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Query: UNIPROT:P06889 (Mol)
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A gene, designated GS1, was identified by its association with a CpG island approximately 100 kb telomeric to the steroid sulfatase (STS) locus on the distal short arm of the human X chromosome. Both cDNA and genomic clones of the GS1 gene have been isolated and characterized. The cDNA clone detects a 2.3 kb transcript in human placenta and fibroblasts, and may encode a protein of 214 amino acid residues. Although sequences homologous to GS1 cDNA are present on chromosomes 1, 20, X, and Y, the functional GS1 gene is on the X chromosome. The GS1 gene appears to be non-essential, as there are no obvious clinical differences between STS deficient patients with point mutations in the STS gene, and patients with a deletion of the STS and GS1 genes. The GS1 gene is expressed from mouse-human cell hybrids containing active or inactive human X chromosomes, indicating that it escapes X inactivation. Characterization of GS1 genomic clones revealed that the gene consists of 4 exons spanning over 105 kb, with its transcriptional direction opposite to that of the STS gene. The isolation and characterization of a new gene which escapes X inactivation from distal Xp is of interest as it adds to our understanding of the structural organization of the human X chromosome and may help in providing clues regarding the mechanism of X-inactivation.
Hum Mol Genet 1992 Apr
PMID:Isolation of a new gene from the distal short arm of the human X chromosome that escapes X-inactivation. 128 67

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

Three structurally distinct cDNA clones for cytosolic glutamine synthetase (GS1) were isolated from libraries prepared from senescing radish cotyledons. Northern blot analysis showed that transcripts from two of the three genes encoding GS1, Gln1;1 and Gln1;3, accumulated in the cotyledons during both dark-induced and natural senescence. Transcripts from the last gene, Gln1;2, remained at a low level during both processes. Transcripts from all three Gln1 genes accumulated in cotyledons of germinating seeds. We infer from these findings that GS1 enzymes function in both germination and senescence to convert ammonium to glutamine to remobilize nitrogen from source to sink organs. We have also examined the pattern of expression of these genes in different tissues. All three genes are expressed in roots. A large amount of transcripts from Gln1;1 accumulated in hypocotyls. Whereas none were transcribed in flowers. During dark-induced senescence of cotyledons, application of inorganic nitrogen delayed chlorophyll degradation. Inorganic nitrogen enhanced the accumulation of Gln1;1 transcripts, but decreased those of Gln1;3. In contrast, application of glutamine promoted yellowing of cotyledons during the dark treatment, and slightly increased the amounts of transcripts from Gln1;3 but decreased those of Gln1;1. Transcription of the three Gln1 genes appears, therefore, to be differentially regulated in radish cotyledons during senescence and germination.
Plant Mol Biol 1994 Dec
PMID:Biphasic and differential expression of cytosolic glutamine synthetase genes of radish during seed germination and senescence of cotyledons. 785 19

The responses of the five cytosolic-type glutamine synthetase (GS1) genes of maize to treatment of hydroponically grown seedlings with 10 mM KNO3 or 10 mM NH4Cl were analyzed. Non-coding 3' gene-specific hybridization probes and radioanalytic imaging were used to quantitate individual gene transcript levels in excised roots and shoots before treatment and at selected times after treatment. Genes GS1-1 and GS1-2 exhibited distinct organ-specific responses to treatment with either nitrogen source. The GS1-1 transcript level increased over three-fold in roots, but changed little if any in shoots. In contrast, the GS1-2 transcript level increased over two-fold in shoots, but decreased in roots after treatment. Increased transcript levels were evident at 4 h after treatment with either nitrogen source, with maximum accumulations present at 8 h after treatment with ammonium and at 10-12 h after treatment with nitrate. The GS1-3 gene transcript level showed little or no change after treatment with either nitrogen source. The GS1-4 gene transcript level remained constant in shoots of treated seedlings, whereas in roots, it exhibited relatively minor, but complex responses to these two nitrogen sources. The GS1-5 gene transcript is present in very small amounts in seedlings, making it difficult to analyze its response to metabolites in young plants. These results provide support for the possibility that different cytosolic GS genes of maize play distinct roles in nitrogen metabolism during plant growth and differentiation.
Plant Mol Biol 1994 Dec
PMID:Root- and shoot-specific responses of individual glutamine synthetase genes of maize to nitrate and ammonium. 785 28

