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Query: UMLS:C1832526 (PCC)
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The Anabaena sp. strain PCC 7120 ntcA gene showed multiple transcripts with different 5' ends. The relative abundance of transcripts varied in response to nitrogen availability. The ntcA product, NtcA, showed binding to the promoter region of its own gene. The binding site mapped to a region between the transcription start site used under nitrogen-replete conditions and the start sites used under nitrogen-limiting conditions, suggesting that NtcA regulates its own expression.
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PMID:Transcription of the Anabaena sp. strain PCC 7120 ntcA gene: multiple transcripts and NtcA binding. 855 May 35

A mutant (M45) of the cyanobacterium Synechococcus sp. strain PCC 7942, which is defective in active transport of nitrate, was used for the studies of the nitrogen regulation of the genes involved in nitrate and CO2 assimilation. In a medium containing 30 mM nitrate as the nitrogen source, M45 grew under constant stress of nitrogen deficiency and accumulated a five-times-larger amount of the transcript of nirA, the gene for nitrite reductase, compared with nitrate-grown wild-type cells. By contrast, the level of the transcript of rbcL, the gene for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was 40% of the wild-type level. Addition of ammonium to the culture of M45 abolished the accumulation of the nirA transcript and stimulated the accumulation of the rbcL transcript, showing that ammonium repressed and activated the transcription of nirA and rbcL, respectively. Glutamine, the initial product of ammonium fixation, also showed negative and positive effects on nirA and rbcL, respectively. One of the metabolites of glutamine, carbamoylphosphate, and its decomposition product, cyanate, were found to repress nirA and also to markedly activate rbcL. Cyanate negatively regulated another ammonium-repressible gene, glnA, but had no effect on the psbAI and rps1 genes. The effects of cyanate were not ascribable to the ammonium and CO, resulting from its decomposition. These findings suggested that cyanate may act as a regulator of the ammonium-responsive genes involved in carbon and nitrogen assimilation in the cyanobacterium.
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PMID:Regulation by cyanate of the genes involved in carbon and nitrogen assimilation in the cyanobacterium Synechococcus sp. strain PCC 7942. 862 39

The expression of ferredoxin-NADP+ reductase (FNR) from Anabaena sp. PCC 7119 in heterocysts and vegetative cells has been quantified. Specific reductase activity in heterocysts was approximately 10 times higher than in vegetative cells, corresponding to the increased FNR protein content. This was confirmed by immunoquantification of the FNR protein from whole filaments of Anabaena sp. PCC 7120 grown in media with and without combined nitrogen. Transcription of the petH gene was markedly enhanced in the absence of combined nitrogen. This suggests that the increased RNA level is mainly responsible for the up-regulation of FNR in heterocysts. As has been observed for nif genes, iron deficiency also increased transcription of petH. Characterization of the FNR purified from isolated heterocysts showed no detectable differences from the enzyme from vegetative cells. Although nitrogen stress was a key regulatory factor, localization of the petH gene in the genomic map of Anabaena PCC 7120 showed that this gene is not physically associated with the nif cluster.
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PMID:Expression of ferredoxin-NADP+ reductase in heterocysts from Anabaena sp. 864 99

Mutants of Anabaena sp. strain PCC 7120 that form heterocysts when grown on nitrate-containing media were isolated following nitrosoguanidine mutagenesis. Six independent mutants were isolated, and the characterization of one mutant, strain AMC260, which forms 6 to 8% heterocysts in the presence of nitrate, is presented. A 1.8-kb chromosomal fragment that complemented the AMC260 mutant was sequenced, and a 1.2-kb open reading frame, named moeA, was identified. The deduced amino acid sequence of the predicted Anabaena sp. strain PCC 7120 MoeA polypeptide shows 37% identity to MoeA from Escherichia coli, which is required for the synthesis of molybdopterin cofactor. Molybdopterin is required by various molybdoenzymes, such as nitrate reductase. Interruption of the moeA gene in Anabaena sp. strain PCC 7120 resulted in a strain, AMC364, that showed a phenotype similar to that of AMC260. We show that AMC260 and AMC364 lack methyl viologen-supported nitrate reductase activity. We conclude that the inability of the moeA mutants to metabolize nitrate results in heterocyst formation on nitrate-containing media. Northern (RNA) analysis detected a 1.5-kb moeA transcript in wild-type cells grown in the presence or absence of a combined nitrogen source.
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PMID:Nitrate reductase activity and heterocyst suppression on nitrate in Anabaena sp. strain PCC 7120 require moeA. 868 95

