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  • 1
    Electronic Resource
    Electronic Resource
    NtcA represses transcription of gifA and gifB, genes that encode inhibitors of glutamine synthetase type I from Synechocystis sp. PCC 6803 (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01789.x
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  • 2
    Electronic Resource
    Electronic Resource
    A two-component signal transduction system involved in nickel sensing in the cyanobacterium Synechocystis sp. PCC 6803 (2002)
    Oxford, UK : Blackwell Science Ltd.
    Molecular microbiology 43 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In the cyanobacterium Synechocystis sp. PCC 6803, genes for Ni2+, Co2+, and Zn2+ resistance are grouped in a 12 kb gene cluster. The nrsBACD operon is composed of four genes, which encode proteins involved in Ni2+ resistance. Upstream from nrsBACD, and in opposite orientation, a transcription unit formed by the two genes rppA and rppB has been reported previously to encode a two-component signal transduction system involved in redox sensing. In this report, we demonstrate that rppA and rppB (here redesigned nrsR and nrsS respectively) control the Ni2+-dependent induction of the nrsBACD operon and are involved in Ni2+ sensing. Thus, expression of the nrsBACD operon was not induced by Ni2+ in a nrsRS mutant strain. Furthermore, nrsRS mutant cells showed reduced tolerance to Ni2+. Whereas the nrsBACD operon is transcribed from two different promoters, one constitutive and the other dependent on the presence of Ni2+ in the medium, the nrsRS operon is transcribed from a single Ni2+-inducible promoter. The nrsRS promoter is silent in a nrsRS mutant background suggesting that the system is autoregulated. Purified full length NrsR protein is unable to bind to the nrsBACD-nrsRS intergenic region; however, an amino-terminal truncated protein that contains the DNA binding domain of NrsR binds specifically to this region. Our nrsRS mutant, which carries a deletion of most of the nrsR gene and part of the nrsS gene, does not show redox imbalance or photosynthetic gene mis-expression, contrasting with the previously reported nrsR mutant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.02741.x
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  • 3
    Electronic Resource
    Electronic Resource
    Nitrogen control of the glnN gene that codes for GS type III, the only glutamine synthetase in the cyanobacterium Pseudanabaena sp. PCC 6903 (1998)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 30 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pseudanabaena sp. strain PCC 6903 is the first cyanobacteria lacking the typical prokaryotic glutamine synthetase type I encoded by the glnA gene. The glnN gene product, glutamine synthetase type III, is the only glutamine synthetase activity present in this cyanobacterium. Analysis of glnN expression clearly indicated a nitrogen-dependent regulation. Pseudanabaena glnN gene expression and GSIII activity were upregulated under nitrogen starvation or using nitrate as a nitrogen source, while low levels of transcript and activity were found in ammonium-containing medium. Primer extension analysis showed that the glnN gene promoter structure resembled that of the NtcA-related promoters. Mobility shift assays demonstrated that Synechocystis sp. PCC 6803 NtcA protein, expressed and purified from Escherichia coli , bound to the promoter of the Pseudanabaena 6903 glnN gene. The NtcA control of the glnN gene in this cyanobacterium suggested that, in the absence of a glnA gene, NtcA took control of the only glutamine synthetase gene in a fashion similar to the way the glnA gene is governed in those cyanobacteria harbouring a glnA gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.01143.x
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  • 4
    Electronic Resource
    Electronic Resource
    Utilization of nitrate, nitrite and ammonium by Chlamydomonas reinhardii (1983)
    Springer
    Planta 158 (1983), S. 288-293 
    Details
    ISSN: 1432-2048
    Keywords: Ammonium, photoproduction ; Chlamydomonas ; Nitrate, nitrite utilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In phototrophically grown Chlamydomonas cells, ammonium strongly inhibited the utilization of nitrate or nitrite. Under darkness, or in the presence of an uncoupler or inhibitor of the non-cyclic photosynthetic electron flow, the utilization of nitrate, nitrite or ammonium was suppressed. l-Methionine-d,l-sulfoximine (MSX) or azaserine, which blocks the assimilation of ammonium, inhibited the consumption of nitrate, but not nitrite, by the cells. Ammonium produced an immediate inhibition of the permease for nitrate in Chlamydomonas growing with nitrate, while ammonium-grown cells lacked this permease. The synthesis of nitrate-reductase activity was dependent on an active permease. In N-starved Chlamydomonas cells, previously treated with MSX, the permease for nitrate was insensitive to inhibition by ammonium, and a significant amount of nitrate reductase was synthetized. These cells photoproduce ammonium by reducing nitrate. Nitrogen-repleted cells, treated with MSX, actively photoproduced ammonium by reducing nitrite, but not nitrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397329
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  • 5
    Electronic Resource
    Electronic Resource
    The NADP-glutamate dehydrogenase of the cyanobacterium Synechocystis 6803: cloning, transcriptional analysis and disruption of the gdhA gene (1995)
