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Query: UNIPROT:P06889 (Mol)
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A barley leaf cDNA library has been screened with two oligonucleotide probes designed to hybridize to conserved sequences in glutamine synthetase (GS) genes from higher plants. Two GS cDNA clones were identified as hybridizing strongly to one or both probes. The larger clone (pcHvGS6) contained a 1.6 kb insert which was shown by primer extension analysis to be an almost full-length cDNA. Both clones were more closely related to cDNAs for the chloroplast form of GS (GS2) from pea and Phaseolus vulgaris than to cDNAs for the cytosolic form (GS1). A sequence identical to an N-terminal sequence determined from a purified preparation of the mature GS2 polypeptide (NH2-XLGPETTGVIQRMQQ) was found in the pcHvGS6-encoded polypeptide at residues 46-61, indicating a pre-sequence of at least 45 amino acids. The pre-sequence has only limited sequence homology to the pre-sequences of pea and P. vulgaris GS2 subunits, but is similarly rich in basic residues and possesses some of the structural features common to the targeting sequences of other chloroplast proteins. The molecular lesions responsible for the GS2-deficient phenotypes of eight photorespiratory mutants of barley were investigated using a gene-specific probe from pcHvGS6 to assay for GS2 mRNA, and an anti-GS antiserum to assay for GS2 protein. Three classes of mutants were identified: class I, in which absence of cross-reacting material was correlated with low or undetectable levels of GS2 mRNA; class II, which had normal or increased levels of GS2 mRNA but very little GS2 protein; and class III, which had significant amounts of GS2 protein but little or no GS2 activity.
Plant Mol Biol 1990 Mar
PMID:Molecular analysis of barley mutants deficient in chloroplast glutamine synthetase. 198 86

In this paper we have examined whether the four glutamine synthetase (gln) genes, expressed in roots and nodules of Phaseolus vulgaris are substrate-inducible by ammonium. Manipulation of the ammonium pool in roots, through addition and removal of exogenous ammonium, did not elicit any changes in the abundances of the four mRNAs thus suggesting that the gln genes in roots of this legume are neither substrate-inducible by ammonium nor derepressed during nitrogen starvation. In nodules the effect of the ammonium supply on expression of the gln genes has been examined by growing nodules under argon/oxygen atmospheres, or with a number of Fix- Rhizobium mutants, and following addition of exogenous ammonium. The results of these experiments suggest that the expression of the gln-gamma gene, which is strongly induced during nodule development, is primarily under a developmental control. However nitrogen fixation appears to have a quantitative effect on expression of gln-gamma as the abundance of this mRNA is about 2 to 4-fold higher under nitrogen-fixing conditions. This effect could not be mimicked by addition of exogenous ammonium and moreover is not specific to the gln-gamma gene as mRNA from a leghaemoglobin gene was similarly affected. Taken together these results have failed to find an effect of ammonium on specifically inducing the expression of glutamine synthetase genes in roots and nodules of P. vulgaris.
Plant Mol Biol 1990 Apr
PMID:Expression of glutamine synthetase genes in roots and nodules of Phaseolus vulgaris following changes in the ammonium supply and infection with various Rhizobium mutants. 198 88

A full-length cDNA encoding glutamine synthetase was isolated from a lambda gt11 library constructed from the poly(A)+ RNA isolated from lettuce seeds incubated under red light. The nucleotide sequence of the cDNA and the deduced sequence of amino acids showed a high degree of homology to those of the cytosol-type glutamine synthetase from other plants. Northern and dot-blot analyses of poly(A)+ RNA extracted from the seeds incubated under various light conditions showed that the activation of the gene for cytosolic glutamine-synthetase during imbibition of lettuce seeds is directly or indirectly regulated by phytochrome.
Plant Mol Biol 1990 Aug
PMID:Phytochrome-mediated activation of the gene for cytosolic glutamine-synthetase (GS1) during imbibition of photosensitive lettuce seeds. 198

