Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glutamine synthetase catalyzes the formation of glutamine from glutamate and ammonia. It plays a central role in both amino acid neurotransmitter metabolism and ammonia detoxification in the central nervous system. Glutamine synthetase expression is regulated in developmental, hormonal, and in tissue- and cell-specific manners. We have cloned a full-length cDNA coding for rat glutamine synthetase, and have found an AT-rich area of conservation in the 3' untranslated regions between rat, mouse, and chicken, which may play a part in the regulation of the stability of the glutamine synthetase message. We have also cloned and mapped the gene coding for rat glutamine synthetase, and identified, by sequence analysis, areas potentially important for the regulation of glutamine synthetase transcription. Transient transfection of a variety of cell lines with deletion constructs of the glutamine synthetase promoter driving a chloramphenicol acetyltransferase reporter gene functionally demonstrates regions of the promoter containing elements important for transcriptional regulation.
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PMID:Cloning and functional characterization of the rat glutamine synthetase gene. 167 54

The cis-acting element mediating glucocorticoid inducibility of the chicken glutamine synthetase gene has been identified. Transfection studies using intact embryonic chicken retinae and L6 myoblasts demonstrate that sequences located between 1,849 and 2,120 nucleotides upstream of the glutamine synthetase transcription start site are required to achieve hormonally inducible expression of the chloramphenicol acetyltransferase gene. Moreover, a 42-nucleotide fragment from this region provides a robust hormonal induction when positioned approximately 2 kilobases from the SV40 early promoter. A sequence containing 8 nucleotides in common with the 12-nucleotide consensus glucocorticoid response element is encoded within this element. DNase I footprinting experiments confirm that this consensus sequence provides the only binding sites for the glucocorticoid receptor within the DNA required for inducibility. Removal of 8 nucleotides that map outside of the footprinting region results in attenuation of the hormonal response in L6 myoblasts and abolition of the response in embryonic retinae. This deletion eliminates the sequence 5'CAGCGTCA3', a sequence that resembles the canonical cyclic AMP response element (CRE), activating transcription factor (ATF), and AP1 binding sites. These results suggest that the glucocorticoid receptor acts in collaboration with a member of the jun/fos/ATF/CREB family of transcription factors to mediate a strong glucocorticoid induction at a site 2.1 kilobases upstream of the glutamine synthetase transcription start site.
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PMID:A single upstream glucocorticoid response element juxtaposed to an AP1/ATF/CRE-like site renders the chicken glutamine synthetase gene hormonally inducible in transfected retina. 168 91

In this communication we demonstrate that gene transfer methodology can be applied to study gene expression in intact retinal explant cultures. The appropriate enzyme activity is observed in extracts obtained after electroporation of embryonic day-10 chicken retina with plasmids containing the chloramphenicol acetyltransferase-encoding or beta-galactosidase-encoding reporter genes under transcriptional control by the Rous sarcoma virus long terminal repeat. Similar results are obtained using Ca.phosphate-mediated gene transfer. Moreover, it has been previously established that glucocorticoid hormones stimulate transcription of glutamine synthetase (Glns) mRNA in embryonic retina. We report here that, based on the results of gene transfer experiments with chimeric plasmids containing 5'-flanking DNA derived from the cloned chicken Glns-encoding gene (Glns), essential glucocorticoid response elements reside between approx. 1.3 kb and 2.5 kb upstream from the Glns transcription start point. These data show that transfection of explant cultures can provide a useful approach to the study of gene expression in complex systems.
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PMID:Glucocorticoid-inducible expression of a glutamine synthetase-CAT-encoding fusion plasmid after transfection of intact chicken retinal explant cultures. 197 78

Nine different proteins were imported into isolated pea chloroplasts in vitro. For seven of these [the large and small subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), beta-subunit of ATP synthase, glutamine synthetase, the light-harvesting chlorophyll a/b binding protein, chloramphenicol acetyltransferase, and pre-beta-lactamase], a fraction was found to migrate as a stable high-molecular-weight complex during nondenaturing gel electrophoresis. This complex contained the mature forms of the imported proteins and the groEL-related chloroplast chaperonin 60 (previously known as Rubisco subunit binding protein). Thus, the stable association of imported proteins with this molecular chaperone is widespread and not necessarily restricted to Rubisco subunits or to chloroplast proteins. With two of the imported proteins (ferredoxin and superoxide dismutase), such complexes were not observed. It seems likely that, in addition to its proposed role in assembly of Rubisco, the chloroplast chaperonin 60 is involved in the assembly or folding of a wide range of proteins in chloroplasts.
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PMID:Several proteins imported into chloroplasts form stable complexes with the GroEL-related chloroplast molecular chaperone. 257 24