A glutamine synthetase (GS) cDNA isolated from an alfalfa cell culture cDNA library was found to represent a cytoplasmic GS. The full-length alfalfa GS1 coding sequence, in both sense and antisense orientation and under the transcriptional control of the cauliflower mosaic virus 35S promoter, was introduced into tobacco. Leaves of tobacco plants transformed with the sense construct contained greatly elevated levels of GS transcript and GS polypeptide which assembled into active enzyme. Leaves of the plants transformed with the antisense GS1 construct showed a significant decrease in the level of both GS1 and GS2 polypeptides and GS activity, but did not show any significant decrease in the level of endogenous GS mRNA. We have proposed that antisense inhibition using a heterologous antisense GS RNA occurs at the level of translation. Our results also suggest that the post-translational assembly of GS subunits into a holoenzyme requires an additional factor(s) and is under regulatory control.
Mol Gen Genet 1993 Jan
PMID:Modulation of glutamine synthetase gene expression in tobacco by the introduction of an alfalfa glutamine synthetase gene in sense and antisense orientation: molecular and biochemical analysis. 809 85

A full-length cDNA clone (pGSP114) encoding glutamine synthetase was isolated from a lambda gt11 library of the gymnosperm Pinus sylvestris. Nucleotide sequence analysis showed that pGSP114 contains an open reading frame encoding a protein of 357 amino acid residues with a calculated molecular mass of 39.5 kDa. The derived amino acid sequence was more homologous to cytosolic (GS1) (78-82%) than to chloroplastic (GS2) (71-75%) glutamine synthetase in angiosperms. The lack of N-terminal presequence and C-terminal extension which define the primary structure of GS2, also supports that the isolated cDNA encodes cytosolic GS. Southern blot analysis of genomic DNA from P. sylvestris and P. pinaster suggests that GS may be encoded by a small gene family in pine. GS mRNA was more abundant in cotyledons and stems than in roots of both Scots and maritime pines. Western blot analysis in P. sylvestris seedlings showed that only one GS polypeptide, similar in size to GS1 in P. pinaster, could be detected in several different tissues. Our results suggest that cytosolic GS is mainly responsible for glutamine biosynthesis in pine seedlings.
Plant Mol Biol 1993 Aug
PMID:Molecular characterization of a cDNA clone encoding glutamine synthetase from a gymnosperm, Pinus sylvestris. 810 6

The maize genome has been shown to contain six glutamine synthetase (GS) genes with at least four different expression patterns. Noncoding 3' gene-specific probes were constructed from all six GS cDNA clones and used to examine transcript levels in selected organs by RNA gel blot hybridization experiments. The transcript of the single putative chloroplastic GS2 gene was found to accumulate primarily in green tissues, whereas the transcripts of the five putative GS1 genes were shown to accumulate preferentially in roots. The specific patterns of transcript accumulation were quite distinct for the five GS1 genes, with the exception of two closely related genes.
Plant Mol Biol 1993 Oct
PMID:Differential expression of six glutamine synthetase genes in Zea mays. 810 13

In maize, a small multigene family encodes the cytosolic isoforms of glutamine synthetase (GS), and five cDNAs, designated pGS1a, pGS1b, pGS1c, pGS1d, and pGS1e, have been cloned (Sakakibara, H., Kawabata, S., Takahashi, H., Hase, T., and Sugiyama, T. (1992) Plant Cell Physiol. 33, 49-58; Li, M., Villemur, R., Hussey, P. J., Silflow, C. D., Gantt, J. S., and Snustad, D. P. (1993) Plant Mol. Biol. 23, 401-407). This report describes the identification and enzymatic characterization of the cytosolic isoforms of GS in maize roots, namely GS1 and GSr. The purified isoforms, as well as recombinant enzymes that had been overexpressed in Escherichia coli, were analyzed by capillary liquid chromatography/electrospray ionization-mass spectrometry, and GS1 and GSr were identified as the products of the GS1a/GS1b and GS1c/GS1d genes, respectively. Upon the addition of ammonia to the culture medium, significant amounts of GSr accumulated and a preferential increase in GS synthetase activity, as compared to GS transferase activity, was found in the root extract. Assays with the purified recombinant enzymes confirmed that the specific biosynthetic and synthetase activities of GSr were 1.6-fold higher than those of GS1. Marked differences in stability were also found between the two isoforms: GSr was more sensitive to heat than GS1 and octameric aggregates of the subunits of GSr were easily dissociated to monomers than those of GS1 at low concentrations of Mn2+ and Mg2+ ions. These characteristics of the ammonia-induced isoform of GS seem to be physiologically important for the primary assimilation of external ammonia by roots.
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PMID:Molecular identification and characterization of cytosolic isoforms of glutamine synthetase in maize roots. 893 84

