in Escherichia coli: a study in continuous culture.

The gluconate metabolism in Escherichia coli involves duplicate activities of transport and phosphorylation for gluconate. In both cases, these activities can be differentiated in vitro by their different affinities for the substrate. In addition, the two gluconokinases can be differentiated by their heat sensitivities. The technique of continuous culture was used to investigate the influence of the growth rate on this metabolism in an E. coli HfrG6 strain during gluconate-limited growth under conditions of high and low oxygen concentrations. The transport and phosphorylation for gluconate, induced when the cells are cultivated in media with gluconate were differently influenced by the culture dilution rate. These activities were induced under the two conditions investigated; however, the low affinity transport system for gluconate and the thermosensitive gluconokinase were not detected under conditions of high and low oxygen concentrations, respectively. The induction of the dehydratase was favoured under conditions of low oxygen concentration. The experimental data suggest that induction and repression work together to regulate the levels of these activities during gluconate-limited growth conditions. Furthermore, that an effector molecule distinct from gluconate might be involved in the induction of the dehydratase.

Bacteriological Techniques↗
PubMed1980

The Escherichia coli L-arabinose operon: binding sites of the regulatory proteins and a mechanism of positive and negative regulation.

The locations of DNA binding by the proteins involved with positive and negative regulation of transcription initiation of the L-arabinose operon in Escherichia coli have been determined by the DNase I protection method. Two cyclic AMP receptor protein sites were found, at positions -78 to -107 and -121 to -146, an araC protein--arabinose binding site was found at position -40 to -78, and an araC protein-fucose binding site was found at position -106 to -144. These locations, combined with in vivo data on induction of the two divergently oriented arabinose promoters, suggest the following regulatory mechanism: induction of the araBAD operon occurs when cyclic AMP receptor protein, araC protein, and RNA polymerase are all present and able to bind to DNA. Negative regulation is accomplished by the repressing form of araC protein binding to a site in the regulatory region such that it stimultaneously blocks access of cyclic AMP receptor protein to two sites on the DNA, one site of which serves each of the two promoters. Thus, from a single operator site, the negative regulator represses the two outwardly oriented ara promoters. This regulatory mechanism explains the known positive and negative regulatory properties of the ara promoters.

AraC Transcription Factor↗
PubMed1993

Mutations that relieve nutritional repression of the Bacillus subtilis dipeptide permease operon.

The Bacillus subtilis dciA operon encodes a dipeptide transport complex that is induced rapidly as cells enter stationary phase and initiate sporulation. Expression of this operon in growing cells is repressed by glucose, by a mixture of amino acids, and by the AbrB protein. A genetic screen was devised to identify mutations that allow inappropriate expression from the dciA promoter during growth. These mutations resulted in increased dciA transcription during growth in nutrient broth, in minimal amino acids medium, and in minimal glucose medium. Some of the mutations, called dcs (dciA control site), were cloned and shown by sequence analysis to cluster near the start site of dciA transcription. Primer extension and in vitro transcription analysis revealed that the dcs mutations did not create a new promoter. These mutations may therefore disrupt an operator site necessary for the binding of a negative regulator responsive to the nutritional state of the cell. The dcs mutant promoters were still subject to AbrB control, suggesting that the dciA operon is regulated by at least two proteins, AbrB and a nutritionally responsive regulator. The gene(s) for the putative nutritional regulator may be defined by the cod (control of dciA) mutations, which appeared to relieve amino acid and glucose repression of dciA by altering a diffusible factor. An abrB cod double mutant exhibited high-level expression of dciA during exponential growth phase.

Amino Acids↗
PubMed1996

Genetic analysis of the dsz promoter and associated regulatory regions of Rhodococcus erythropolis IGTS8.

