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At least 955 records · Page 53Linked to original sources
PubMed1978

Kinetics of glucose repression of yeast cytochrome c.

The kinetics of glucose repression of cytochrome c synthesis was measured by a radioimmune assay. When 5 or 10% glucose was added to a derepressed culture, the rate of cytochrome c synthesis was reduced to the repressed level with a half-life of 2 min. The addition of 1 or 0.5% glucose repressed the rate of cytochrome c synthesis to the same level as high glucose concentrations but with a longer half-life of 3 min. Glucose repression had no effect on the stability or function of the cytochrome c protein. Cellular levels of active cytochrome c mRNA during glucose repression were measured by translation of total cellular polyadenylic acid-containing RNA and immunoprecipitation cytochrome c from the translation products. The results of these measurements indicate that glucose represses the rate of cytochrome c synthesis through a reduction in the level of translatable cytochrome c mRNA.

Cytochrome c Group↗
PubMed1984

Repression of nitrogen fixation in Klebsiella pneumoniae at high temperature.

The effect of elevated growth temperature on nif mRNA synthesis, nif protein synthesis, and nitrogenase activity was investigated in wild-type and NifL- strains of Klebsiella pneumoniae. Nitrogenase activity is not affected at 41 degrees C; however, nitrogenase is not synthesized at that temperature. Transcription of three nif operons studied is repressed at 41 degrees C. We show that the nifL protein is not required for repression by high temperature and propose that repression of nif at 41 degrees C results from a reversible inactivation of the nifA gene product.

Acetylene↗
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↗
PubMed1992

Role of the MetR regulatory system in vitamin B12-mediated repression of the Salmonella typhimurium metE gene.

The vitamin B12 (B12)-mediated repression of the metE gene in Escherichia coli and Salmonella typhimurium requires the B12-dependent transmethylase, the metH gene product. It has been proposed that the MetH-B12 holoenzyme complex is involved directly in the repression mechanism. Using Escherichia coli strains lysogenized with a lambda phage carrying a metE-lacZ gene fusion, we examined B12-mediated repression of the metE-lacZ gene fusion. Although B12 supplementation results in a 10-fold repression of metE-lacZ expression, homocysteine addition to the growth medium overrides the B12-mediated repression. In addition, B12-mediated repression of the metE-lacZ fusion is dependent on a functional MetR protein. When a metB mutant was transformed with a high-copy-number plasmid carrying the metE gene, which would be expected to reduce intracellular levels of homocysteine, metE-lacZ expression was reduced and B12 supplementation had no further effect. In a metJ mutant, B12 represses metE-lacZ expression less than twofold. When the metJ mutant was transformed with a high-copy-number plasmid carrying the metH gene, which would be expected to reduce intracellular levels of homocysteine, B12 repression of the metE-lacZ fusion was partially restored. The results indicate that B12-mediated repression of the metE gene is primarily a loss of MetR-mediated activation due to depletion of the coactivator homocysteine, rather than a direct repression by the MetH-B12 holoenzyme.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1994

Glucose kinase has a regulatory role in carbon catabolite repression in Streptomyces coelicolor.

A glucose kinase (glkA) mutant of Streptomyces coelicolor A3(2) M145 was selected by the ability to grow in the presence of the nonmetabolizable glucose analog 2-deoxyglucose. In this glkA mutant, carbon catabolite repression of glycerol kinase and agarase was relieved on several carbon sources tested, even though most of these carbon sources are not metabolized via glucose kinase. This suggests that catabolite repression is not regulated by the flux through glucose kinase and that the protein itself has a regulatory role in carbon catabolite repression. A 10-fold overproduction of glucose kinase also results in relief of catabolite repression, suggesting that excess glucose kinase can titrate the repressing signal away. This could be achieved directly by competition of excess glucose kinase with its repressing form for binding sites on DNA promoter regions or indirectly by competition for binding of another regulatory protein.

Base Sequence↗
PubMed2004

Real-time PCR analysis of carbon catabolite repression of cellobiose dehydrogenase gene transcription in Trametes versicolor.

Cellobiose dehydrogenase production in Trametes versicolor is repressed when additional carbon sources, such as glucose, maltose, galactose, arabinose, and xylose, are added to the fungal cultures growing on cellulose. Real-time quantitative reverse transcription-polymerase chain reaction has been used to demonstrate that the addition of galactose, arabinose, and xylose results in 19-, 92-, and 114-fold reductions, respectively, in cdh transcript levels 96 h post-addition. Glucose exhibits the greatest repressive effect, resulting in a 3400-fold decrease in cdh transcript levels.

Arabinose↗
PubMed2000

Inhibition of TNF-alpha-induced neutrophil apoptosis by crystals of calcium pyrophosphate dihydrate is mediated by the extracellular signal-regulated kinase and phosphatidylinositol 3-kinase/Akt pathways up-stream of caspase 3.

