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At least 235 records · Page 13Linked to original sources
PubMed1992

Identification and characterization of three genes that affect expression of ADH2 in Saccharomyces cerevisiae.

Using a new selection protocol we have identified and preliminarily characterized three new loci (ADR7, ADR8 and ADR9) which affect ADH2 (alcohol dehydrogenase isozyme II) expression. Mutants were selected which activate ADH2 expression in the presence of an over-expressed, normally inactive ADR1 allele. The mutants had very similar phenotypes with the exception that one was temperature sensitive for growth. In the absence of any ADR1 allele, the mutants allowed ADH2 to partially escape glucose repression. However, unlike wildtype strains deleted for ADR1, the mutants were able to efficiently derepress ADH2. The mutations allowed a small escape from glucose repression for secreted invertase, but had no effect on the glucose repression of isocitrate lyase or malate dehydrogenase. The mutations were shown to be nonallelic to a wide variety of previously characterized mutations, including mutations that affect other glucose-repressed enzymes.

Alcohol Dehydrogenase↗
PubMed1998

Control of the association state of tetrameric glucose-fructose oxidoreductase from Zymomonas mobilis as the rationale for stabilization of the enzyme in biochemical reactors.

Tetrameric, NADP-containing glucose-fructose oxidoreductase (GFOR) from Zymomonas mobilis catalyzes the oxidation of glucose into glucono-delta-lactone coupled to the reduction of fructose to sorbitol. GFOR is inactivated during substrate turnover in vitro, the long-term stability of the enzyme during conversions in biochemical reactors thereby being drastically reduced. The process of inactivation is triggered by structural transitions that are induced by the lactone product and involves aggregation as the ultimate cause of irreversible inactivation. Guanidinium hydrochloride-induced changes in the conformation of GFOR seem to be similar to those observed in the presence of lactone, and are manifested by incubation time-dependent increases in protein fluorescence and the solvent-exposed hydrophobic surface. The formation of high-order protein associates in solution in the presence of this denaturant proceeds from the native tetramer to a reversibly inactivated octamer and then to a dodecameric form that cannot be reactivated through spontaneous or assisted refolding. Therefore, stabilization of GFOR during turnover requires that the marked tendency of the enzyme to form aggregates is prevented efficiently. This goal has been accomplished in the presence of low urea concentrations (1.0 M), which led to a 10-fold increase in the half-life of GFOR under operational conditions.

Enzyme Repression↗
PubMed1995

The cyanobacterium Synechococcus sp. strain PCC 7942 contains a second alkaline phosphatase encoded by phoV.

A gene (phoV) encoding an alkaline phosphatase from Synechococcus sp. strain PCC 7942 was isolated by screening a plasmid gene bank for expression of alkaline phosphatase activity in Escherichia coli JM103. Two independent clones carrying the same alkaline-phosphatase-encoding gene were isolated. One of these clones (pKW1) was further analysed and the nucleotide sequence of a contiguous 3234 bp DNA fragment was determined. Two complete open reading frames (ORF1 and phoV) and an incomplete ORF3 were identified reading in the same direction. The deduced phoV gene product showed 34% identity to the alkaline phosphatase PhoA from Zymomonas mobilis, and the N-terminal part of the putative ORF3 protein exhibited 57% identity to a protein of unknown function from Frankia sp. Insertional inactivation of the Synechococcus PCC 7942 phoV gene failed, indicating an essential role for either the phoV or the ORF3 gene product. PhoV consists of 550 amino acid residues, resulting in a molecular mass of 61.3 kDa. To overexpress the Synechococcus PCC 7942 phoV gene in E. coli, plasmid pKW1 was transformed into a phoA mutant of E. coli (CC118). In E. coli strain CC118(pKW1) PhoV was expressed constitutively with high rates of activity, and was shown to be membrane associated in the periplasmic space. After partial purification of the recombinant PhoV, it was shown that, like other alkaline phosphatases, the Synechococcus PhoV had a broad pH optimum in the alkaline region and a broad substrate specificity for phosphomonoesters, required Zn2+ for activity, and was inhibited by phosphate. In contrast to several other alkaline phosphatases, PhoV was inhibited by Mn2+. Due to the lack of a Synechococcus PCC 7942 phoV mutant strain, the function of PhoV remains uncertain. However, the present results show that Synechococcus PCC 7942 has a second, probably phosphate-irrepressible, alkaline phosphatase (PhoV, 61.3 kDa) in addition to the phosphate-repressible enzyme (PhoA, 145 kDa) already described.

