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PubMed1975

Hexamer of bacteriophage f2 coat protein as a repressor of bacteriophage RNA polymerase synthesis.

Formation of complex I between phage f2 RNA and coat protein, leading to repression of phage RNA polymerase synthesis, depends nonlinearly upon the concentration of the coat protein. Maximum formation of complex I was observed when six molecules of coat protein were bound to one molecule of RNA. RNase digestion of a glutaraldehyde-fixed complex left, as the products, coat protein oligomers. The heaviest, hexamers, predominated in the mixture. It was also shown that, in an ionic environment required for phage protein synthesis, coat protein at a concentration optimum for complex I formation exists in solution as a dimer. The results indicate that the translational repression of the RNA polymerase cistron is due to a cooperative attachment to phage template of three dimers of coat protein, forming a hexameric cluster on an RNA strand.

Centrifugation, Density Gradient↗
PubMed1990

Position effect at S. cerevisiae telomeres: reversible repression of Pol II transcription.

S. cerevisiae chromosomes end with the telomeric repeat (TG1-3)n. When any of four Pol II genes was placed immediately adjacent to the telomeric repeats, expression of the gene was reversibly repressed as demonstrated by phenotype and mRNA analyses. For example, cells bearing a telomere-linked copy of ADE2 produced predominantly red colonies (a phenotype characteristic of ade2- cells) containing white sectors (characteristic of ADE2+ cells). Repression was due to proximity to the telomere itself since an 81 bp tract of (TG1-3)n positioned downstream of URA3 when URA3 was approximately 20 kb from the end of chromosome VII did not alter expression of the gene. However, this internal tract of (TG1-3)n could spontaneously become telomeric, in which case expression of the URA3 gene was repressed. These data demonstrate that yeast telomeres exert a position effect on the transcription of nearby genes, an effect that is under epigenetic control.

Chromosome Mapping↗
PubMed1996

Regulation of phosphatase synthesis in Saccharomyces cerevisiae--a review.

Transcription of the genes encoding acid and alkaline phosphatases and the inorganic phosphate (Pi) transporter of Saccharomyces cerevisiae are coordinately repressed and derepressed depending on the Pi concentration in the culture medium. This phosphatase system is particularly suited for the study of regulatory mechanisms, because the acid phosphatase activity of each colony on a plate is easily detected by specific staining methods and there is a 500-fold difference between the repressed and derepressed levels of acid phosphatase activity. With these advantages, considerable amounts of genetic and molecular evidence have been accumulated in the past two decades. This article summarizes our current knowledge on this subject.

Acid Phosphatase↗
PubMed1996

Repression of a matrix metalloprotease gene by E1A correlates with its ability to bind to cell type-specific transcription factor AP-2.

Adenovirus E1A 243-amino acid protein can repress a variety of enhancer -linked viral and cellular promoters. This repression is presumed to be mediated by its interaction with and sequestration of p3OO, a transcriptional coactivator. Type IV 72-kDa collagenase is one of the matrix metalloproteases that has been implicated in differentiation, development, angiogenesis, and tumor metastasis. We show here that the cell type-specific transcription factor AP-2 is an important transcription factor for the activation of the type IV 72-kDa collagenase promoter and that adenovirus E1A 243-amino acid protein represses this promoter by targeting AP-2. Glutathione S-transferase-affinity chromatography studies show that the E1A protein interacts with the DNA binding/dimerization region of AP-2 and that the N-terminal amino acids of E1A protein are required for this interaction. Further, E1A deletion mutants which do not bind to p3OO can repress this collagenase promoter as efficiently as the wildtype E1A protein. Because the AP-2 element is present in a variety of viral and cellular enhancers which are repressed by E1A, these studies suggest that E1A protein can repress cellular and viral promoter/enhancers by forming a complex with cellular transcription factors and that this repression mechanism may be independent of its interaction with p3OO.

Adenovirus E1A Proteins↗
PubMed1973

Rapid regulation of an anthranilate synthase aggregate by hysteresis.

The anthranilate synthase aggregate from Bacillus subtilis is composed of two nonidentical subunits, denoted E and X, which are readily associated or dissociated. A complex of subunit E and X can utilize glutamine or ammonia as substrates in the formation of anthranilate. Partially purified subunit E is capable of using only ammonia as the amide donor in the anthranilate synthase reaction. The stability of the EX complex is strongly influenced by glutamine and by the concentrations of the subunits. Glutamine stabilizes the aggregate as a molecular species in which the velocity of the glutamine-reactive anthranilate synthase is a linear function of protein concentration. In the absence of glutamine the aggregate is readily dissociated following dilution of the extract; that is, velocity concaves upward as a function of increasing protein concentration. Reassociation of the EX complex is characterized by a velocity lag (or hysteretic response) before steady-state velocity for the glutamine-reactive anthranilate synthase is reached. We propose that association and dissociation of the anthranilate synthase aggregate may be physiologically significant and provide a control mechanism whereby repression or derepression causes disproportionate losses or gains in activity by virtue of protein-protein interactions between subunits E and X.

