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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The GLN3 gene of Saccharomyces cerevisiae is required for the activation of transcription of a number of genes in response to the replacement of glutamine by glutamate as source of nitrogen. We cloned the GLN3 gene and constructed null alleles by gene disruption. GLN3 is not essential for growth, but increased copies of GLN3 lead to a drastic decrease in growth rate. The complete nucleotide sequence of the GLN3 gene was determined, revealing one open reading frame encoding a polypeptide of 730 amino acids, with a molecular weight of approximately 80,000. The GLN3 protein contains a single putative Cys2/Cys2 zinc finger which has homology to the Neurospora crassa NIT2 protein, the Aspergillus nidulans AREA protein, and the erythroid-specific transcription factor GATA-1. Immunoprecipitation experiments indicated that the GLN3 protein binds the nitrogen upstream activation sequence of GLN1, the gene encoding glutamine synthetase. Neither control of transcription nor control of initiation of translation of GLN3 is important for regulation in response to glutamine availability.
Mol Cell Biol 1991 Dec
PMID:Sequence and expression of GLN3, a positive nitrogen regulatory gene of Saccharomyces cerevisiae encoding a protein with a putative zinc finger DNA-binding domain. 168

We analyzed the upstream region of the GDH2 gene, which encodes the NAD-linked glutamate dehydrogenase in Saccharomyces cerevisiae, for elements important for the regulation of the gene by the nitrogen source. The levels of this enzyme are high in cells grown with glutamate as the sole source of nitrogen and low in cells grown with glutamine or ammonium. We found that this regulation occurs at the level of transcription and that a total of six sites are required to cause a CYC1-lacZ fusion to the GDH2 gene to be regulated in the same manner as the NAD-linked glutamate dehydrogenase. Two sites behaved as upstream activation sites (UASs). The remaining four sites were found to block the effects of the two UASs in such a way that the GDH2-CYC1-lacZ fusion was not expressed unless the cells containing it were grown under conditions favorable for the activity of both UASs. This complex regulatory system appears to account for the fact that GDH2 expression is exquisitely sensitive to glutamine, whereas the expression of GLN1, coding for glutamine synthetase, is not nearly as sensitive.
Mol Cell Biol 1991 Dec
PMID:Role of the complex upstream region of the GDH2 gene in nitrogen regulation of the NAD-linked glutamate dehydrogenase in Saccharomyces cerevisiae. 168 1

The complete nucleotide sequence of the open reading frame (ORF) located upstream of the glnA structural gene for glutamine synthetase (GS) in Azospirillum brasilense Sp7 was determined. This ORF, which codes for a 12 kDa protein, was identified as glnB, the structural gene for the PII protein, a component of the adenylylation cascade involved in the regulation of GS activity in some gram-negative bacteria. Transcription analysis and mRNA mapping of glnB and glnA of A. brasilense was performed with bacteria grown under different physiological conditions. The glnA gene can be transcribed either as a glnB-A mRNA of 2.4 kb or as a glnA mRNA of 1.5 kb. Differential expression of the two mRNAs was found to depend on the nitrogen source. The glnB-A mRNA was the major transcript under nitrogen fixation conditions, while the synthesis of the glnA mRNA was almost completely abolished. The glnA mRNA was predominantly produced in NH4(+)-containing medium. Transcription start site analysis revealed the presence of three different types of nitrogen-regulated promoters. GlnB-A mRNA was transcribed selectively from tandem promoters. One of them is similar to the NtrA-dependent promoter and the other to the Escherichia coli sigma 70 promoter. The synthesis of glnA mRNA was regulated by a promoter, which was repressed (or non-activated) only under conditions of nitrogen fixation, when moleuclar nitrogen was the sole nitrogen source. The transcriptional initiation site in front of glnA is not preceded by a canonical E. coli sigma 70 promoter. A sequence reminiscent of the NtrA-dependent promoter consensus, except for a fundamental mismatch, was found at positions -33 to -21. This sequence overlapped a putative "weak" NtrC-binding site, similar to those identified in enteric bacteria. From these results, it is postulated that glnA mRNA is controlled by a novel type of nitrogen-regulated promoter.
Mol Gen Genet 1990 Dec
PMID:Characterization of three different nitrogen-regulated promoter regions for the expression of glnB and glnA in Azospirillum brasilense. 170 7