The role of protein kinases in the inhibition of TNF-alpha associated apoptosis of human neutrophils by crystals of calcium pyrophosphate dihydrate (CPPD) (25 mg/ml) was investigated. We monitored the activities of the p44 extracellular signal-regulated kinase 1 (ERK1) and p42 ERK2 mitogen-activated protein (MAP) kinases and phosphatidylinositol 3-kinase (PI3-K)-regulated protein kinase B (Akt) in neutrophils incubated with TNF-alpha and CPPD crystals, separately and in combination, in parallel with the endogenous caspase 3 activity and DNA fragmentation. CPPD crystals were observed to induce a robust and transient activation of ERK1, ERK2, and Akt, whereas TNF-alpha produced only a modest and delayed activation of Akt. In the presence of TNF-alpha, Akt activity was enhanced, and CPPD crystal-induced activation of ERK1 and ERK2 was more sustained than with CPPD crystals alone, but TNF-alpha itself reduced the basal phosphotransferase activities of these MAP kinases. Preincubation with the MAP kinase kinase (MEK1) inhibitors PD98059 (20 ng/ml) and U0126 (250 nM), or the PI3-K inhibitors wortmannin (100 nM) and LY294002 (50 microM) repressed the activation of ERK1, ERK2, and Akt in association with CPPD crystal incubation, in the absence or presence of TNF-alpha. Furthermore, the inhibition of the Mek1/Mek2-->ERK1/ERK2 or PI3-K/Akt pathways reversed CPPD crystal-associated suppression of TNF-alpha-induced caspase 3 activation and neutrophil apoptosis. Together, these results indicate that CPPD crystals function to induce acute inflammatory responses through ERK1/ERK2 and PI3-K/Akt-mediated stimulation of neutrophil activation and repression of apoptosis.

Apoptosis↗
PubMed1990

A glucose-repressible gene encodes acetyl-CoA hydrolase from Saccharomyces cerevisiae.

Acetyl-CoA hydrolase, catalyzing the hydrolysis of acetyl-CoA, is presumably involved in regulating the intracellular acetyl-CoA pool. Recently, a yeast acetyl-CoA hydrolase was purified to homogeneity from Saccharomyces cerevisiae and partially characterized (Lee, F.-J. S., Lin, L.-W., and Smith, J. A. (1989) Eur. J. Biochem. 184, 21-28). In order to study the biological function and regulation of the acetyl-CoA hydrolase, we cloned and sequenced the full length cDNA encoding yeast acetyl-CoA hydrolase. RNA blot analysis indicates that acetyl-CoA hydrolase is encoded by a 2.5-kilobase mRNA. DNA blot analyses of genomic and chromosomal DNA reveal that the gene (so-called ACH1, acetyl-CoA hydrolase) is present as a single copy located on chromosome II. Acetyl-CoA hydrolase is established to be a mannose-containing glycoprotein, which binds concanavalin A. By measuring the levels of ACH1 mRNA and acetyl-CoA hydrolase activity in different growth phases and by examining the effects of various carbon sources, we have demonstrated that ACH1 expression is repressed by glucose.

Acetyl-CoA Hydrolase↗
PubMed1981

Regulation of catalase biosynthesis in Saccharomyces cerevisiae: factor repressing catalase biosynthesis.

A factor which represses the catalase biosynthesis in yeast has been demonstrated in Saccharomyces cerevisiae. This factor can be obtained from yeast cells having both low and normal catalase levels, and is unable to enter the intact cytoplasmic membrane. Moreover, the factor-containing cell extracts obtained either from acatalasemic mutants or normal strains grown in catalase repressive conditions showed higher activity than those obtained from normal strains after being cultured in permissive conditions.

Catalase↗
PubMed1994

The Aspergillus nidulans CREA protein mediates glucose repression of the ethanol regulon at various levels through competition with the ALCR-specific transactivator.

Carbon catabolite repression in Aspergillus nidulans is mediated by a negative-acting protein coded by the creA gene. We have investigated how CREA controls the expression of the ethanol regulon genes. CREA is a major component of the control of this regulon. Its presence in the cell results in a permanent, albeit partial, repression of the alc genes under all physiological growth conditions, even when the fungus is grown on carbon sources considered to be non-repressing. A crucial step in the control processes is the repression of the positive-acting specific regulatory gene alcR, by the binding of CREA on its cognate target sites on the alcR promoter. The removal of one of these targets, URSA, results in a 50% derepression of the alcR gene. Furthermore, the presence of this sequence contributes directly to the low alcR expression under nonrepressing conditions and reduces alcR promoter function by at least 100-fold. CREA acts both on the regulatory gene alcR and directly on the two structural genes alcA and aldA, as glucose repression of the latter genes occurs in strains where alcR transcription is driven by a strong constitutive and derepressed promoter. In vivo and in vitro competition experiments show that CREA acts by competing directly with the binding of the ALCR activator for the same region of the alcR promoter, a region which encompasses overlapping targets for both regulatory proteins. These data are consistent with a model in which the activating and repressing regulatory proteins compete to regulate expression of the ethanol regulon genes.

