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PubMed1975

Isolation of super-repressor mutants in the histidine utilization system of Salmonella typhimurium.

Two super-repressor mutations in the histidine utilization (hut) operons of Salmonella typhimurium are described. Cells bearing either of these mutations have levels of hut enzymes that do not increase above the uninduced levels when growth is in the presence of either histidine or the gratuitous inducer imidazole propionate. Both mutations lie in the region of the gene for the hut repressor, hutC, and reverse mutations of both are to the constitutive (repressor-negative) rather than to the inducible (wild type) phenotype. In hybrid merodiploid strains the super-repressor mutations are dominant over either wild-type (hutC+) or repressor-negative (hutC-) alleles. Whereas both super-repressor mutations cause the uninducible synthesis of hut enzymes, the degree of repression is different. One mutation causes repression of enzyme synthesis in one of the two hut operons to a level below the basal, uninduced level of wild-type cells. The other mutation causes repression to a lesser degree than in wild-type cells, so that the hut enzymes are present at a level above the normal basal level; this partially constitutive synthesis is greater for the enzymes of one of the hut operons than for the enzymes of the other. Thus, both mutations apparently result in repressors with altered operator-binding properties, in addition to altered inducer-binding properties.

Alleles↗
PubMed1978

Regulation of the beta-1,3-glucanase system in Penicillium italicum: glucose repression of the various enzymes.

The microscopic fungus Penicillium italicum when grown in a synthetic liquid medium produced at least three enzymes with beta-1,3-glucanase activity which were separated by diethylaminoethyl-Sephadex column chromatography. These were named beta-1,3-glucanases I, II, and III respective to their order of elution from the column. A tentative characterization of these three enzymes indicated that they have different modes of action; the first one is an endoglucanase, the second is an exoglucanase, and the third probably has both mechanisms of action. Glucose had a repressive effect on all three enzymes. Only small amounts of beta-1,3-glucanases II and III were present in the cells when they were actively growing in the presence of this sugar. However, when the cells were transferred to a medium low in glucose, a significant increase in the specific activity of beta-1,3-glucanase took place; this was due in part to a much more active production of beta-1,3-glucanases II and III and in part to the appearance of beta-1,3-glucanase I, which could only be detected after more than 12 h of incubation in this medium. The results are discussed in the context of possible beta-1,3-glucanase functions in the fungal cells.

Chromatography, Ion Exchange↗
PubMed1969

Enzymes of tryptophan biosynthesis in Serratia marcescens.

In Serratia marcescens, the tryptophan biosynthetic enzymes were formed coordinately. A number of tryptophan auxotrophs showed single biochemical lesions; several mutants showed pleiotropic effects. Sucrose density gradient centrifugation revealed an unique pattern of migration of the tryptophan biosynthetic enzymes. The repression response of the Serratia enzymes to exogenous tryptophan was fivefold more sensitive than that found in Escherichia coli. When this information is contrasted with the available information on the other Enterobacteriaceae, one is compelled to conclude that S. marcescens enjoys a rather marked evolutionary divergence from the other enteric organisms.

Enzyme Repression↗
PubMed1978

Evidence for translational repression of arginine biosynthetic enzymes in Escherichia coli: altered regulation in a streptomycin-resistant mutant.

The formation and repressibility of the arginine biosyntietic enzymes acetylornithine delta-aminotransferase (EC 2.6.1.11), acetylornithine deacetylase (EC 3.5.1.16), ornithine carbamoyltransferase (EC 2.1.3.3), and argininosuccinate lyase (EC 4.3.2.1) were studied in an Escherichia coli W derivative (strain 250-10) that carries (a) a mutant allele of the argR regulatory gene causing a diminished repression-derepression range and (b) a streptomycin resistance mutation. In comparison with the streptomycin-sensitive parent 250, all four enzymes (a) are formed as smaller proportions of the total protein (overall range, 12% to 71%), whether the conditions are repressive (arginine excess) or derepressive (arginine restriction), and (b) show increased repressibility ratios, the carbamoyltransferase giving the largest increase (from 5.7 to 25.0). These effects appear to depend on the concurrent expression of the regulatory-gene and streptomycin resistance mutations, as indicated by analogous experiments with canavanine-resistant mutants of 250-10 that have partial argR- character. The results provide evidence for translational repression in the arginine system, and are interpreted in terms of a functional interaction of a mutant arginine repressor with a mutant S12 ribosomal protein. The locale of translational repression may be near the site of S12, and this mode of regulation may involve initiational selectivity of groupwise recognizable arginine messenger RNA's.