The dsz gene cluster of Rhodococcus erythropolis IGTS8 comprises three genes, dszA, dszB, and dszC, whose products are involved in the conversion of dibenzothiophene (DBT) to 2-hydroxybiphenyl and sulfite. This organism can use DBT as the sole sulfur source but not as a carbon source. Dsz activity is repressed by methionine, cysteine, Casamino Acids, and sulfate but not by DBT or dimethyl sulfoxide. We cloned 385 bp of the DNA immediately 5' to dszA in front of the reporter gene lacZ of Escherichia coli. We showed that this region contains a Rhodococcus promoter and at least three dsz regulatory regions. After hydrazine mutagenesis of this DNA, colonies that were able to express beta-galactosidase in the presence of Casamino Acids were isolated. Sequencing of these mutants revealed two possible regulatory regions. One is at -263 to -244, and the other is at -93 to -38, where -1 is the base preceding the A of the initiation codon ATG of dszA. An S1 nuclease protection assay showed that the start of the dsz promoter is the G at -46 and that transcription is repressed by sulfate and cysteine but not by dimethyl sulfoxide. The promoter encompasses a region of potential diad symmetry that may contain an operator. Immediately upstream of the promoter is a protein-binding domain between -146 and -121. Deletion of this region did not affect repression, but promoter activity appeared to be reduced by threefold. Thus, it could be an activator binding site or an enhancer region.

Bacterial Proteins↗
PubMed1998

Repression of basal transcription by vitamin D receptor: evidence for interaction of unliganded vitamin D receptor with two receptor interaction domains in RIP13delta1.

Repression of basal transcription of a 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) responsive 25-hydroxyvitamin D3-24-hydroxylase (CYP24) promoter construct as observed in kidney cells in the absence of ligand and this repression was dependent on a functional vitamin D response element (VDRE). Basal repression was also seen with a construct where a consensus DR-3-type VDRE was fused to the thymidine kinase promoter. Expression of a dominant negative vitamin D receptor (VDR) isoform that strongly bound to the VDRE motif in the CYP24 promoter ablated basal repression. This VDR isoform lacked sequence in the hinge- and ligand-binding domains implicating one or both of these domains in basal repression. It is well known that thyroid hormone and retinoic acid receptors silence basal transcription of target genes in the absence of ligands and this repressor function can be mediated by the nuclear receptor corepressor N-CoR. Two variants of N-CoR have been described, RIP13a and RIP13delta1. N-CoR and the variants contain two receptor interaction domains, ID-I and ID-II, which are identical except region ID-II in RIP13delta1 has an internal deletion. We have used the mammalian two hybrid system to investigate whether VDR, in the absence of ligand 1,25-(OH)2D3, can interact with these domains. The data showed that unliganded VDR does not interact with either ID-I or ID-II from RIP13a and RIP13delta1, but does interact strongly with a composite domain of ID-I and ID-II from RIP13delta1 (but not from RIP13a) and this strong interaction is abrogated in the presence of ligand. This finding implicates RIP13delta1 in VDR-dependent basal repression of the promoter constructs under investigation. However, over-expression of RIP13delta1 in kidney cell lines did not alter basal expression of the CYP24 promoter construct. It is concluded that either the level of endogenous RIP13delta1 in these kidney cells permits maximal repression or that repression occurs by a mechanism that is independent of RIP13delta1. Alternatively, repression may be dependent on RIP13delta1 but requires an additional cofactor that is limiting in these cells.

Animals↗
PubMed1975

Tryptophanase of fecal flora as a possible factor in the etiology of colon cancer.

Twenty-three strains of intestinal anaerobes obtained from two laboratories were examined for indole production from tryptophan. Among the 23 isolates tested, three of Bacteroides fragilis thetaiotaomicron and one Citrobacter sp. were indole positive. The tryptophanase of the indole-positive strains of intestinal anaerobes was inducible by tryptophan and was susceptible to glucose repression. The products of tryptophanase activity were formed in stoichiometric amounts by dialyzed, freshly prepared extracts. The tryptophan concentration and tryptophanase activity in feces from rats on an all-meat diet were significantly higher than those in feces from rats on a normal diet. The results indicated that the higher tryptophanase activity in the feces of rats fed an all-meat diet is due to the inducibility of this enzyme by tryptophan and is not due to any inhibitor in the feces of rats on a normal diet. The results also suggested that a population with a diet rich in meat has a greater chance for exposure to possible carcinogens such as indole and other tryptophan metabolites. This agrees with the hypothesis, based on epidemiologic data, that a high intake of meat may be related to the development of colon cancer in man.