Alkaline Phosphatase↗
PubMed1995

IMP2, a gene involved in the expression of glucose-repressible genes in Saccharomyces cerevisiae.

Two mutants carrying different deletions of the IMP2 coding sequence of Saccharomyces cerevisiae, delta T1, which encodes a protein lacking the last 26 C-terminal amino acids, and delta T2, which completely lacks the coding region, were analysed for derepression of glucose-repressible maltose, galactose, raffinose and ethanol utilization pathways in response to glucose limitation. The role of the IMP2 gene product in the regulation of carbon catabolite repressible enzymes maltase, invertase, alcohol dehydrogenase, NAD-dependent glutamate dehydrogenase (NAD-GDH) and L-lactate:ferricytochrome-c oxidoreductase (L-LCR) was also analysed. The IMP2 gene product is required for the rapid glucose derepression of all above-mentioned carbon source utilization pathways and of all the enzymes except for L-LCR. NAD-GDH is regulated by IMP2 in the opposite way and, in fact, this enzyme was released at higher levels in both imp2 mutants than in the wild-type strain. Therefore, the product of IMP2 appears to be involved in positive and negative regulation. Both deletions result in growth and catalytic defects; in some cases partial modification of the gene product yielded more dramatic effects than its complete absence. Moreover, evidence is provided that the IMP2 gene product regulates galactose- and maltose-inducible genes at the transcriptional level and is a positive regulator of maltase, maltose permease and galactose permease gene expression.

Alleles↗
PubMed1990

Glutamine Synthetase is Expressed by Primary Sensory Neurons from Chick Embryos In Vitro but not In Vivo: Influence of Skeletal Muscle Extract.

Glutamine synthetase (GS) catalyses the ATP-dependent formation of glutamine from glutamate and ammonia. To determine whether dorsal root ganglion (DRG) cells from chick embryos express the enzyme in vivo or in vitro, GS was detected by immunocytochemical reaction either in vibratome sections of DRG or in dissociated DRG cell cultures. The immunocytochemical detection of GS showed that in vivo the DRG taken from chick embryos at day 10 (E10), E14, E18 or from chickens after hatching were free of any GS-positive ganglion cells; in contrast, in neuron-enriched cultures of DRG cells grown in vitro at E10, virtually all the neuronal cells (98.6 +/- 1.0%) express GS at 3, 5 or 7 days of culture. In mixed DRG cell cultures, only 83.6+/-4.6% of the neurons displayed a GS-immunoreactivity. In both culture conditions, neither the presence of horse serum nor the age of the culture appeared to affect the percentage of neurons which displayed a GS-immunoreactivity. After [3H]glutamine uptake, radioautographs revealed that only 80% of the neurons were labelled in neuron-enriched DRG cell cultures while 96% of the neurons were radioactive in mixed DRG cell cultures. Furthermore the most heavily [3H]glutamine-labelled neurons were exclusively found in mixed DRG cell cultures. Combination of both immunocytochemical detection of GS and radioautography after [3H]glutamine uptake showed that strongly GS-immunostained neurons corresponded to poorly radioactive ones and vice versa. When skeletal muscle extract (ME) was added to DRG cell cultures, the number of GS-positive neurons was reduced to 77.5 +/- 2.5% in neuron-enriched cultures or to 43.6 +/- 3.8% in mixed DRG cell cultures; in both types of culture, the intensity of the neuronal immunostaining was depressed. Furthermore, combined action of ME and non-neuronal cells potentiates the enzyme repression exerted separately by ME or non-neuronal cells. Since GS-immunoreactivity is expressed in DRG cells grown in vitro, but not in vivo, it is suggested that microenvironmental factors influence the expression of GS. More specifically, the repression of GS by primary sensory neurons grown in vitro may be strongly induced by soluble factors present in skeletal muscle, and to a lesser extent in brain, and potentiated by non-neuronal cells.

Journal Article↗
PubMed2001

Purification and characterization of aminopropionaldehyde dehydrogenase from Arthrobacter sp. TMP-1.