Acetamides↗
PubMed1979

Carbon and nitrogen repression of arginine catabolic enzymes in Bacillus subtilis.

Specific activities of arginase and ornithine aminotransferase, inducible enzymes of arginine catabolism in Bacillus subtilis 168, were examined in cells grown with various carbon and nitrogen sources. Levels of these enzymes were similar in arginine-induced cultures whether glucose or citrate was the carbon source (in contrast to histidase), suggesting that carbon source catabolite repression has only limited effect. In media with combinations of nitrogen sources, glutamine strongly repressed induction of these enzymes by proline or arginine. Ammonium, however, only repressed induction by proline and had no effect on induction by arginine. These effects correlate with generation times in media containing these substances as sole nitrogen sources: growth rates decreased in the order glutamine-arginine-ammonium-proline. Similar phenomena were observed when glutamine or ammonium were added to arginine- or proline-grown cultures, or when arginine or proline were added to glutamine- or ammonium-grown cultures. In the latter cases, an additional feature was apparent, namely a surprisingly long transition between steady-state enzyme levels. The results are compared with those for other bacteria and for eucaryotic microorganisms.

Arginase↗
PubMed1976

The regulation of diaminopimelate decarboxylase activity in Escherichia coli strain w.

Activity of diaminopimelate decarboxylase in Escherichia coli strain W, growing in an aerated fermenter, was only slightly (14%) repressed by 2 mM-lysine when approximately equimolar diaminopimelate was present in the medium. Lysine alone caused 78% repression. Diaminopimelate did not interfere with uptake of lysine by growing organisms. Organisms grown in medium containing diaminopimelate, without lysine, had a decarboxylase activity 24% higher than organisms from minimal medium. The extent of repression by pyridoxine (56% when added to minimal medium) was decreased (to 31%) when diaminopimelate was also present in the medium. A diaminopimelate-requiring mutant, with limited ability to take up diaminopimelate, formed almost three times less diaminopimelate decarboxylase than did a diaminopimelate-requiring second-stage mutant that had an increased rate of transport of this amino acid. The internal concentration of diaminopimelate thus probably regulates the activity of the decarboxylase by induction. Lysine might not directly repress the enzyme but might give an apparent repression by restricting the biosynthesis of diaminopimelate. This restriction is probably not caused only by inhibition or repression of aspartokinase. Lysine and threonine together, though not singly, almost completely inhibited aspartokinase in vitro but caused less apparent repression of diaminopimelate decarboxylase than did lysine alone. Lysine plus diaminopimelate strongly repressed the lysine-sensitive aspartokinase (85%) without much affecting diaminopimelate decarboxylase formation, and pyridoxine repressed the decarboxylase without affecting aspartokinase.

Aspartate Kinase↗
PubMed1995

Purification and characterization of the arylsulfatase synthesized by Pseudomonas aeruginosa PAO during growth in sulfate-free medium and cloning of the arylsulfatase gene (atsA).

An arylsulfatase (EC 3.1.6.1) was extracted from Pseudomonas aeruginosa PAO1 and purified 2700-fold to homogeneity. Synthesis of this enzyme was repressed when sulfate, cysteine or thiocyanate was supplied as the sole sulfur source for growth, but derepressed with all other sulfur sources tested. The apparent molecular mass was determined by SDS/PAGE to be 57 kDa, and the enzyme was presumed to be a monomer after gel filtration chromatography. The arylsulfatase showed maximal activity at 57 degrees C and pH 8.9, and a Km of 105 microM for 4-nitrocatecholsulfate. Despite previous reports that both inducible and derepressible forms of arylsulfatase exist in P. aeruginosa, we found only one enzyme under a variety of growth conditions: a sulfate-repressed enzyme with a native isoelectric point of 4.76. The gene encoding this enzyme (atsA) was isolated by complementation of a Tn5-751 mutant of P. aeruginosa PAO1. Sequencing revealed a 1602-bp reading frame encoding a 534-amino-acid protein with sequence similarity to known bacterial and eukaryotic arylsulfatases (30-40% and 25-30% identity, respectively), but lacking the signal peptide which is present in all known sequences. The lack of this signal peptide suggests that the P. aeruginosa arylsulfatase is neither periplasmic nor membrane-associated, unlike other known arylsulfatases. The atsA gene was located at 15-17' on the P. aeruginosa genome by Southern hybridization. Only a single copy was observed under moderate stringency conditions.