    Springer
    Plant molecular biology 28 (1995), S. 173-188 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; gdhA mutant ; glutamate dehydrogenase ; nitrogen metabolism ; growth-phase-specific regulation ; Synechocystis PCC 6803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gdhA gene of Synechocystis PCC 6803, which encodes an NADP-dependent glutamate dehydrogenase (NADP-GDH), has been cloned by complementation of an Escherichia coli glutamate auxotroph. This gene was found to code for a polypeptide of 428 amino acid residues, whose sequence shows high identity with those of archaebacteria (42–47%), some Gram-positive bacteria (40–44%) and mammals (37%). The minimal fragment of Synechocystis DNA required for complementation (2 kb) carries the gdhA gene preceded by an open reading frame (ORF2) encoding a polypeptide of 130 amino acids. ORF2 and gdhA are co-transcribed as a 1.9 kb mRNA, but shorter transcripts including only gdhA were also detected. Two promoter regions were identified upon transcriptional fusion to the cat reporter gene of a promoter probe plasmid. Transcription from the promoter upstream of ORF2 was found to be regulated depending on the growth phase of Synechocystis, in parallel to NADP-GDH activity. This promoter is expressed in Escherichia coli too, in contrast to the second promoter, located between ORF2 and gdhA, which was silent in E. coli and did not respond to the stage of growth in Synechocystis. Disruption of the cyanobacterial gdhA gene with a chloramphenicol resistance cassette yielded a mutant strain totally lacking NADP-GDH activity, demonstrating that this gene is not essential to Synechocystis 6803 under our laboratory conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00042048
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  • 6
    Electronic Resource
    Electronic Resource
    Existence of two ferredoxin-glutamate synthases in the cyanobacterium Synechocystis sp. PCC 6803. Isolation and insertional inactivation of gltB and gltS genes (1995)
    Springer
    Plant molecular biology 27 (1995), S. 753-767 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; ferredoxin ; gltB ; gltS ; glutamate synthase ; Synechocystis sp. PCC 6803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The first two genes of ferredoxin-dependent glutamate synthase (Fd-GOGAT) from a prokaryotic organism, the cyanobacterium Synechocystis sp. PCC 6803, were cloned in Escherichia coli. Partial sequencing of the cloned genomic DNA, of the 6.3 kb Hind III and 9.3 kb Cla I fragments, confirmed the existence of two different genes coding for glutamate synthases, named gltB and gltS. The gltB gene was completely sequenced and encodes for a polypeptide of 1550 amino acid residues (M r 168 964). Comparative analysis of the gltB deduced amino acid sequence against other glutamate synthases shows a higher identity with the alfalfa NADH-GOGAT (55.2%) than with the corresponding Fd-GOGAT from the higher plants maize and spinach (about 43%), the red alga Antithamnnion sp. (42%) or with the NADPH-GOGAT of bacterial source, such as Escherichia coli (41%) and Azospirillum brasilense (45%). The detailed analysis of Synechocystis gltB deduced amino acid sequence shows strongly conserved regions that have been assigned to the 3Fe-4S cluster (CX5CHX3C), the FMN-binding domain and the glutamine-amide transferase domain. Insertional inactivation of gltB and gltS genes revealed that both genes code for ferredoxin-dependent glutamate synthases which were nonessential for Synechocystis growth, as shown by the ferredoxin-dependent glutamate synthase activity and western-blot analysis of the mutant strains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020228
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  • 7
    Electronic Resource
    Electronic Resource
    Electron transport controls transcription of the thioredoxin gene (trxA) in the cyanobacterium Synechocystis sp. PCC 6803 (2000)
    Springer
    Plant molecular biology 43 (2000), S. 23-32 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; electron transport ; light regulation ; Synechocystis sp. PCC 6803 ; thioredoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The trxA gene encoding one of the different thioredoxins of the facultative heterotrophic cyanobacterium Synechocystis sp. PCC 6803 is transcribed as a single mRNA of 450 nucleotides. Transcript accumulation is similar in all standard growth conditions but strongly decreases after transferring cell cultures from light to darkness. In steady-state conditions, trxA transcription is reduced at high (150–500 μE m−2 s−1) compared with moderate (10–50 μE m−2 s−1) light intensities. The stability of the trxA transcript was similar at different light intensities, and also in darkness. Photosynthetic electron transport inhibitors, as well as glucose starvation in a mutant strain lacking photosystem II, promote a strong decline in the level of trxA transcript. Primer extension analysis suggests that trxA is transcribed from two proximal promoters containing a −10 TATA box similar to the Escherichia coli consensus promoters. Unlike the trxA mRNA, the amount of thioredoxin protein was not reduced in the dark, neither at high light intensities, indicating that thioredoxin protein is very stable. Our results indicate that the thioredoxin encoded by the trxA gene is likely to be primarily regulated at the transcriptional level, rather than at the protein level, by the electron transport generated photosynthetically or from glucose metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006472018601
