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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Synechocystis sp. PCC 6803 glutamine synthetase type I (GS) activity is controlled by direct interaction with two inactivating factors (IF7 and IF17). IF7 and IF17 are homologous polypeptides encoded by the gifA and gifB genes respectively. We investigated the transcriptional regulation of these genes. Expression of both genes is maximum in the presence of ammonium, when GS is inactivated. Nitrogen starvation attenuates the ammonium-mediated induction of gifA and gifB as well as the ammonium-mediated inactivation of GS. Putative binding sites for the transcription factor NtcA were identified at -7.5 and -30.5 bp upstream of gifB and gifA transcription start points respectively. Synechocystis NtcA protein binding to both promoters was demonstrated by gel electrophoresis mobility shift assays. Constitutive high expression levels of both genes were found in a Synechocystis NtcA non-segregated mutant (SNC1), which showed a fourfold reduction in the ntcA expression. These experiments indicate a repressive role for NtcA on the transcription of gifA and gifB genes. Our results demonstrate that NtcA plays a central role in GS regulation in cyanobacteria, stimulating transcription of the glnA gene (GS structural gene) and suppressing transcription of the GS inactivating factor genes gifA and gifB.
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PMID:NtcA represses transcription of gifA and gifB, genes that encode inhibitors of glutamine synthetase type I from Synechocystis sp. PCC 6803. 1071 99

The gene encoding the ferredoxin-dependent glutamate synthase (Fd-GOGAT), glsF, from the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120, has been cloned and sequenced. Unlike other cyanobacteria, Anabaena 7120 contains only Fd-GOGAT, lacking NADH-GOGAT. The amount of glsF transcript and Fd-GOGAT activity were similar under all the nitrogen growth conditions tested. Enzyme activity, Western and Northern blot analyses indicated that Fd-GOGAT is absent in the heterocysts, while glutamine synthetase (GS) and NADP-isocitrate dehydrogenase (IDH) were present in these specialised cells. Our results clearly indicate that the GS-GOGAT pathway is not operative in the heterocysts, and hence glutamate must be imported from the adjacent vegetative cells, to sustain GS activity. Heterocysts probably export glutamine or another nitrogen rich compound like arginine to the vegetative cells.
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PMID:The GS-GOGAT pathway is not operative in the heterocysts. Cloning and expression of glsF gene from the cyanobacterium Anabaena sp. PCC 7120. 1091 29

We report the cloning and sequencing of the glnN gene encoding a class III glutamine synthetase from the cyanobacterium Synechococcus strain PCC 7942. Mapping of the transcriptional start site revealed a DNA sequence in the promoter region that resembles an imperfect NtcA binding motif. Expression of glnN is impaired in NtcA- and P(II)-deficient mutants. The only parameter which was negatively affected in the glnN mutant compared to the wild type was the recovery rate of prolonged nitrogen-starved cells with low concentrations of combined nitrogen.
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PMID:The Synechococcus strain PCC 7942 glnN product (glutamine synthetase III) helps recovery from prolonged nitrogen chlorosis. 1098 71

The expression of sll1689, an open reading frame from the cyanobacterium Synechocystis sp. strain PCC 6803 putatively encoding a member of the sigma(70) family of sigma factors, appears to be regulated by the nitrogen control transcription factor NtcA. Disruption of sll1689 had no noticeable effect on exponential growth, identifying its product as a member of the group 2, nonessential class of sigma(70)-like sigma factors; however, this disruption decreased the viability of the cells after long periods of nitrogen starvation. We have named this gene rpoD2-V. The expression of glnN, encoding a type III glutamine synthetase, was impaired in strains bearing an inactivated copy of the rpoD2-V gene.
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PMID:Nitrogen-regulated group 2 sigma factor from Synechocystis sp. strain PCC 6803 involved in survival under nitrogen stress. 1120 9

The physiological regulation of glutamine synthetase (GS; EC 6.3.1.2) in the axenic Prochlorococcus sp. strain PCC 9511 was studied. GS activity and antigen concentration were measured using the transferase and biosynthetic assays and the electroimmunoassay, respectively. GS activity decreased when cells were subjected to nitrogen starvation or cultured with oxidized nitrogen sources, which proved to be nonusable for Prochlorococcus growth. The GS activity in cultures subjected to long-term phosphorus starvation was lower than that in equivalent nitrogen-starved cultures. Azaserine, an inhibitor of glutamate synthase, provoked an increase in enzymatic activity, suggesting that glutamine is not involved in GS regulation. Darkness did not affect GS activity significantly, while the addition of diuron provoked GS inactivation. GS protein determination showed that azaserine induces an increase in the concentration of the enzyme. The unusual responses to darkness and nitrogen starvation could reflect adaptation mechanisms of Prochlorococcus for coping with a light- and nutrient-limited environment.
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PMID:In vivo regulation of glutamine synthetase activity in the marine chlorophyll b-containing cyanobacterium Prochlorococcus sp. strain PCC 9511 (oxyphotobacteria). 1131 1

The regulatory circuits that control nitrogen metabolism are relatively well known in several bacterial model groups. However, much less is understood about how the nitrogen status of the cell is perceived in vivo. In cyanobacteria, the transcription factor NtcA is required for regulation (activation or repression) of an extensive number of genes involved in nitrogen metabolism. In contrast, how NtcA activity is regulated is largely unknown. Assimilation of ammonium by most microorganisms occurs through the sequential action of two enzymes: glutamine synthetase (GS) and glutamate synthase. Interestingly, regulation of the expression of NtcA-dependent genes in the cyanobacterium Synechocystis sp. PCC 6803 is altered in mutants with modified levels of GS activity. Two types of mutants were analyzed: glnA null mutants that lack GS type I and gif mutants unable to inactivate GS in the presence of ammonium. Changes in the intracellular pools of 19 different amino acids and the keto acid 2-oxoglutarate were recorded in wild-type and mutant strains under different nitrogen conditions. Our data strongly indicate that the nitrogen status in cyanobacteria is perceived as changes in the intracellular 2-oxoglutarate pool.
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PMID:Cyanobacteria perceive nitrogen status by sensing intracellular 2-oxoglutarate levels. 1147 9