Two different fdxH genes (fdxH1, fdxH2) have been isolated from the nitrogen-fixing, heterocyst-forming cyanobacterium Anabaena variabilis ATCC 29413. They are part of two different nif gene clusters, nif1 and nif2. fdxH1 encodes the [2Fe-2S] ferredoxin that is known as the direct electron donor to nitrogenase in heterocysts, and is very similar to FdxH from Anabaena sp. PCC 7120. FdxH2 has more residues in common and shares its oxygen sensitivity with the single FdxH from the non-heterocystous, filamentous cyanobacterium Plectonema boryanum PCC 73110. The latter expresses nitrogenase early (< or = 3-4h) after nitrogen depletion in vegetative cells and exclusively under anaerobic conditions. fdxH2 and the nif2 genes of Anabaena 29413 are also transcribed < or = 4 h after onset of nitrogen-stepdown, exclusively under anaerobic growth conditions and long before functional heterocysts appear. At this time, no fdxH1 and nif1 gene transcription was observed. It occurred later and was associated with nitrogen fixation under aerobic conditions, i.e. within heterocysts. fdxH2 and nifHDK2 were not transcribed during aerobic, nitrogen-fixing growth. In addition, neither was an fdxH2-type gene found nor an anaerobically and early inducible Nif2 system detectable in Anabaena 7120. These data reveal that in filamentous cyanobacteria two different Nif systems have evolved based on molybdenum nitrogenases. It is concluded that a Nif2-type system operates in vegetative cells of non-heterocystous and some, but not all, heterocyst-forming filamentous cyanobacteria. It is environmentally regulated by the levels of both oxygen and combined nitrogen in the habitat. To simultaneously allow for oxygen-evolving photosynthesis and oxygen-sensitive nitrogen fixation, the Nif1-type system probably branched from an ancestral Nif2-type system and has evolved for an exclusive operation within heterocysts. Accordingly, its expression has become an obligate late event in the developmental programme of heterocyst differentiation, irrespective of aerobic or anaerobic growth conditions.
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PMID:Distinct and differently regulated Mo-dependent nitrogen-fixing systems evolved for heterocysts and vegetative cells of Anabaena variabilis ATCC 29413: characterization of the fdxH1/2 gene regions as part of the nif1/2 gene clusters. 870 54

NADP+-isocitrate dehydrogenase (NADP+-IDH) activity and protein levels in crude extracts from the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 and the filamentous, dinitrogen-fixing Anabaena sp. strain PCC 7120 were determined under different nitrogen conditions. The highest NADP+-IDH activity and protein accumulation were found under dinitrogen-fixing conditions for the Anabaena strain and under nitrogen starvation for Synechocystis sp. PCC 6803. The icd gene that encodes the NADP+-IDH from Synechocystis sp. strain PCC 6803 was cloned by heterologous hybridization with the previously isolated icd gene from Anabaena sp. strain PCC 7120. The two cyanobacterial icd genes show 81% sequence identity and share a typical 44-amino-acid region different from all the other icd genes sequenced so far. The icd gene seems to be essential for Synechocystis growth since attempts to generate a completely segregated icd mutant were unsuccessful. Transcripts of 2.0 and 1.6 kb were detected by Northern (RNA) blot analysis, for the Anabaena and Synecho-cystis icd genes, respectively. Maximal icd mRNA accumulation was reached after 5 It of nitrogen starvation in Synechocystis cells and under dinitrogen-fixing conditions in Anabaena cells. Primer extension analysis showed that the structure of the Synechocystis icd gene promoter resembles those of the NtcA-regulated promoters. In addition, mobility shift assays demonstrated that purified Synechocystis NtcA protein binds to the promoter of the icd gene. All these data suggest that the expression of the icd gene from Synechocystis sp. strain PCC 6803 may be subjected to nitrogen control mediated by the positively acting regulatory protein NtcA.
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PMID:The NADP+-isocitrate dehydrogenase gene (icd) is nitrogen regulated in cyanobacteria. 876 33

In the absence of fixation of ammonium to glutamine, nitrate and nitrite activated transcription of the nitrate assimilation (nirA-nrtABCD-narB) operon of Synechococcus sp. strain PCC 7942. In a nitrate reductase-deficient mutant, only nitrite activated transcription, indicating that nitrite is the actual activator of the operon. Nitrate and nitrite were also found to activate the transcription of a nitrate assimilation operon in the filamentous nonheterocystous nitrogen-fixing cyanobacterium Plectonema boryanum.
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PMID:Positive regulation by nitrite of the nitrate assimilation operon in the cyanobacteria Synechococcus sp. strain PCC 7942 and Plectonema boryanum. 882 36