Amino Acid Sequence↗
PubMedDate not supplied

[Glucose catabolite repression of glucoamylase biosynthesis by the yeast Endomycopsis fibuligera].

The effect of glucose, sucrose, fructose, maltose, alpha-methyl glucoside, glycerol, nonmetabolizing glucose analog--2-deoxy-D-glucose, and cyclic 3',5'-adenosine monophosphate (cAMP) on the glucoamylase biosynthesis by the yeast Endomycopsis fibuligera 20-9 was investigated. The sugars tested induced repression of the enzyme synthesis. The repressive effect of glucose, sucrose and maltose was reversed partially or completely by cAMP. The strongest derepressive effect of cAMP was noted in the presence of 2-deoxy-D-glucose. The transport of glucose and 2-deoxy-D-glucose in yeast cells was also investigated. Those compounds were found to compete for the entry into the cell. It is concluded that glucoamylase synthesis in Endomycopsis fibuligera 20-9 was susceptible to catabolite repression. Its possible mechanism discussed.

Ascomycota↗
PubMed1999

Enzymic characterization of a novel member of the regulatory B-like carboxypeptidase with transcriptional repression function: stimulation of enzymic activity by its target DNA.

The adipocyte-enhancer binding protein (AEBP) 1 is a novel transcriptional repressor with carboxypeptidase (CP) activity. AEBP1 binds to a regulatory sequence (termed adipocyte enhancer 1, AE-1) located in the proximal promoter region of the adipose P2 (aP2) gene, which encodes the adipocyte fatty-acid binding protein. Sequence comparisons and kinetic studies using known carboxypeptidase substrates, activators and inhibitors have characterized AEBP1 as a member of the regulatory B-like CP family. Significantly, the inherent CP activity of AEBP1 is stimulated by the AE-1 sequence. Our results indicate that AEBP1 is activated by a novel mechanism, wherby the direct binding of DNA enhances its protease activity. These results represent the first demonstration of DNA-mediated regulation of CP activity.

Binding Sites↗
PubMed1976

Regulation of branched-chain amino acid biosynthesis.

Formation of branched-chain amino acids in microorganisms is controlled mainly by end-product inhibition of the enzyme action but also by repression of enzyme synthesis. The two mechanisms may be interrelated. Regulation of the metabolite flow by end-product inhibition is realized by the inhibition of threonine deaminase by isoleucine; inhibition of acetohydroxy acid synthetase by valine and inhibition of alpha-isopropylmalate synthetase by leucine. Acetohydroxy acid synthetase has a key position in the pathway, since the enzyme catalyzes not only the synthesis of acetolactate, the valine and isoleucine precursor from pyruvate, but also that of acetohydroxybutyrate, the isoleucine precursar from alpha-ketobutyrate and pyruvate. Quenching of valine pathway by valine would be expected to be accompanied by a quenching of the isoleucine pathway as well. Nevertheless, aceto-hydroxybutyrate is formed rather than acetolactate, since alpha-ketobutyrate has a greater affinity to the enzyme than pyruvate and the inhibitory effect of valine is directly proportional to substrate concentration. It could completely reverse the inhibition. Regulation on the physiological level of the pathways to the branched-chain amino acids occurs by the repression of the leucine and isoleucine-valine biosynthetic enzymes. A phenotypic derepression caused by valine was detectable in the case of the latter biosynthetic enzymes. The idea that aminoacyl tRNA formation is a necessary reaction in the formation of the 'repressor" has been supported by numerous data. Indeed, some of the latest reports suggest that aminoacyl tRNA interaction with feedback sensitive enzyme may play an important role in the repression.

2-Isopropylmalate Synthase↗
PubMed1983

Periodic enzyme synthesis and oscillatory repression: why is the period of oscillation close to the cell cycle time?