Ammonia↗
PubMed2002

Control of inducer accumulation plays a key role in succinate-mediated catabolite repression in Sinorhizobium meliloti.

The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti favors succinate and related dicarboxylic acids as carbon sources. As a preferred carbon source, succinate can exert catabolite repression upon genes needed for the utilization of many secondary carbon sources, including the alpha-galactosides raffinose and stachyose. We isolated lacR mutants in a genetic screen designed to find S. meliloti mutants that had abnormal succinate-mediated catabolite repression of the melA-agp genes, which are required for the utilization of raffinose and other alpha-galactosides. The loss of catabolite repression in lacR mutants was seen in cells grown in minimal medium containing succinate and raffinose and grown in succinate and lactose. For succinate and lactose, the loss of catabolite repression could be attributed to the constitutive expression of beta-galactoside utilization genes in lacR mutants. However, the inactivation of lacR did not cause the constitutive expression of alpha-galactoside utilization genes but caused the aberrant expression of these genes only when succinate was present. To explain the loss of diauxie in succinate and raffinose, we propose a model in which lacR mutants overproduce beta-galactoside transporters, thereby overwhelming the inducer exclusion mechanisms of succinate-mediated catabolite repression. Thus, some raffinose could be transported by the overproduced beta-galactoside transporters and cause the induction of alpha-galactoside utilization genes in the presence of both succinate and raffinose. This model is supported by the restoration of diauxie in a lacF lacR double mutant (lacF encodes a beta-galactoside transport protein) grown in medium containing succinate and raffinose. Biochemical support for the idea that succinate-mediated repression operates by preventing inducer accumulation also comes from uptake assays, which showed that cells grown in raffinose and exposed to succinate have a decreased rate of raffinose transport compared to control cells not exposed to succinate.

Bacterial Proteins↗
PubMed1984

Glucose represses transcription of Saccharomyces cerevisiae nuclear genes that encode mitochondrial components.

By Northern blot hybridization analysis, we demonstrated that the steady-state levels of mRNAs specifying the alpha subunit of ATPase, the beta subunit of ATPase, and the ATP/ADP translocator are all reduced in cells grown in glucose-rich medium. The extent to which glucose represses the levels of alpha, beta, and translocator mRNAs varies from strain to strain, from 2.5- to 7-fold. Furthermore, by hybridization experiments with an excess of DNA, we showed that glucose represses the rates of synthesis of these mRNAs. The kinetics of repression and depression of transcription were also studied. Finally, a mutant was characterized which appears to be defective in depression of transcription of the genes encoding the alpha and beta ATPase subunits as well as the ATP/ADP translocator.

Adenosine Triphosphatases↗
PubMed1991

[Functional interaction between estrogen receptor and proto-oncogene products c-Jun and c-Fos].

We show here that TPA treatment of MCF-7 cells represses estrogen receptor dependent transcriptional activity, while increasing the AP1 binding activity. These two events are probably linked, since the transcriptional activity of the estrogen receptor in these cells is repressed by overexpression of both cJun or cFos, the components of the AP1 transcripts factor. On the contrary no repression was observed after overexpression of another member of the jun family, the JunD. The repression caused by cJun or cFos may depend on partially different pathways. Our results suggest that the inhibition of TPA of the estrogen dependent growth of the MCF-7 cells is caused by over expression of cJun and cFos.

Drug Interactions↗
PubMed1986

[Development of catabolic repression during Escherichia coli growth on a carbohydrate mixture].

During the cell growth with mixture of three sources of carbon (mannit-arabinose-glycerol, glucose-sorbite-glycerol, glucose-sorbite-galactose) the components of the mixture have been found to be utilized in series. After using up the first, the repression is eliminated unselectively in utilization both the second and the third. Then after the lag-period the utilization repression of the third carbon source by the second one occurs. The phenomenon of "remaining repression" consisting in that at the cell growth with mixture of mannite and sorbite after using up the first carbohydrate the cells cannot start utilizing the second has been described.

Carbohydrate Metabolism↗
PubMed1974

Effect of glucose on the fruiting body formation and adenosine 3',5'-cyclic monophosphate levels in Coprinus macrorhizus.