In previous studies of the glutamine synthetase gene, the promoter and two enhancer elements, one in the upstream region and one within the first intron, were identified. To analyze the role of the far-upstream enhancer element in the regulation of the expression of the glutamine synthetase gene, two classes of transgenic mice were generated. In GSK mice, the basal promoter directs the expression of the chloramphenicol acetyltransferase reporter gene. In GSL mice reporter gene expression is driven, in addition, by the upstream regulatory region, including the far-upstream enhancer. Whereas chloramphenicol acetyltransferase expression was barely detectable in GSK mice, high levels were detected in GSL mice. By comparing chloramphenicol acetyltransferase expression with that of endogenous glutamine synthetase in GSL mice, three groups of organs were distinguished in which the effects of the upstream regulatory region on the expression of glutamine synthetase were quantitatively different. The chloramphenicol acetyltransferase mRNA in the GSL mice was shown to be localized in the pericentral hepatocytes of the liver. The developmental changes in chloramphenicol acetyltransferase enzyme activity in the liver were similar to those in endogenous glutamine synthetase. These results show that the upstream region is a major determinant for three characteristics of glutamine synthetase expression: its organ specificity, its pericentral expression pattern in the liver, and its developmental appearance in the liver.
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PMID:The spatio-temporal control of the expression of glutamine synthetase in the liver is mediated by its 5'-enhancer. 749 22

A new glutamine synthetase gene, glnN, which encodes a polypeptide of 724 amino acid residues (M(r), 79,416), has been identified in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803; this is the second gene that encodes a glutamine synthetase (GS) in this cyanobacterium. The functionality of this gene was evidenced by its ability to complement an Escherichia coli glnA mutant and to support Synechocystis growth in a strain whose glnA gene was inactivated by insertional mutagenesis. In this mutant (strain SJCR3), as well as in the wild-type strain, the second GS activity was subject to regulation by the nitrogen source, being strongly enhanced in nitrogen-free medium. Transcriptional fusion of a chloramphenicol acetyltransferase (cat) gene with the 5'-upstream region of glnN suggested that synthesis of the second Synechocystis GS is regulated at the transcriptional level. Furthermore, the level of glnN mRNA, a transcript of about 2,300 bases, was found to be strongly increased in nitrogen-free medium. The glnN product is similar to the GS subunits of Bacteroides fragilis and Butyrivibrio fibrisolvens, two obligate anaerobic bacteria whose GSs are markedly different from other prokaryotic and eukaryotic GSs. However, significant similarity is evident in the five regions which are homologous in all of the GSs so far described. The new GS gene was also found in other cyanobacteria but not in N2-fixing filamentous species.
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PMID:A new type of glutamine synthetase in cyanobacteria: the protein encoded by the glnN gene supports nitrogen assimilation in Synechocystis sp. strain PCC 6803. 790 87

The glucocorticoid receptor in chicken embryonic neural retina is expressed early in ontogeny, yet the tissue's response to the glucocorticoid hormone, i.e., induction of glutamine synthetase (GS), develops later, only during week 2 of ontogeny. Transient transfection of embryonic day 7 (E7) retinal cells, which are nonresponsive to glucocorticoids, with chimeric plasmids containing the chloramphenicol acetyltransferase reporter gene under the control of glucocorticoid-responsive promoters demonstrated that GR in E7 cells is a functional transactivating factor. We show that the limiting transcription factor that controls the developmental acquisition of responsiveness to glucocorticoids is similar to a CCAAT enhancer-binding protein (C/EBP). This protein recognizes a sequence in the promoter of the chick GS gene, which is required for eliciting the glucocorticoid response. Retinal C/EBP-like protein was not detected in the glucocorticoid-nonresponsive (E7) proliferating glioblasts but was found to be present in the glucocorticoid-responsive (E12) postmitotic cells. Premature expression of C/EBP in the nonresponsive E7 cells by transfection was shown to enhance the developmental acquisition of responsiveness to the glucocorticoid hormone, as deduced from the level of GS inducibility.
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PMID:Involvement of a C/EBP-like protein in the acquisition of responsiveness to glucocorticoid hormones during chick neural retina development. 809 26