Two transgenic tobacco lines were genetically engineered to contain chimaeric genes encoding the glutamine synthetase (GS) gamma polypeptide of Phaseolus vulgaris (French bean), expressed from the cauliflower mosaic virus 35S promoter. One (MIT-1) contained two copies of a construct including the first 60 amino acids of the Nicotiana plumbaginifolia beta-F1 ATPase to target the GS polypeptide to the mitochondrion. The other (CYT-4) contained a single copy of a cytosolic GS construct. Leaves of in vitro plantlets expressed the constructs and contained a novel GS polypeptide, which assembled into active GS isoenzymes constituting about 25% of the total GS activity. In in vitro plantlets of MIT-1, but not CYT-4, the novel polypeptide was found to be associated with the mitochondria. Moreover in MIT-1, the size of the novel polypeptide was not that predicted of the precursor (44.9 kDa) but was about 39 kDa, the same size as the authentic GS gamma polypeptide in CYT-4. These results are consistent with the precursor being imported into the mitochondria and cleaved near the fusion junction between the two sequences. These experiments have therefore shown that the presequence of the beta-F1 ATPase has successfully targeted the GS gamma polypeptide to the mitochondria of transgenic tobacco where it has assembled into an active isoenzyme. However, in fully regenerated plants growing photoautotrophically in growth-room conditions, although the constructs were still expressed, the gamma polypeptide did not accumulate to the same levels as in in vitro plantlets and new isoenzyme activities were now barely detectable. Moreover in leaves of the mature MIT-1 plants, the gamma polypeptide was found to be associated with the insoluble fraction of the mitochondria. The results of these experiments are discussed.
Plant Mol Biol 1990 Dec
PMID:Targeting of glutamine synthetase to the mitochondria of transgenic tobacco. 198 2

The URE2 gene of Saccharomyces cerevisiae has been cloned and sequenced. It encodes a predicted polypeptide of 354 amino acids with a molecular weight of 40,226. Deletion of the first 63 amino acids does not have any effect on the function of the protein. Studies with disruption alleles of the URE2 and GLN3 genes showed that both genes regulate GLN1 and GDH2, the structural genes for glutamine synthetase and NAD-linked glutamate dehydrogenase, respectively, at the transcriptional level, but expression of the regulatory genes does not appear to be regulated. Active URE2 gene product was required for the inactivation of glutamine synthetase upon addition of glutamine to cells growing with glutamate as the source of nitrogen. The predicted URE2 gene product has homology to glutathione S-transferases. The gene has been mapped to chromosome XIV, 5.9 map units from petX and 3.4 map units from kex2.
Mol Cell Biol 1991 Feb
PMID:The URE2 gene product of Saccharomyces cerevisiae plays an important role in the cellular response to the nitrogen source and has homology to glutathione s-transferases. 199 Feb 86

Two mouse glutamine synthetase (GSase) cDNAs were cloned that correspond to the 2.8 kb and 1.4 kb mRNA species found in many mouse tissues (1 kb = 10(3) base-pairs). There is a sequence homology of about 90% to other mammalian GSase cDNAs in the coding region. A 2.1 kb mRNA can be discerned in fat tissue, the most abundant source of GSase mRNA. Three genomic clones G4, G21 and G2 contain GSase sequences. By several criteria G21 and G2 are pseudogenes, while G4 is a functional gene composed of seven exons and six introns. Primer extension, RNase protection and Northern analysis provide evidence that all tissues use the same major RNA start site and the different-sized mRNAs are due to the usage of two different poly(A) sites, neither of which has the consensus AAUAAA sequence. When tested by transfection into Hep G2 human hepatoma cells the G4 promoter can produce correctly initiated mRNA with only 350 base-pairs of 5' regulatory sequences. A major interest in GSase expression is its restriction to pericentral hepatocytes in adult liver. In this paper we show by in situ hybridization that GSase mRNA is only found in glial cells in the adult brain and in proximal tubular epithelium of the kidney. Coupled with the earlier demonstration of expression of GSase only in pericentral hepatocytes, it is clear that this gene is regulated by position-specific signals in many cell types.
J Mol Biol 1989 Jul 05
PMID:Mouse glutamine synthetase is encoded by a single gene that can be expressed in a localized fashion. 247 38