The formation of fruiting bodies in the monokaryotic fis(c) strain and a dikaryon of Coprinus macrorhizus was inhibited by growth in high-glucose media. In high-glucose media the characteristic burst of adenosine 3',5'-cyclic monophosphate (cAMP) accumulation during fruiting-body formation was absent. Enzymatic activity assays revealed that mycelia grown in high-glucose media contained relatively lower amounts of adenylate cyclase and cAMP-phosphodiesterase than mycelia grown in low-glucose media. The synthesis of inducible d-serine deaminase and tryptophanase was repressed in high-glucose media. A mutant (gluR) in which the glucose repression of fruiting-body formation is affected was isolated by selection in high-glucose media. The mutation caused the cAMP levels to be no longer affected by glucose and affected ability to synthesize the inducible d-serine deaminase and tryptophanase. The gluR mutant was partially dominant in dikaryons. It is suggested that cAMP may play important roles in inducing fruiting bodies and in controlling inducible enzyme synthesis in C. macrorhizus.

Adenylyl Cyclases↗
PubMed1988

Genetic regulation of estrogen-dependent repression of female-specific testosterone 16 alpha-hydroxylase (I-P-450(16 alpha) in male mouse liver: murine Ripr locus.

The genetic basis for repression of I-P-450(16 alpha) in livers of male mice was examined in 129/J and BALB/cJ mice. Castration of adult male BALB/cJ but not 129/J mice resulted in derepression of I-P-450(16 alpha) at its mRNA and activity levels. It was further found that the patterns of derepression in (129/J x BALB/cJ) F1 and F2 offspring indicated that the derepression of I-P-450(16 alpha) is inherited as an autosomal additive trait. The distribution of derepression among castrated recombinant inbred strains (9 X A) indicated a close link of a locus repressing I-P-450(16 alpha) in male mice to the Rip locus on chromosome 7. Rip was previously defined as a locus that regulates specific expression of I-P-450(16 alpha) in livers of female mice [Noshiro, M., Lakso, M., Kawajiri, K., & Negishi, M. (1988) Biochemistry (preceding paper in this issue)]. Other tested inbred mice (A/HeJ, C57BL/6J, C3H/HeJ, and DBA/2J) showed the derepression of I-P-450(16 alpha) by castration, such as BALB/cJ. We propose Ripr (repression of an action of Rip locus in male mice) as the name of the locus by which repression of I-P-450(16 alpha) is regulated in male mice. Treatment of castrated male BALB/cJ mice by testosterone propionate, estradiol valerate, or diethylstilbestrol repressed I-P-450(16 alpha) to the levels seen in normal BALB/cJ male mice. Dihydrotestosterone, however, had little effect in repressing I-P-450(16 alpha) in castrated mice. The results suggested that estrogen rather than androgen is a repressor of I-P-450(16 alpha) in livers of male mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1977

Histidine production by a regulatory mutant of Streptomyces coelicolor.

Streptomyces coelicolor mutant RF-59, isolated as a revertant of a histidine auxotroph after mutagenic treatment with N-methylN'-nitro-N-nitrosoguanidine, was found to accumulate L-histidine. The mutant was sensitive to 2-thiazo-lealanine and L-2,4-diaminobutyric acid and partially sensitive to alpha-methylhistidine but resistant to 1,2,4-triazolealanine, indicating that repression of the histidine operon was modified in the mutant. Culture conditions were investigated, and optimal media for L-histidine production were developed, resulting in L-histidine accumulation of 2.1 to 3.5 g/liter.

Alanine↗
PubMed1978

Synthesis and activities of branched-chain aminoacyl-tRNA synthetases in threonine deaminase mutants of Escherichia coli.

Valyl-, isoleucyl-, and leucyl-tRNA synthetase activities were examined in an Escherichia coli K-12 strain that possessed a deletion of three genes of the ilv gene cluster, ilvD, A, and C, and in a strain with the same deletion that also carried the lambdadilvCB bacteriophage. It was observed that the branched-chain tRNA synthetase activities of both strains were considerably less than those of the normal strain during growth in unrestricted medium. Furthermore, during an isoleucine limitation, there was a further reduction in isoleucyl-tRNA synthetase activity and an absence of the isoleucine-mediated derepression of valyl-tRNA synthetase formation in both of these mutants, as compared with the normal strain. In addition, it was observed that these branched-chain synthetase activities were reduced in steady-state cultures of several ilvA point mutants. However, upon the introduction of the ilv operon to these ilvA mutants by use of lambda bacteriophage, there was a specific increase in the branched-chain synthetase activities to levels comparable to those of the normal strain. These results support our previous findings that the stability and repression control of synthesis of these synthetases require some product(s) missing in the ilvDAC deletion strain and strongly suggest this component is some form of the ilvA gene product, threonine deaminase.

Amino Acyl-tRNA Synthetases↗
PubMed1982

Cyclic AMP may not be involved in catabolite repression in Saccharomyes cerevisiae: evidence from mutants capable of utilizing it as an adenine source.