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  • 8
    Electronic Resource
    Electronic Resource
    Electron transport controls transcription of the glutamine synthetase gene (glnA) from the cyanobacterium Synechocystis sp. PCC 6803 (1995)
    Springer
    Plant molecular biology 27 (1995), S. 789-799 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; glnA gene ; glutamine synthetase ; Synechocystis sp. PCC 6803 ; light regulation ; nitrogen assimilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The glnA gene, encoding type I glutamine synthetase (GS) in Synechocystis sp. PCC 6803, showed a high sequence similarity with other cyanobacterial glnA genes. A dramatic decrease in the amount of glnA mRNA, a single transcript of about 1.6 kb, was observed after transfer to darkness, or after incubation with the electron transport inhibitors DCMU or DBMIB. The levels of glnA transcript were fully recovered after 5 min of reillumination. The glnA mRNA was found to be equally stable both in the light and the dark (half-life about 2.5 min). Unlike the glnA messenger, the amount of GS protein was not reduced in the dark. Synthesis of the glnA transcript in the dark required the presence of glucose. In addition, glnA transcription in a Synechocystis psbE-psbF mutant lacking photosystem II required the presence of glucose even when grown in the light. These observations indicate that glnA transcription is under the control of the redox state of the cell. Finally, nitrogen starvation provoked a delay in the decrease of glnA transcript in darkness, suggesting a connection between nitrogen and redox controls of glnA transcript levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020231
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  • 9
    Electronic Resource
    Electronic Resource
    Nitrogen availability and electron transport control the expression of glnB gene (encoding PII protein) in the cyanobacterium Synechocystis sp. PCC 6803 (1997)
    Springer
    Plant molecular biology 35 (1997), S. 723-734 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; glnB gene ; light regulation ; nitrogen regulation ; PII protein ; Synechocystis sp. PCC 6803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The glnB gene from Synechocystis sp. PCC 6803 that encodes the PII protein has been cloned by heterologous hybridization using the corresponding glnB gene from Synechococcus sp. PCC 7942. An ORF of 336 nucleotides appeared that potentially coded for a protein of 112 amino acid residues (Mr 12397). The deduced amino acid sequence revealed a high identity (higher than 80%) with its cyanobacterial counterparts and a basal level of identity (close to 60%) with other PII proteins. A single mRNA of about 680 nucleotides was found under all growth conditions studied. glnB gene expression was specifically activated under nitrogen deprivation (a 10-fold increase respect to nitrogen-replete conditions). No differences in glnB mRNA levels were observed when using nitrate or ammonium as nitrogen sources. Amount of glnB mRNA decreased to undetectable levels when transferring cells to the dark, but effect was avoided by adding glucose to the culture medium. Primer extension analysis and band-shift assays indicated that expression of the glnB gene, elevated under nitrogen deprivation, might lie under the control of the nitrogen transcriptional regulator NtcA, although constitutive levels of expression were also detected from a σ70-dependent Escherichia coli-like promoter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005846626187
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  • 10
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    Unprecedented pathway of reducing equivalents in a diflavin-linked disulfide oxidoreductase (2017)
    National Academy of Sciences
    Details
    Publication Date: 2017-11-13
    Description: Flavoproteins participate in a wide variety of physiologically relevant processes that typically involve redox reactions. Within this protein superfamily, there exists a group that is able to transfer reducing equivalents from FAD to a redox-active disulfide bridge, which further reduces disulfide bridges in target proteins to regulate their structure and function. We have identified a previously undescribed type of flavin enzyme that is exclusive to oxygenic photosynthetic prokaryotes and that is based on the primary sequence that had been assigned as an NADPH-dependent thioredoxin reductase (NTR). However, our experimental data show that the protein does not transfer reducing equivalents from flavins to disulfides as in NTRs but functions in the opposite direction. High-resolution structures of the protein from Gloeobacter violaceus and Synechocystis sp. PCC6803 obtained by X-ray crystallography showed two juxtaposed FAD molecules per monomer in redox communication with an active disulfide bridge in a variant of the fold adopted by NTRs. We have tentatively named the flavoprotein “DDOR” (diflavin-linked disulfide oxidoreductase) and propose that its activity is linked to a thiol-based transfer of reducing equivalents in bacterial membranes. These findings expand the structural and mechanistic repertoire of flavoenzymes with oxidoreductase activity and pave the way to explore new protein engineering approaches aimed at designing redox-active proteins for diverse biotechnological applications.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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