We describe the cloning of the glutamine synthetase 1 (GS1) gene based on cross-homology with the glutamine synthetase 2 (GS2) gene in Drosophila melanogaster. We have determined the GS gene number in the Drosophila genome, and we describe the isolation of cDNA clones corresponding to the two isoforms, their entire sequence and their transcription pattern. We looked for subcellular localization of one enzymic isoform; in this way, we were able to locate the GS1 enzyme within the mitochondria of D. melanogaster. We have compared different GS sequences from plants and humans; emerging evolutionary implications are discussed. In addition, we have identified a certain highly stable secondary structure at the nucleotide level in the coding region of isoforms located in the organella.
J Mol Biol 1990 Mar 05
PMID:Homologous nuclear genes encode cytoplasmic and mitochondrial glutamine synthetase in Drosophila melanogaster. 196 91

The expression of glutamine synthetase (GS) in the rat liver is dependent on pituitary growth hormone (GH). RNA blot hybridizations revealed that in hypophysectomized rats the level of glutamine synthetase mRNA was dramatically reduced in liver but not brain. This drop of GS mRNA in the liver results in a reduction of GS enzyme activity as well. Two other messages, phosphoenolpyruvate carboxykinase and glycerol phosphate dehydrogenase were not diminished in the liver, indicating that the effects of hypophysectomy on hepatic GS expression are specific and not part of a general reduction in transcription due to lack of pituitary factors. Daily administration of rat pituitary growth hormone caused an increase in the levels of hepatic GS mRNA as well as enzyme activity. In situ hybridization of normal liver sections with the GS antisense message showed an abundant amount of message confined to the region around each central vein of the hepatic acini, while in the hypophysectomized animal the message for GS is greatly reduced but still only located in hepatocytes surrounding the central vein. Hypophysectomized animals given GH replacement showed a substantial increase in the amount of exposed silver grains only around the central veins. This indicates that GH does not influence the cellular position of GS expression nor the viability of those hepatocytes that express the enzyme, but it does regulate the quantity of GS in the liver through changes in the levels of GS mRNA.
Mol Cell Endocrinol 1990 Mar 05
PMID:Growth hormone regulation of hepatic glutamine synthetase mRNA levels in rats. 197 Mar 14

The glnA gene of the thermophilic sulphur-dependent archaebacterium Sulfolobus solfataricus was identified by hybridization with the corresponding gene of the cyanobacterium Spirulina platensis and cloned in Escherichia coli. The nucleotide sequence of the 1696 bp DNA fragment containing the structural gene for glutamine synthetase was determined, and the derived amino acid sequence (471 residues) was compared to the sequences of glutamine synthetases from eubacteria and eukaryotes. The homology between the archaebacterial and the eubacterial enzymes is higher (42%-49%) than that found with the eukaryotic counterpart (less than 20%). This was true also when the five most conserved regions, which it is possible to identify in both eubacterial and eukaryotic glutamine synthetases, were analysed.
Mol Gen Genet 1990 Apr
PMID:Cloning and nucleotide sequence of an archaebacterial glutamine synthetase gene: phylogenetic implications. 197 23

Analysis of induction of glutamine synthetase activity by dexamethasone showed a 2-fold increase in NIH3T3 but no change in NIH3T3 ras (EJ-ras) cells. The observed increase could be abolished by the antagonist RU486. The lack of response in ras transformed cells might reflect oncoprotein effects on the glucocorticoid receptor (GR). Several GR parameters were studied in order to clarify this point. Total GR level was the same for both cells; cytoplasmic receptor level however, was 3 times lower in NIH3T3 ras than in NIH3T3 cells. Hormone-receptor binding affinity, specificity, thermostability, sedimentation coefficient, molecular weight as well as the cytoplasmic GR transformation ratio were similar for the two cell lines. On the other hand, the fraction of the total receptor pool involved with the recycling process was approximately 20% lower in NIH3T3 ras than in NIH3T3 cells. After 24 h of dexamethasone treatment, no GR down regulation was observed in NIH3T3 ras cells, whereas normal NIH3T3 cells exhibited a decrease of GR binding capacity around 80%. Further studies are necessary to define the mechanisms underlying the association between glucocorticoid insensitivity, and modifications in the GR nuclear/cytoplasmic ratio, in the recycling GR fraction and in the down-regulation process observed in ras transformed cells.
J Steroid Biochem Mol Biol 1990 Oct
PMID:The effects of ras gene expression on glucocorticoid receptors in mouse fibroblasts. 198 81