We have obtained transgenic tobacco plants overexpressing the enzyme glutamine synthetase (GS) by fusing an alfalfa GS gene to the cauliflower mosaic virus 35S promotor and integrating it into Nicotiana tabacum var. W38 plants by Agrobacterium tumefaciens mediated gene transfer. The amount of RNA specific to alfalfa GS was about 10 times higher in transgenic tobacco plants than in alfalfa. The alfalfa GS produced by these transgenic plants was identified by Western blotting and represented 5% of total soluble protein in the transformed plants, amounting to a 5-fold increase in specific GS activity and in a 20-fold increase in resistance to the GS inhibitor L-phosphinothricin in vitro. Tissue from GS overproducing plants showed a sevenfold lower amount of free NH3. The amino acid composition of the plant tissue was not altered significantly by GS overproduction. GS overproducing plants were fertile and grew normally. These data show that a high level of expression of a key metabolic enzyme such as glutamine synthetase does not interfere with growth and fertility of plants.
Mol Gen Genet 1989 Jun
PMID:Overproduction of alfalfa glutamine synthetase in transgenic tobacco plants. 247 55

Glutaminase mRNA levels increased over 3-fold relative to total RNA, poly(A)+ RNA, and beta-actin mRNA in neonatal rat cerebellar granule cells as the cells differentiated between days 3 and 8 in culture. In contrast, mRNA levels of another glutamate cycle enzyme, glutamine synthetase, remained constant. Glutaminase protein levels increased per cell more than 2-fold between days 3 and 8, and at least 3-fold by day 10 in these cells. The total amount of glutamate per cell increased about 40% during this period. Glutaminase induction paralleled the development of Ca2+-dependent glutamate release, and the formation of neurites, synaptic vesicles, and synapses. The induction of glutaminase in developing granule cells is consistent with a special role for glutaminase in the synthesis of neurotransmitter glutamate.
Brain Res Mol Brain Res 1989 Jul
PMID:Developmental induction of glutaminase in primary cultures of cerebellar granule cells. 257 Mar 41

The GLN1 gene of Saccharomyces cerevisiae was cloned by complementation of a gln1 auxotroph. A GLN1-lacZ fusion was constructed to assay GLN1 promoter activity. beta-Galactosidase and glutamine synthetase expression in chromosomally integrated GLN1-lacZ fusion strains were co-regulated in response to a shift from glutamine to glutamate as the nitrogen source, purine limitation, and 3-aminotriazole-induced histidine starvation. Regulation of GLN1 expression by each of the three pathways occurred at the transcriptional level. Increased accumulation of GLN1 mRNA was observed within 5 min after a shift from glutamine to glutamate as the nitrogen source. After 5 min, GLN1 mRNA levels were constant. The level of GLN1 transcript was reduced by approximately 75% within 5 min following glutamine addition to the cells growing with glutamate as nitrogen source. This indicates that the GLN1 message is unstable and has a half-life of approximately 3 min. Deletion analysis indicated that the sequences required for GLN1 expression are located within approximately 350 bp upstream from the transcriptional initiation site.
Mol Gen Genet 1989 Jun
PMID:Three regulatory systems control expression of glutamine synthetase in Saccharomyces cerevisiae at the level of transcription. 257 Mar 48

Transcription of the Bacillus subtilis gene coding of glutamine synthetase (glnA) is regulated by the nitrogen source. The glnA gene lies in an operon in which it is preceded by an open reading frame with the potential to encode a polypeptide of approximately 16,000 Mr. We have now shown that this open reading frame is utilized in vivo, that its product (GlnR) acts as a diffusible, negative regulator of gln transcription, and that GlnR is likely to be a DNA-binding protein. Certain mutations in glnR, including a large, in-frame deletion and a start codon mutation, led to high-level constitutivity of the operon; other mutations caused low-level constitutivity. These latter mutations, which affected the C terminus of GlnR, seemed to disrupt response to the nitrogen source without eliminating the ability of GlnR to bind to DNA. Wild-type GlnR by itself, however, did not impose nitrogen-dependent regulation; such regulation also required the product of glnA. A model is presented in which glutamine synthetase monitors the availability of nitrogen and imposes negative regulation by interaction with or modification of GlnR.
J Mol Biol 1989 Nov 05
PMID:Regulation of Bacillus subtilis glutamine synthetase gene expression by the product of the glnR gene. 257 33


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