Glutamine synthetase (GS) catalyzes the ATP-dependent condensation of NH3 with glutamate to produce glutamine. In plants GS is an octameric enzyme and is located either in the cytoplasm (GS1) or in the chloroplast (GS2). Two distinct classes of GS1 genes with unique 3'-untranslated region (3'UTR) have been identified in alfalfa. We have demonstrated that the two classes exhibit differential expression pattern in the different plant organs suggesting different functional roles for the different isozymes. To determine the functional significance of the two classes of GS1 genes in alfalfa, we have utilized antisense gene constructs aimed specifically at the 3'UTR of the two GS1 genes and introduced them individually into alfalfa. Our data show that the gene constructs are effective in lowering the corresponding transcript level very effectively though there were organ-specific differences in the level of reduction. No transcript corresponding to the antisense gene construct was detected in any of the alfalfa transformants though they accumulated to significant levels in transgenic tobacco containing the same construct. This suggests that the antisense transcript was not stable in the presence of the homologous target sequence. Transgenic alfalfa with up to 80% reduction in the transcript level corresponding to each gene class, however, showed no reduction in GS activity or GS1 polypeptide level. The results suggest that GS1 mRNA levels are not rate-limiting for GS1 polypeptide synthesis and that GS levels are controlled both at the transcriptional and translational/post-translational level.
Plant Mol Biol 1998 Jun
PMID:Down-regulation of specific members of the glutamine synthetase gene family in alfalfa by antisense RNA technology. 961 20

The expression of a cytosolic glutamine synthetase (GS1; EC 6.3.1.2) gene was examined in cotyledons of Scots pine seedlings. Light strongly stimulated GS1 mRNA accumulation during development. Similarly, steady-state levels of GS1 transcripts increased in dark-grown seedlings transferred to light and decreased in dark-adapted seedlings. Light/dark adaptation affected rbcS and lhcb2 mRNA levels and chlorophyll contents in the same manner. Light-grown seedlings in the presence of the herbicide norflurazon showed a drastic decrease in mRNA for GS and photosynthetic proteins, whereas the effect of the herbicide on mitochondrial beta-ATP synthase mRNA was limited. These results indicate that factors associated with developing chloroplasts could be required for maximal GS1 gene expression during seedling development. The level of GS polypeptide, determined by immunoblot, was up-regulated during seedling development in the light or dark. However, the levels of the polypeptide detected were unaltered by the light/dark adaptation treatments. The analysis of GS1 mRNA association with polysomes indicated that the discrepancies between GS protein and mRNA levels are not a result of a differential translational rate of the transcript in darkness relative to light. Two GS isoproteins with different isoelectric point were resolved by two-dimensional PAGE in light- and dark-germinated plants. The relative abundance of one of them was markedly affected by light and correlated with the observed changes in GS mRNA, suggesting that the other form is not a product derived from the detected transcript. In situ hybridization of cotyledon sections showed the presence of GS1 mRNAs in mesophyll and phloem cells confirming gene expression in photosynthetic tissues. High levels of transcript were detected also in meristematic cells of apical primordia. These data suggest a dual role for the GS1 gene associated with chloroplast development/activity and glutamine biosynthesis for nitrogen mobilization during early growth of Scots pine.
Plant Mol Biol 1999 Jul
PMID:Expression analysis of a cytosolic glutamine synthetase gene in cotyledons of Scots pine seedlings: developmental, light regulation and spatial distribution of specific transcripts. 1048 Mar 86


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