Aminopropionaldehyde dehydrogenase was purified to apparent homogeneity from 1,3-diaminopropane-grown cells of Arthrobacter sp. TMP-1. The native molecular mass and the subunit molecular mass of the enzyme were approximately 20,5000 and 52,000, respectively, suggesting that the enzyme is a tetramer of identical subunits. The apparent Michaelis constant (K(m)) for 1,3-diaminopropane was approximately 3 microM. The enzyme equally used both NAD(+) and NADP(+) as coenzymes. The apparent K(m) values for NAD(+) and NADP(+) were 255 microM and 108 microM, respectively. The maximum reaction rates (V(max)) for NAD(+) and NADP(+) were 102 and 83.3 micromol min(-1) mg(-1), respectively. Some tested aliphatic aldehydes and aromatic aldehydes were inert as substrates. The optimum pH was 8.0-8.5. The enzyme was sensitive to sulfhydryl group-modifying reagents.

Aldehyde Oxidoreductases↗
PubMed1975

Stimulation of derepressed enzyme synthesis in bacteria by growth on sublethal concentrations of chloramphenicol.

Culturing of Salmonella typhimurium or Escherichia coli cells in the presence of low concentrations (</=1 mug/ml) of chloramphenicol (CAP) permitted exponential growth, but at doubling times up to twice those of controls. When such cultures were subsequently starved for uracil or arginine, derepression of aspartate transcarbamylase (ATCase) or ornithine transcarbamylase, respectively, was enhanced three- to 10-fold as compared to cultures not exposed to CAP. Enhancement of beta-galactosidase synthesis by prior exposure to CAP was also observed in uracil-starved E. coli cultures. Stimulation of enzyme synthesis appeared to be a specific effect of CAP; low levels of erythromycin, puromycin, sparsomycin, tetracycline, and rifampin did not show such effects. Derepression of ATCase synthesis in exponentially growing cells in the presence of CAP did not result in stimulation of enzyme synthesis by CAP. A prior history of growth of a culture in the presence of CAP was shown to be necessary for enhancement of enzyme synthesis by CAP; furthermore, continued presence of CAP in the medium during starvation was not necessary for enhanced enzyme synthesis and inhibited it in some instances. Enhanced enzyme synthesis in starving, CAP-treated cultures could be blocked by rifampin, which suggested that CAP treatment allows prolonged or more extensive messenger ribonucleic acid synthesis.

Bacteria↗
PubMed2000

Antisense silencing of the creA gene in Aspergillus nidulans.

Antisense expression of a portion of the gene encoding the major carbon catabolite repressor CREA in Aspergillus nidulans resulted in a substantial increase in the levels of glucose-repressible enzymes, both endogenous and heterologous, in the presence of glucose. The derepression effect was approximately one-half of that achieved in a null creA mutant. Unlike results for that mutant, however, growth parameters and colony morphology in the antisense transformants were not affected.

Aspergillus nidulans↗
PubMed1970

Regulation of nitrate reductase in the basidiomycete Ustilago maydis.

Nitrate reductase was induced in Ustilago maydis by growth in medium containing only nitrate as the nitrogen source. Ammonium ions repressed the enzyme and led to a rapid loss of activity. Ammonium did not inhibit the enzyme in vitro; although amino acids partially did so, this cannot account for the rapid loss of in vivo activity which occurred when the ammonium was added. Experiments with cycloheximide and actinomycin D, together with measurements of protein turnover, suggested that nitrate reductase is actively broken down when cells with fully induced activity are transferred to medium containing ammonium ions.

Basidiomycota↗
PubMed1977

Selective inhibition of Bacillus subtilis sporulation by acridine orange and promethazine.

Two structurally similar compounds were found to inhibit sporulation in Bacillus subtilis 168. A dye, acridine orange, and an antischizophrenic drug, promethazine, blocked spore formation at concentrations subinhibitory to vegetative growth, while allowing synthesis of serine protease, antibiotic, and certain catabolite-repressed enzymes. The sporulation process was sensitive to promethazine through T2, whereas acridine orange was inhibitory until T4. The drug-treated cells were able to support the replication of phages phie and phi29, although the lytic cycles were altered slightly. The selective inhibition of sporulation by these compounds may be related to the affinity of some sporulation-specific genes to intercalating compounds.

Acridines↗