Alcohol Dehydrogenase↗
PubMed2000

Regulation of endopolygalacturonase gene expression in Botrytis cinerea by galacturonic acid, ambient pH and carbon catabolite repression.

The phytopathogenic fungus Botrytis cinerea produces a set of endopolygalacturonases (endoPGs) which are involved in the enzymatic degradation of pectin in plant cell walls. The endoPG-encoding genes of B. cinerea are differentially expressed when the fungus is grown in liquid culture on different carbon sources. A basic constitutive expression level was observed for two genes, Bcpg1 and Bcpg2, which encode basic isozymes. Galacturonic acid was shown to induce the expression of Bcpg4 and Bcpg6. Low pH of the culture medium resulted in induced expression of the Bcpg3 gene. Expression of the Bcpg5 gene was inducible; however the inducing factors could not be identified. Finally, galacturonic acid-induced expression of the Bcpg4 gene was repressed by the presence of more-favourable carbon sources, such as glucose.

Arabinose↗
PubMed1999

Glucose repression of the Kluyveromyces lactis invertase gene KlINV1 does not require Mig1p.

Kluyveromyces lactis, a budding yeast related to Saccharomyces cerevisiae, can grow on a wider variety of substrates and shows less sensitivity to glucose repression than does Saccharomyces cerevisiae. Many genes that are subject to glucose repression in S. cerevisiae are repressed only weakly or not at all in K. lactis. The molecular basis for this difference is largely unknown. To compare the mechanisms that regulate glucose repression in K. lactis and S. cerevisiae, we decided to clone and analyse an invertase gene from K. lactis. The SUC2 gene, which encodes invertase in S. cerevisiae, is strongly regulated by glucose and serves as a model system for studies on glucose repression. The invertase gene of K. lactis, KlINV1, was isolated by colony hybridization using a conserved region within the inulinase gene of K. marxianus as a probe. Two independent clones obtained were shown to contain the same ORF of 1827 bp. The deduced amino acid sequence is 59% similar to that of the K. marxianus inulinase and shows 49% similarity to ScSuc2p. Gene disruption experiments and low-stringency Southern analysis indicate that KlINV1 is a unique gene in K. lactis. Northern analysis revealed that the transcription of KlINV1 is strongly repressed in the presence of glucose, but, in contrast to the case in S. cerevisiae, repression is independent of KlMig1p.

Amino Acid Sequence↗
PubMed1976

Amino acids as repressors of nitrogenase biosynthesis in Klebsiella pneumoniae.

Nitrogenase biosynthesis in Klebsiella pneumoniae including mutant strains, which produce nitrogenase in the presence of NH+4 (Shanmugam, K.T., Chan, Irene, and Morandi, C. (1975) Biochim. Biophys. Acta 408, 101--111) is repressed by a mixture of L-amino acids. Biochemical analysis shows that glutamine synthetase activity in strains SK-24, SK-28, and SK-29 is also repressed by amino acids, with no detectable effect on glutamate dehydrogenase. Among the various amino acids, L-glutamine in combination with L-aspartate was found to repress nitrogenase biosynthesis completely. In the presence of high concentrations of glutamine (1 mg/ml) even NH+4 repressed nitrogenase biosynthesis in the strains SK-27, SK-37, SK-55 and SK-56. Under these conditions, increased glutamate dehydrogenase activity was also detected. Physiological studies show that nitrogenase derepressed strains are unable to utilize NH+4 as sole source of nitrogen for biosynthesis of glutamate for biosynthesis of glutamate, whereas back mutations leading to NH+4 utilization results in sensitivity to repression by NH+4. These findings suggest that amino acids play an important role as regulators of nitrogen fixation.

Amino Acids↗
PubMed1995

Regulation of expression of the valine (branched-chain amino acid) dehydrogenase-encoding gene from Streptomyces coelicolor.

Expression of the Streptomyces coelicolor (Sc) valine (branched-chain amino acid) dehydrogenase-encoding gene (vdh) is regulated by valine, glucose and NH+4 at the transcriptional level. The results of assays for the level of accumulated vdh mRNA in the Sc J802 strain by primer extension experiments and for the level of catechol dioxygenase (XylE) activity in Sc J802 (vdh::xylE) transformants show that transcription of the vdh gene is induced approx. 2.5-fold by valine, as compared to asparagine as the sole nitrogen source in the presence of glucose as carbon source. Valine induction is repressed by glucose, as compared to glycerol as the carbon source, and by NH+4. Glucose catabolite repression is relieved in Sc M480, a glucose kinase (glkA) deletion mutant. This suggests that glucose repression of vdh and carbohydrate metabolism are due to the same mechanism in Sc, which involves glucose kinase.

Amino Acid Oxidoreductases↗