During exponential growth of a cell culture, some enzymes are synthesized periodically. In a synchronous culture, in which all cells undergo DNA synthesis and division more-or-less synchronously, the burst of enzyme synthesis also occurs synchronously in each cell once per division cycle. However, there are a number of interesting cases in which periodic enzyme synthesis continues in the absence of synchronous DNA replication or cell division. In all cases of periodic enzyme synthesis in asynchronous cultures, the time between bursts of enzyme synthesis, though no longer identical to the cell cycle time, is still close to the interdivision time of the growing, replicating cells. The theory of oscillatory repression looks for an explanation of this phenomenon in the periodic repression of gene transcription caused by periodic fluctuations in the concentration of the endproduct of the metabolic pathway of which the enzyme is a part. A major difficulty with this theory is that there is no obvious relationship between the periodicity of the negative feedback loop, which is determined by the kinetics of synthesis and degradation of the individual components of the feedback loop, and the periodicity of the cell cycle, which is determined by overall net synthetic rates of cellular macromolecules. Why should the period of oscillation of a repressible gene transcription system be close to the interdivision time of a population of growing cells? In this paper, I show that the relationship may be coincidental: the two fundamental periods are close to each other because they are both close to the mass-doubling time of the cell culture. That the mean interdivision time must be close to the mass-doubling time is a consequence of "balanced" growth: there is a stable size distribution of cells in a growing culture. That the period of oscillation of the negative feedback loop is also close to the mass-doubling time is shown to be a consequence of the large, nearly constant demand for endproduct and the assumed stability of the enzyme. The period of oscillation is largely attributable to the slow dilution of the stable enzyme by cell growth. For reasonable values of the parameters describing the gene-control system, I show that the enzyme must be diluted by a factor of two (approximately), that is, by the growth accomplished by one mass-doubling (nearly).

Cell Cycle↗
PubMed1975

Induction of enzymes by glucagon, glucose repression, adenosine 3',5'-monophosphate concentration during carcinogenesis and in Morris 6918A hepatoma.

We have studied glucagon induction of enzymes, adenosine 3', 5'-monophosphate concentrations, and glucose repression in Morris 9618A hepatoma and in the liver of rats fed, for periods of up to 5 weeks, a solid diet containing 2-acetylaminofluorene or 3'-methyl-4-dimethylaminoazobenzene. While the basal levels of the enzymes serine dehydratase and tyrosine aminotransferase were the same as those found in control rats, their response to glucagon was reduced in experimental animals with or without tumors. However, the basal or glucagon-stimulated levels of adenosine 3', 5'-monophosphate in the liver of rats given the carcinogens were not changed. In Morris 9618A hepatoma, these parameters were, likewise, comparable to those in control animals. When glucose was administered to carcinogen-treated or tumor-bearing rats that had received a single dose of glucagon, there was no suppression of the increase in activity of serine dehydratase and tyrosine aminotransferase observed after glucagon treatment alone. The loss of glucose repression was seen already at 2 to 3 weeks following initiation of the carcinogenic diets. As previous studies had established for normal liver, the hormone-induced high levels of adenosine 3',5'-monophosphate remained unchanged also in Morris 9618A hepatoma and in rats given carcinogen. These results indicate that alterations in enzyme induction during chemical carcinogenesis are not the consequence of changes in adenosine 3',5'-monophosphate levels caused by carcinogens. The early disappearance of the glucose effect, which persists in slow-growing hepatomas, may be an expression of interference by carcinogens with the translation apparatus of the hepatic cell.

Animals↗
PubMed1987

GAL4 of Saccharomyces cerevisiae activates the lactose-galactose regulon of Kluyveromyces lactis and creates a new phenotype: glucose repression of the regulon.

A Kluyveromyces lactis mutant defective in lac9 cannot induce beta-galactosidase or galactokinase activity and is unable to grow on lactose or galactose. When this strain was transformed with the GAL4 positive regulatory gene of Saccharomyces cerevisiae it was able to grow on lactose or galactose as the sole carbon source. Transformants bearing GAL4 exhibited a 4.5-h generation time on galactose or lactose, versus 24 h for the nontransformed lac9 strain. A K. lactis lac9 strain bearing two integrated copies of GAL4 showed 3.5-fold induction of beta-galactosidase activity and 1.8-fold induction of galactokinase activity compared with 15.6-fold and 4.4-fold induction, respectively, for the LAC9 wild-type strain. In transformants bearing 10 integrated copies of GAL4, the induced level of beta-galactosidase was nearly as high as in the LAC9 wild-type strain. In addition to restoring lactose and galactose gene expression, GAL4 in K. lactis lac9 mutant cells conferred a new phenotype, severe glucose repression of lactose and galactose-inducible enzymes. Glucose repressed beta-galactosidase activity 35- to 74-fold and galactokinase activity 14- to 31-fold in GAL4 transformants, compared with the 2-fold glucose repression exhibited in the LAC9 wild-type strain. The S. cerevisiae MEL1 gene was repressed fourfold by glucose in LAC9 cells. In contrast, the MEL1 gene in a GAL4 lac9 strain was repressed 20-fold by glucose. These results indicate that the GAL4 and LAC9 proteins activate transcription in a similar manner. However, either the LAC9 or GAL4 gene or a product of these genes responds differently to glucose in K. lactis.

Enzyme Induction↗