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

Nitrite, either exogenously supplied or endogenously generated by nitrate reduction, activates transcription of the nitrate assimilation operon (nirA-nrtABCD-narB) in Synechococcus sp. strain PCC 7942 cells treated with L-methionine-DL-sulfoximine (an inhibitor of glutamine synthetase), in which there is no negative feedback resulting from fixation of the ammonium generated by nitrite reduction (Kikuchi et al., J. Bacteriol. 178:5822-5825, 1996). Other transcription units related to nitrogen assimilation, i.e., the nirB-ntcB operon, glnA, and ntcA, were not activated by nitrite. Nitrite did not activate nirA operon transcription in a mutant with a deletion of ntcB, an ammonium-repressible gene encoding a LysR-type DNA-binding protein. Introduction of plasmid-borne ntcB into the ntcB deletion mutant restored the response of the cells to nitrite, indicating that NtcB activates the nirA operon in response to nitrite. Supplementation of nitrite or nitrate to nitrogen-starved cultures of the wild-type strain, but not of the ntcB deletion mutant, caused activation of the nirA operon without L-methionine-DL-sulfoximine treatment of the cells. The results suggested that the positive-regulation mechanism of nirA operon transcription plays a role in rapid adaptation of nitrogen-starved cells to changing availability of nitrate and nitrite.
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PMID:Involvement of NtcB, a LysR family transcription factor, in nitrite activation of the nitrate assimilation operon in the cyanobacterium Synechococcus sp. strain PCC 7942. 924 51

An open reading frame (slr0899) on the genome of Synechocystis sp. strain PCC 6803 encodes a polypeptide of 149 amino acid residues, the sequence of which is 40% identical to that of cyanase from Escherichia coli. Introduction into a cyanase-deficient E. coli strain of a plasmid-borne slr0899 resulted in expression of low but significant activity of cyanase. Targeted interruption of a homolog of slr0899 from Synechococcus sp. strain PCC 7942, encoding a protein 77% identical to that encoded by slr0899, resulted in loss of cellular cyanase activity. These results indicated that slr0899 and its homolog in the strain PCC 7942 represent the cyanobacterial cyanase gene (designated cynS). While cynS of strain PCC 6803 is tightly clustered with the four putative molybdenum cofactor biosynthesis genes located downstream, cynS of strain PCC 7942 was found to be tightly clustered with the two genes located upstream, which encode proteins similar to the subunits of the cyanobacterial nitrate-nitrite transporter. In both strains, cynS was transcribed as a part of a large transcription unit and the transcription was negatively regulated by ammonium. Cyanase activity was low in ammonium-grown cells and was induced 7- to 13-fold by inhibition of ammonium fixation or by transfer of the cells to ammonium-free media. These findings indicated that cyanase is an ammonium-repressible enzyme in cyanobacteria, the expression of which is regulated at the level of transcription. Similar to other ammonium-repressible genes in cyanobacteria, expression of cynS required NtcA, a global nitrogen regulator of cyanobacteria.
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PMID:Identification and nitrogen regulation of the cyanase gene from the cyanobacteria Synechocystis sp. strain PCC 6803 and Synechococcus sp. strain PCC 7942. 929 30

In Synechococcus sp. strain PCC 7942, an ATP-binding cassette transporter encoded by the genes nrtA, nrtB, nrtC, and nrtD mediates active transport of nitrate and nitrite, which is inhibited by ammonium, a preferred source of nitrogen for the cyanobacterium. One of the ATP-binding subunits of the transporter, NrtC, has a distinct C-terminal domain of 380 amino acid residues. A mutant NC2, constructed by removal of this domain using genetic engineering techniques, assimilated low concentrations of nitrate and nitrite and accumulated nitrate intracellularly, showing that the domain is not essential for the transporter activities. Assimilation of low concentrations of nitrite was only partially inhibited by ammonium in NC2 but was completely inhibited in the wild-type cells. Cells of NC2 and its derivative (nitrate reductase-less strain NC4) carrying the truncated NrtC but not the cells with the wild-type NrtC accumulated nitrate intracellularly in the presence of ammonium in medium. These findings indicated that the C-terminal domain of NrtC is involved in the ammonium-promoted inhibition of the nitrate/nitrite transporter. In the presence of ammonium, NC2 could not assimilate nitrate despite its ability to accumulate nitrate intracellularly, which suggested that reduction of intracellular nitrate by nitrate reductase is also subject to inhibition by ammonium.
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PMID:Involvement of the C-terminal domain of an ATP-binding subunit in the regulation of the ABC-type nitrate/nitrite transporter of the Cyanobacterium synechococcus sp. strain PCC 7942. 934 Nov 63