Using glnT DNA of Rhizobium meliloti as a hybridization probe we identified a R. leguminosarum biovar phaseoli (R. l. phaseoli) locus (glnT) expressing a glutamine synthetase activity in Klebsiella pneumoniae. A 2.2 kb DNA fragment from R. l. phaseoli was cloned to give plasmid pMW5a, which shows interspecific complementation of a K. pneumoniae glnA mutant. The cloned sequence did not show cross-hybridization to glnA or glnII, the genes coding for two glutamine synthetase isozymes of Rhizobium spp. While in previous reports on glnT of R. meliloti and Agrobacterium tumefaciens no glutamine synthetase activity was detected, we do find activity with the glnT locus of R. l. phaseoli. The glutamine synthetase (GSIII) activity expressed in a K. pneumoniae glnA strain from pMW5a shows a ratio of biosynthetic to transferase activity 10(3)-fold higher than that observed for GSI or GSII. GSIII is similar in molecular weight and heat stability to GSI.
Mol Gen Genet 1990 Sep
PMID:A previously unrecognized glutamine synthetase expressed in Klebsiella pneumoniae from the glnT locus of Rhizobium leguminosarum. 198 Jan 42

Glutamate in glutamatergic neurons exists in a cytosolic pool, as well as a transmitter pool, which is assumed to be localized in synaptic vesicles. Transmitter glutamate released from glutamatergic neurons is taken up by both neurons and glial cells, giving rise to a flux of glutamate from neurons to astrocytes. In astrocytes, glutamine is formed from glutamate by the glial-specific enzyme glutamine synthetase (EC 6.3.1.2). Glutamine diffuses back to neurons, where glutamate is formed by phosphate-activated glutaminase (EC 3.5.1.2). However, this cycle is not stoichiometric, and glutamine obtained from glial cells cannot replenish all transmitter glutamate lost from neurons. 2-Oxoglutarate is another putative precursor for transmitter glutamate. Net synthesis of citric acid cycle intermediates is dependent on carbon dioxide fixation to pyruvate, catalyzed by pyruvate carboxylase (EC 6.4.1.1). Since this enzyme is exclusively glial, a net flow of citric acid cycle intermediates from glial cells to neurons probably exists. The quantitative contribution of each transmitter precursor may not be the same in different regions of the brain and may vary with the metabolic state of the neuron. The pool of transmitter glutamate is most likely regulated by the activity of glutamate-forming enzymes in the nerve terminal, and/or by uptake/release of glutamate and glutamate precursors through the synaptosomal plasma membrane.
Mol Chem Neuropathol 1990 Jan
PMID:Synthesis of transmitter glutamate and the glial-neuron interrelationship. 198 May 84

The Clostridium acetobutylicum glnA gene has two transcript start sites under the control of promoters p1 and p2. Initiation of transcription was regulated by nitrogen and a downstream region was implicated in the regulation of transcript initiation by nitrogen in Escherichia coli. Putative antisense RNA was produced from a single downstream transcript start site under the control of p3. An up-promoter mutation in p3 resulted in lower levels of glutamine synthetase (GS) activity. Putative antisense RNA had a role in down-regulating GS expression but was not involved in regulation by nitrogen. Deletion of downstream inverted repeat sequences resulted in very low levels of GS activity.
Mol Microbiol 1990 Sep
PMID:Studies on Clostridium acetobutylicum glnA promoters and antisense RNA. 198 Oct 87


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