In chicken embryo retina, competence for induction of the glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming); EC 6.3.1.2] gene by glucocorticoid hormones increases progressively with development; this competence is minimal in 6-day retina (E6) and high by day 10 (E10). Because the level of glucocorticoid receptors (GRs) in the retina does not increase during that time, we investigated whether the transcriptional activity of GR increased between days 6 and 10 of development. The glucocorticoid-inducible chloramphenicol acetyltransferase (CAT) constructs 2GRE-37TK and p delta G46TCO, which contain glucocorticoid-responsive elements attached to a TATA box and to the thymidine kinase promoter, respectively, were transfected into E6 and E10 retinas, and their inducibility was examined. CAT expression could be induced in the transfected E10 retina but was not induced in the transfected E6 retina. However, induction was obtained also in E6 retina after cotransfection with a GR expression vector. Noninducible CAT constructs (pRSV-CAT, pSV2CAT, and pBLCAT2) were expressed at both ages at similar levels. The CAT construct pGS2.1CAT, which is controlled by the upstream sequence of the chicken glutamine synthetase gene, could be induced in E10 retina but was not induced in E6 retina; however, cotransfection with the GR expression vector resulted in induction of pGS2.1CAT also in E6 retina. We interpret these results as showing that the transcriptional activity of GR in embryonic retina is developmentally controlled and suggest that its increase is causally implicated in the development of competence for glutamine synthetase induction.
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PMID:Developmental control of glucocorticoid receptor transcriptional activity in embryonic retina. 809 46

This report establishes that increasing the activity of cyclic AMP-dependent protein kinase (protein kinase A; PKA) potentiates glucocorticoid-mediated signaling in embryonic day 5.5 (E5.5) chicken retina. Expression of a glutamine synthetase-chloramphenicol acetyltransferase (CAT) fusion gene is not induced by treatment with glucocorticoid hormone in transfected E5.5 retina. However, treatment of the retina with forskolin, an activator of adenyl cyclase, or cotransfection with an expression vector encoding PKA is sufficient to render the fusion gene hormonally responsive. Similar results are obtained after forskolin treatment of E5.5 retina that have been transfected with a plasmid that contains the CAT reporter gene under transcriptional control by the thymidine kinase promoter and a 46-nucleotide enhancer with two glucocorticoid response elements (GREs). In contrast, forskolin augments but is not required to achieve glucocorticoid-inducible CAT gene expression in E5.5 retina transfected with a plasmid that contains the reporter driven by a minimal promoter with six juxtaposed GREs. Based on these results, we postulate that E5.5 retina contain glucocorticoid receptors whose signal transduction properties are enhanced by PKA. Unlike the transiently expressed glutamine synthetase fusion gene, however, activation of PKA does not render the endogenous glutamine synthetase gene glucocorticoid-inducible. Thus, its expression appears to be subject to an additional level of control in the developing retina.
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PMID:Protein kinase A activation of glucocorticoid-mediated signaling in the developing retina. 809 80

The differential response of the tyrosine aminotransferase (TAT) gene to glucocorticoids and insulin in HTC cells and cell clones derived from Reuber H35 cells (FaO and Fu5.5) have been analyzed by nuclear run-on assay. It has been previously shown that clones of cells from HTC and Reuber H35 cell lines, exhibit different sensitivities for the induction of TAT mRNA and enzyme activity. The purpose of the present study was to determine whether this difference in TAT expression between hepatocytes and hepatoma cell lines occurs at the level of TAT gene transcription or mRNA stability. A study of the TAT mRNA accumulation in all cell types showed that TAT mRNA in the Reuber H35 cell clones and hepatocytes was synthesized at a higher rate than in HTC cells. However, dexamethasone induction of alpha 1 AGP mRNA and glutamine synthetase was comparable to glucocorticoid bound receptors. In addition, cycloheximide decreased the rate at which induced levels of TAT mRNA were degraded. We also show that a heterologous fusion gene constructed from 3.0 kilobases (kb) 5' to the transcription initiation site of the rat TAT gene and the bacterial chloramphenicol acetyltransferase gene (CAT) responds similarly to dexamethasone in Fu5.5 and HTC cells as determined by transient transfection assay; and insulin inhibits dexamethasone mediated transcription in Reuber H35 cells and primary adult hepatocytes. These data indicate that DNA sequences involved in the differential response of the TAT gene to hormone treatments between HTC and Reuber H35 cell lines are not located in the first 3.0 kb fragment.
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PMID:Differential expression of tyrosine aminotransferase by glucocorticoids and insulin. 809 30


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