Bacteroides↗
PubMed1978

Cellulose degradation and cellulase formation by Phialophora malorum.

The formation of cellulases and beta-glucosidase and their location in the fungus Phialophora malorum was studied on some different carbon sources. The cellulases were found to be partly cell-free and partly cell-bound during growth on cellulose and carboxymethyl-cellulose. Glucose and cellobiose repressed the cellulase formation but a low carboxymethylcellulase activity was measurable on the glucose-grown mycelium. The unicellular stage did not appear to grow on carboxymethyl-cellulose or cellulose, but mycelium was formed on these carbon sources.

Biodegradation, Environmental↗
PubMed1999

Transcriptional repression of the human collagenase-1 (MMP-1) gene in MDA231 breast cancer cells by all-trans-retinoic acid requires distal regions of the promoter.

In the present study, we investigated the mechanisms controlling constitutive transcription of collagenase-1 and its repression by all-trans-retinoic acid (RA) in the highly invasive metastatic and oestrogen-receptor-negative breast cancer cell line MDA231. A combination of in vivo and in vitro experiments that include DNAase I hypersensitivity assays, transient transfection of collagenase-1 promoter constructs, and electrophoretic mobility shift assays implicate several PEA3 sites, binding sites for Ets-related transcription factors, in the constitutive expression of the human collagenase-1 promoter. Transient transfection of promoter constructs linked to the luciferase reporter, along with gel retardation assays, revealed that repression of collagenase-1 transcription by RA is not dependent on the proximal AP-1 site, but, rather, requires sequences located in distal regions of the promoter. Transcriptional analyses and electrophoretic mobility shift assays suggest that the PEA3 site located at -3108 bp facilitates, at least in part, the transcriptional repression of the human collagenase-1 gene in MDA231 cells. We conclude that collagenase-1 repression in MDA231 cells occurs by a novel regulatory pathway that does not depend on the proximal AP-1 site at -73 bp, but does depend on distal regions in the collagenase-1 promoter.

Collagenases↗
PubMed1978

Physiology of L-asparaginase synthesis in recombinants of Escherichia coli A-1.

A mating between Escherichia coli 4318 (thi leu Las- Hfr) and E. coli A-1 (Met- Las+ F-) resulted in the formation of prototrophic recombinants having L-asparaginase activities at three distinct levels. The physiology of L-asparaginase synthesis in these recombinants is decribed. One class of recombinants produced significantly more L-asparaginase than E. coli A-1. L-Asparaginase synthesis in the recombinants was inhibited by the presence of dissolved oxygen in the medium and was transiently repressed by the presence of glucose in the same manner as that observed in the parental strains. L-Asparaginase activity was increased by the addition of oxalacetate as well as other members of the tricarboxylic acid cycle.

Asparaginase↗
PubMed1974

Derepression of synthesis of the aminoacyl-transfer ribonucleic acid synthetases for the branched-chain amino acids of Escherichia coli.

The kinetics of derepression of valyl-, isoleucyl-, and leucyl-transfer ribonucleic acid (tRNA) synthetase formation was examined during valine-, isoleucine-, and leucine-limited growth. When valine was limiting growth, valyl-tRNA synthetase formation was maximally derepressed within 5 min, whereas the rates of synthesis of isoleucyl-, and leucyl-tRNA synthetases were unchanged. Isoleucine-restricted growth caused a maximal derepression of isoleucyl-tRNA synthetase formation in 5 min and derepression of valyl-tRNA synthetase formation in 15 min with no effect on leucyl-tRNA synthetase formation. When leucine was limiting growth, leucyl-tRNA synthetase formation was immediately derepressed, whereas valyl- and isoleucyl-tRNA synthetase formation was unaffected by manipulation of the leucine supply to the cells. These results support our previous findings that valyl-tRNA synthetase formation is subject to multivalent repression control by both isoleucine and valine. In contrast, repression control of iso-leucyl- and leucyl-tRNA synthetase formation is specifically mediated by the supply of the cognate amino acid.