Cyanobacteria can utilize nitrate or ammonium as a source of fixed nitrogen for cell growth. In the filamentous Calothrix sp. strain PCC 7601, these two sources of nitrogen differently influenced the phycobiliprotein composition of the phycobilisomes, the major light-harvesting antennae. When compared to nitrate, growth in the presence of ammonium resulted in intracellular steady-state levels 35% lower for phycoerythrin and 46% higher for phycocyanin. Besides these differences in cell pigmentation, a rapid but transient accumulation of cyanophycin granule polypeptide occurred in ammonium-grown cells, while these macromolecules were not detected in cells grown with nitrate. In contrast, glycogen reserves displayed a dynamic pattern of accumulation and disappearance during cell growth which varied only slightly with the nitrogen source. The observed changes in cell pigmentation are reminiscent of the phenomenon of complementary chromatic adaptation, in which green and red wavelengths promote the syntheses of phycoerythrin and phycocyanin-2, respectively. As in complementary chromatic adaptation, the regulation of synthesis of phycoerythrin and phycocyanin-2 by the nitrogen source occurred mainly at the mRNA level. Moreover, the transcriptional start sites for the expression of the cpeBA and the cpc2 operons, which respectively encode the two subunits of phycoerythrin and phycocyanin-2, were the same in cells grown in nitrate or ammonium, and identical to those in green- and red-light-grown cells. The results of this study suggest that acclimation to the spectral light quality and to the nitrogen source share some common regulatory elements.
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PMID:Effect of the nitrogen source on phycobiliprotein synthesis and cell reserves in a chromatically adapting filamentous cyanobacterium. 886 36

Glucose-6-phosphate dehydrogenase is a particularly important enzyme in carbon catabolism in the chloroplasts of higher plants and in cyanobacteria. It catalyzes the first reaction in the oxidative pentose phosphate pathway which supplies reduced NADP for a variety of biosynthetic processes. The enzyme is known to be regulated by light. However, the dehydrogenase from plants has been difficult to purify and there is little information on kinetics and mechanism of deactivation. The glucose-6-phosphate dehydrogenase from the heterocystous cyanobacterium, Anabaena sp. PCC 7120, was purified to near homogeneity by chromatography on 2',5'-ADP Sepharose chromatography. The cyanobacterial enzyme apparently has different aggregation states or conformations depending on its concentration in solution and the pH. At a pH of 8.0 and low ionic strength, the enzyme has relatively low activity and exhibits sigmoidal kinetics on binding substrate and cofactor. Activity increases and the enzyme exhibits the more classical hyperbolic kinetics at pH 7.0. At the lower pH, glucose-6-phosphate dehydrogenase is inhibited by catalytic amounts of reduced thioredoxin-1 from Anabaena sp. The second thioredoxin from the cyanobacterium is much less effective, although its inhibitory effect is still greater than that of small molecule reducing agents such as glutathione. Glutamine was reported to stabilize the isolated enzyme, but actually is an activator at pH 8.0. The results suggest that cellular demand for reduced cofactor under nitrogen-fixing conditions overrides the pH-induced deactivation.
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PMID:Glucose-6-phosphate dehydrogenase from the cyanobacterium, Anabaena sp. PCC 7120: purification and kinetics of redox modulation. 890 Apr 2

The glbN gene of Nostoc commune UTEX 584 is juxtaposed to nifU and nifH, and it encodes a 12-kDa monomeric hemoglobin that binds oxygen with high affinity. In N. commune UTEX 584, maximum accumulation of GlbN occurred in both the heterocysts and vegetative cells of nitrogen-fixing cultures when the rate of oxygen evolution was repressed to less than 25 micromol of O2 mg of chlorophyll a(-1) h(-1). Accumulation of GlbN coincided with maximum synthesis of NifH and ferredoxin NADP+ oxidoreductase (PetH or FNR). A total of 41 strains of cyanobacteria, including 40 nitrogen fixers and representing 16 genera within all five sections of the cyanobacteria were screened for the presence of glbN or GlbN. glbN was present in five Nostoc strains in a single copy. Genomic DNAs from 11 other Nostoc and Anabaena strains, including Anabaena sp. strain PCC 7120, provided no hybridization signals with a glbN probe. A constitutively expressed, 18-kDa protein which cross-reacted strongly with GlbN antibodies was detected in four Anabaena and Nostoc strains and in Trichodesmium thiebautii. The nifU-nifH intergenic region of Nostoc sp. strain MUN 8820 was sequenced (1,229 bp) and was approximately 95% identical to the equivalent region in N. commune UTEX 584. Each strand of the DNA from the nifU-nifH intergenic regions of both strains has the potential to fold into secondary structures in which more than 50% of the bases are internally paired. Mobility shift assays confirmed that NtcA (BifA) bound a site in the nifU-glbN intergenic region of N. commune UTEX 584 approximately 100 bases upstream from the translation initiation site of glbN. This site showed extensive sequence similarity with the promoter region of glnA from Synechococcus sp. strain PCC 7942. In vivo, GlbN had a specific and prominent subcellular location around the periphery of the cytosolic face of the cell membrane, and the protein was found solely in the soluble fraction of cell extracts. Our hypothesis is that GlbN scavenges oxygen for and is a component of a membrane-associated microaerobically induced terminal cytochrome oxidase.
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PMID:GlbN (cyanoglobin) is a peripheral membrane protein that is restricted to certain Nostoc spp. 893 16


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