The inactivation of glutamine synthetase (GS; EC 6.3.1.2) by metal-catalyzed oxidation (MCO) systems was studied in several Prochlorococcus strains, including the axenic PCC 9511. GS was inactivated in the presence of various oxidative systems, either enzymatic (as NAD(P)H+NAD(P)H-oxidase+Fe(3+)+O(2)) or non-enzymatic (as ascorbate+Fe(3+)+O(2)). This process required the presence of oxygen and a metal cation, and is prevented under anaerobic conditions. Catalase and peroxidase, but not superoxide dismutase, effectively protected the enzyme against inactivation, suggesting that hydrogen peroxide mediates this mechanism, although it is not directly responsible for the reaction. Addition of azide (an inhibitor of both catalase and peroxidase) to the MCO systems enhanced the inactivation. Different thiols induced the inactivation of the enzyme, even in the absence of added metals. However, this inactivation could not be reverted by addition of strong oxidants, as hydrogen peroxide or oxidized glutathione. After studying the effect of addition of the physiological substrates and products of GS on the inactivation mechanism, we could detect a protective effect in the case of inorganic phosphate and glutamine. Immunochemical determinations showed that the concentration of GS protein significantly decreased by effect of the MCO systems, indicating that inactivation precedes the degradation of the enzyme.
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PMID:Regulation of glutamine synthetase by metal-catalyzed oxidative modification in the marine oxyphotobacterium Prochlorococcus. 1178 30

The transcription factor NtcA is a global regulator of nitrogen homeostasis in cyanobacteria. It thus positively regulates the expression of genes related to nitrogen assimilation such as glnA (which encodes glutamine synthetase) and ntcA itself in response to nitrogen shortage or depletion. The binding of NtcA to the glnA and ntcA promoters of Synechococcus sp. PCC 7942 in vitro now has been shown to be enhanced by 2-oxoglutarate. In vitro analysis of gene transcription also revealed that the interaction of NtcA with its promoter element was not sufficient for activation of transcription, and 2-oxoglutarate was required for transcriptional initiation by NtcA. Given that the intracellular concentration of 2-oxoglutarate is inversely related to nitrogen availability, it is proposed that this metabolite functions as a signaling molecule that transmits information on cellular nitrogen status to NtcA and thereby regulates the transcription of genes related to nitrogen assimilation in cyanobacteria.
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PMID:Transcriptional activation of NtcA-dependent promoters of Synechococcus sp. PCC 7942 by 2-oxoglutarate in vitro. 1191 35

Synechocystis sp. PCC 6803 mutants, in which one of the eukaryotic-type serine/threonine protein kinase genes pknD, pknE, pknG, and pknH was inactivated, were obtained by insertion mutagenesis. None of these mutants differed phenotypically from the wild-type strain, indicating that the pknD, pknE, pknG, and pknH genes are not of crucial importance for the photoautotrophically grown cyanobacterium. Mutant with the inactivated pknE gene was resistant to L-methionine-D,L-sulfoximine and especially to methylamine. The resistance was neither due to the impaired transport of these compounds nor to the inhibition of the production of toxic gamma-glutamylmethylamide from methylamine. The data presented suggest that resistance to methylamine may be associated with alterations in the regulation of the glutamine synthetase system and that the PknE protein kinase may be involved in the regulation of nitrogen metabolism in the cyanobacterium studied.
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PMID:[Insertional inactivation of genes encoding eukaryotic type serine/threonine protein kinases in cyanobacterium Synechocystis sp. PCC 6803]. 1269 94

The regulation of glutamine synthetase (EC 6.3.1.2) from Prochlorococcus was previously shown to exhibit unusual features: it is not upregulated by nitrogen starvation and it is not inactivated by darkness (El Alaoui et al. (2001) Appl Environ Microbiol 67: 2202-2207). These are probably caused by adaptations to oligotrophic environments, as confirmed in this work by the marked decrease in the enzymatic activity when cultures were subjected to iron or phosphorus starvation. In order to further understand the adaptive features of ammonium assimilation in this cyanobacterium, glutamine synthetase was purified from two Prochlorococcus strains: PCC 9511 (high-light adapted) and SS120 (low-light adapted). We obtained approximately 100-fold purified samples of glutamine synthetase electrophoretically homogeneous, with a yield of approximately 30%. The estimated molecular mass of the subunits was roughly the same for both strains: 48.3 kDa. The apparent Km constants for the biosynthetic activity were 0.30 mM for ammonium, 1.29 mM for glutamate and 1.35 mM for ATP; the optimum pH was 8.0. Optimal temperature was surprisingly high (55 degrees C). Phylogenetic analysis of glnA from three Prochlorococcus strains (MED4, MIT9313 and SS120) showed they group closely with marine Synechococcus isolates, in good agreement with other studies based on 16 S RNA sequences. All of our results suggest that the structure and kinetics of glutamine synthetase in Prochlorococcus have not been significantly modified during the evolution within the cyanobacterial radiation, in sharp contrast with its regulatory properties.
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PMID:Glutamine synthetase from the marine cyanobacteria Prochlorococcus spp: characterization, phylogeny and response to nutrient limitation. 1271 67


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