Amino Acyl-tRNA Synthetases↗
PubMed1975

Transport of D- and L-tryptophan in Bacillus megaterium by an inducible permease.

Tryptophan-grown cells of Bacillus megaterium ATCC 19213 contain a permease system that transports both D- and L-tryptophan and is inhibited by sodium azide. Arginine-grown cells contain little tryptophan permease activity, suggesting that the system is inducible. Arginine represses the tryptophan permease as well as the transport system for leucine and phenylalanine. Kynurenine was a more effective inducer of the tryptophan transport system than either D- or L-tryptophan.

Arginine↗
PubMed1984

Cyclic AMP levels during induction and repression of cellulase biosynthesis in Thermomonospora curvata.

Specific cellulase production rates (SCPR) were compared with intracellular cyclic AMP (cAMP) levels in the thermophilic actinomycete, Thermomonospora curvata, during growth on several carbon sources in a chemically defined medium. SCPR and cAMP levels were 0.03 U (endoglucanase [EG] units) and 2 pmol per mg of dry cells, respectively, during exponential growth on glucose. These values increased to about 6 and 25, respectively, during growth on cellulose. Detectable EG production ceased when cAMP levels dropped below 10. Cellobiose (usually considered to be a cellulase inducer) caused a sharp decrease in cAMP levels and repressed EG production when added to cellulose-grown cultures. 2-deoxy-D-glucose, although nonmetabolizable in T. curvata, depressed cAMP to levels observed with glucose, but unlike glucose, the 2DG effect persisted until cells were washed and transferred to fresh medium. SCPR values and cAMP levels in cells grown in continuous culture under conditions of cellobiose limitation were markedly influenced by dilution rate (D). The maxima for both occurred at D = 0.085 (culture generation time of 11.8 h). When D was held constant and cellobiose concentration was increased over a 14-fold range to support higher steady state population levels, SCPR values decreased about fivefold, indicating that extracellular catabolite accumulation may be a factor in EG repression. The role of cAMP in the mechanism of this repression appears to be neither simple nor direct, since large changes (up to 200-fold) in SCPR accompany relatively small changes (10-fold) in cellular cAMP levels.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1989

Oxysterol regulators of 3-hydroxy-3-methylglutaryl-CoA reductase in liver. Effect of dietary cholesterol.

Hepatic regulatory oxysterols were analyzed to determine which oxysterols were present in livers of mice fed a cholesterol-free diet and whether repression of 3-hydroxy-3-methylglutaryl-CoA reductase following cholesterol feeding was accompanied by an increase in one or more oxysterols. Analysis of free and esterified sterols from mice fed a cholesterol-free diet resulted in the identification and quantitation of six regulatory oxysterols: 24-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol, 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol, and 7-ketocholesterol. Following the addition of cholesterol to the diet for 1 or 2 nights, hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity declined and the levels of oxysterols, especially those of the side-chain-hydroxylated sterols, increased. Total 3-hydroxy-3-methylglutaryl-CoA reductase repressor units attributable to identified free oxysterols increased 2.5- and 6-fold after 1 and 2 nights, respectively, of cholesterol feeding. The amounts of esterified 24-, 25-, and 26-hydroxycholesterol also increased, with the increase in esterified 24-hydroxycholesterol being the greatest. The 24-hydroxycholesterol was predominantly the 24S epimer and the 26-hydroxycholesterol was predominantly the 25R epimer, indicating enzymatic catalysis of their formation. The observed correlation between increased levels of regulatory oxysterols and repression of 3-hydroxy-3-methylglutaryl-CoA reductase in cholesterol-fed mice is consistent with a hypothesis that intracellular oxysterol metabolites regulate the level of the reductase.