Mutants able to utilize 5'-AMP or cyclic AMP as the adenine source were isolated from an ade6 ade10 double mutant by ethyl methane sulfonate mutagenesis. A single amp1 mutation, primarily selected on 5'-AMP medium, confers the phenotype for utilization of exogenous 5'-AMP as the adenine source. From the ade6 ade10 amp1 triple mutant, a mutant able to utilize cyclic AMP was isolated, and the mutant phenotype was proven to be due to the simultaneous occurrence of triple mutations designated as cam1, cam2, and cam3. The cam3 mutation, but not cam1 or cam2, also confers the phenotype for utilizing 5'-AMP, the same phenotype as the amp1 mutation. All of these mutations are recessive to the respective wild-type counterparts. Cells having the ade6 ade10 amp1 cam1 cam2 cam3 genotype showed significant ability to take up exogenous cyclic AMP, whereas no differences were observed in cyclic AMP phosphodiesterase activity in comparison with that of the original strains used in the mutant isolation. Since glucose severely repressed galactokinase synthesis in the constitutive GAL81 mutant having the ade6 ade10 amp1 cam1 cam2 cam3 genotype, irrespective of the presence or absence of cyclic AMP in the medium, it was suggested that cyclic AMP is not involved in the mechanism of catabolite repression in Saccharomyces cerevisiae. It does, however, have a stimulative effect on the galactokinase synthesis in the GAL81 mutant in the absence of glucose.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Modulation of chromatin structure associated with derepression of the acid phosphatase gene of Saccharomyces cerevisiae.

We have analyzed the chromatin structure of a phosphate-repressible acid phosphatase gene (PHO5) within yeast nuclei. Under derepressed conditions (low Pi media), the gene is much more sensitive to either DNAse I or micrococcal nuclease digestion than is the repressed gene. We have mapped DNase I hypersensitive sites unique to the active gene near the 5'-end of the acid phosphatase mRNA and within a region presumed to function in the regulation of the gene by Pi. Although the gene is packaged into regularly spaced nucleosomes, no detectable phase relationship exists between nucleosomes and DNA sequence under derepressed conditions, whereas in the repressed state the nucleosomes occur in one predominant phase. These results demonstrate reversible changes in the chromatin structure of a eukaryotic gene system that directly correlate with the functional state of the gene.

Acid Phosphatase↗
PubMed2004

Growth and enzyme production by three Penicillium species on monosaccharides.

The growth and preference for utilisation of various sugar by the Penicillium species Penicillium pinophilum IBT 4186, Penicillium persicinum IBT 13226 and Penicillium brasilianum IBT 20888 was studied in batch cultivations using various monosaccharides as carbon source, either alone or in mixtures. P. pinophilum IBT 4186 and P. persicinum IBT 13226 had a micro(max) around 0.08-0.09 h(-1) using either glucose or xylose as carbon source. The micro(max) of P. brasilianum IBT 20888 was 0.16 and 0.14 h(-1) on glucose and xylose, respectively. Glucose was found to exert repression on the catabolism of mannose, galactose, xylose and arabinose. The three species were able to utilise all the tested monosaccharides, but arabinose was only slowly metabolised. Glucose was also found to repress the production of endoglucanases, endoxylanases and beta-xylosidases. After glucose depletion, the fungi started producing beta-glucosidase and endoglucanases. Xylose did not repress the enzyme production and it induced the production of endoxylanases and beta-xylosidases.

Fungal Proteins↗
PubMed1975

Regulation of Glutamine Transport in Escherichia coli.

The formation of the high-affinity (Km equal to 0.2 muM) L-glutamine transport system of Escherichia coli strain 7 (Lin) appears to be subject to the same major control as the glutamine synthetase (EC 6.3.1.2) of this gram-negative organism. Culture of cells under nitrogen-limited conditions provides maximum derepression of both the glutamine synthetase and the glutamine transport system. Nutritional conditions providing a rich supply of ammonium salts or available sources of nitrogen, i.e., conditions which repress the formation of glutamine synthetase, provide three- and 20-fold repression, respectively, of the glutamine transport system. Culture of cells with glutamine supplements of 2 mM does not increase the repression of high-affinity glutamine transport system beyond the level observed in the absence of glutamine. A second kinetically distinct low-affinity component of glutamine. A second kinetically distinct low-affinity component of glutamine uptake is observed in cells cultured with a glutamine-depleted nutrient broth. This second component is associated with the appearance of glutaminase A (EC 3.5.1.2) and asparaginase I (EC 3.5.1.1), a periplasmic enzyme. Parallel changes were observed in the levels of the high-affinity glutamine transport system and the glutamine synthetase when cells were cultured with the carbon sources: glucose, glycerol, or succinate.

Ammonia↗