Animals↗
PubMed1973

In vitro repression of transcription of the tryptophan operon by trp repressor.

The in vitro repression of transcription of the tryptophan operon by the trp repressor from Escherichia coli was studied. By measuring the inhibitory effect for trp-specific RNA synthesis in an in vitro transcription system directed by DNA of trp-transducing phage, we have detected and concentrated a trp repressor in an eluate of a Phi80 ptED native DNA-cellulose column. The repression of transcription of trp operon required the addition of L-tryptophan in the system, and when several tryptophan analogues were added, the repression or derepression was similar to that observed in vivo. The repressor fraction was separated from the majority of tryptophanyl-tRNA synthetase activity by Bio-gel P60 column chromatography.

Acrylates↗
PubMed1993

MetJ-mediated regulation of the Salmonella typhimurium metE and metR genes occurs through a common operator region.

In Salmonella typhimurium the metE and metR promoters overlap and are divergently transcribed. Three tandem repeats of an 8 bp sequence defined previously as the metE operator site for MetJ-mediated repression also overlap the -35 region of the metR promoter. Starting with a metE-lacZ.metR-galK double gene fusion, site-directed mutagenesis was used to change nucleotides in each of the repeat units from the consensus sequence. Each mutation, along with the wild-type metE-lacZ.metR-galK gene fusion, was cloned into phage lambda gt2. Regulation of the metE and metR genes was examined by measuring beta-galactosidase and galactokinase levels in Escherichia coli strains lysogenized with phage carrying the wild-type and mutant fusions. Mutations in each of the 8 bp repeat units disrupt MetJ-mediated repression for both the metE-lacZ and metR-galK gene fusions, suggesting that the metE and metR genes share a common operator site for the MetJ repressor.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1976

Glutamate dehydrogenase: genetic mapping and isolation of regulatory mutants of Klebsiella aerogenes.

The gene for glutamate dehydrogenase (gdhD) has been mapped in Klebsiella aerogenes by P1 transduction. It is linked to pyrF and trp with the order pyrF-trp-gdh. Complementation analysis using F' episomes from Escherichia coli suggests an analogous location in E. coli. Two mutants able to produce glutamate dehydrogenase in the presence of high levels of glutamine synthetase have been isolated. One, tightly linked to gdhD, shows normal repression control by glutamine synthetase but produces four times as much glutamate dehydrogenase activity as does the wild type under all conditions tested. The other revertant is not linked to gdhD or glnA.

Ammonia↗
PubMed1995

The HPr protein of the phosphotransferase system links induction and catabolite repression of the Bacillus subtilis levanase operon.

The LevR protein is the activator of expression of the levanase operon of Bacillus subtilis. The promoter of this operon is recognized by RNA polymerase containing the sigma 54-like factor sigma L. One domain of the LevR protein is homologous to activators of the NtrC family, and another resembles antiterminator proteins of the BglG family. It has been proposed that the domain which is similar to antiterminators is a target of phosphoenolpyruvate:sugar phosphotransferase system (PTS)-dependent regulation of LevR activity. We show that the LevR protein is not only negatively regulated by the fructose-specific enzyme IIA/B of the phosphotransferase system encoded by the levanase operon (lev-PTS) but also positively controlled by the histidine-containing phosphocarrier protein (HPr) of the PTS. This second type of control of LevR activity depends on phosphoenolpyruvate-dependent phosphorylation of HPr histidine 15, as demonstrated with point mutations in the ptsH gene encoding HPr. In vitro phosphorylation of partially purified LevR was obtained in the presence of phosphoenolpyruvate, enzyme I, and HPr. The dependence of truncated LevR polypeptides on stimulation by HPr indicated that the domain homologous to antiterminators is the target of HPr-dependent regulation of LevR activity. This domain appears to be duplicated in the LevR protein. The first antiterminator-like domain seems to be the target of enzyme I and HPr-dependent phosphorylation and the site of LevR activation, whereas the carboxy-terminal antiterminator-like domain could be the target for negative regulation by the lev-PTS.

Amino Acid Sequence↗