NtcA has been identified as a nitrogen-responsive regulatory protein required for nitrogen assimilation and heterocyst differentiation in cyanobacteria. It is proposed that NtcA functions through the formation of DNA-protein complexes with its specific target sequence within the promoter regions of the regulated genes. In vitro, NtcA of Anabaena PCC 7120 binds to upstream regions of the genes whose products are involved in nitrogen assimilation, but also to the upstream region of rbcLS (carbon-fixation gene), xisA (encoding a site-specific recombinase expressed during heterocyst differentiation) and ntcA (encoding NtcA itself). However, the mechanism by which NtcA serves as a critical regulator for such diverse processes is not understood. With the use of electrophoretic mobility shift assays, NtcA from Anabaena PCC 7120 was here shown to interact with the promoter sequence of the gor gene, encoding glutathione reductase, thereby providing a novel example of NtcA's acting as a repressor, previously found only for the rbcLS gene. Furthermore we demonstrate that the binding of DNA by NtcA is regulated in vitro by a redox-dependent mechanism involving cysteine residues of the NtcA protein. These findings suggest that NtcA is a transcriptional regulator that responds not only to the nitrogen status but also to the cellular redox status, a function that might be particularly significant during heterocyst differentiation.
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PMID:Evidence for redox regulation of the transcription factor NtcA, acting both as an activator and a repressor, in the cyanobacterium Anabaena PCC 7120. 935 24

The expression of a 126 kDa protein in the cytoplasmic membrane of Synechococcus PCC 7942 is shown to be dependent on the nitrogen source. It is absent in ammonium-grown cells and its quantity is inversely related to the concentration of nitrate or nitrite in the growth medium. Addition of ammonium-grown cells to a medium containing nitrate or L-methionine-DL-sulfoximine results in the expression of this protein. It is present in the plasmalemma of the Synechococcus NC3 mutant (nrtC gene deleted) and absent in the NA3 mutant (nrtABCD genes deleted). These results may suggest involvement of the 126 kDa protein in nitrate transport through Synechococcus cytoplasmic membrane.
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PMID:Nitrogen source-dependent expression of a 126 kDa protein in the plasma membrane of the cyanobacterium Synechococcus PCC 7942. 936 9

Transposon-generated mutant C3 of Anabaena sp. strain PCC 7120 is unable to form heterocysts upon deprivation of combined nitrogen but forms a pattern of spaced, weakly fluorescent cells after 2 days of deprivation. Sequence analysis of chromosomal DNA adjacent to the ends of transposon Tn5-1058 in mutant C3 showed a 1,044-amino-acid open reading frame, designated hetC, whose predicted protein product throughout its C-terminal two-thirds has extensive similarity to the HlyB family of bacterial protein exporters. Its N-terminal third is unique and does not resemble any known protein. hetC lies 1,165 bp 5' from the previously described gene hetP. Reconstruction of the C3 mutation and its complementation in trans with a wild-type copy of hetC confirmed that hetC has an essential regulatory role early in heterocyst development. hetC is induced ca. 4 h after nitrogen stepdown, hours after induction of hetR. Expression of hetC depends on HetR and may depend on HetC. Highly similar sequences are present 5' from the initiation codons and in the 3' untranslated regions of hetC and of two heterocyst-specific genes, devA and hetP.
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PMID:hetC, a gene coding for a protein similar to bacterial ABC protein exporters, is involved in early regulation of heterocyst differentiation in Anabaena sp. strain PCC 7120. 937 42

The phosphorylation state of the putative signal transduction protein P(II) from the cyanobacterium Synechococcus sp. strain PCC 7942 depends on the cellular state of nitrogen and carbon assimilation. In this study, dephosphorylation of phosphorylated P(II) protein (P[II]-P) was investigated both in vivo and in vitro. The in vivo studies implied that P(II)-P dephosphorylation is regulated by inhibitory metabolites involved in the glutamine synthetase-glutamate synthase pathway of ammonium assimilation. An in vitro assay for P(II)-P dephosphorylation was established that revealed a Mg2+-dependent P(II)-P phosphatase activity. P(II)-P phosphatase and P(II) kinase activities could be separated biochemically. A partially purified P(II)-P phosphatase preparation also catalysed the dephosphorylation of phosphoserine/phosphothreonine residues on other proteins in a Mg2+-dependent manner. However, only dephosphorylation of P(II)-P was regulated by synergistic inhibition by ATP and 2-oxoglutarate. As the same metabolites stimulate the P(II) kinase activity, it appears that the phosphorylation state of P(II) is determined by ATP and 2-oxoglutarate-dependent reciprocal reactivity of P(II) towards its phosphatase and kinase.
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PMID:Dephosphorylation of the phosphoprotein P(II) in Synechococcus PCC 7942: identification of an ATP and 2-oxoglutarate-regulated phosphatase activity. 938 91

The coloration of cells of the cyanobacterium Synechococcus sp. PCC 7002 changed from normal blue-green to yellow-green when cells were grown at 15 degrees C in a medium containing nitrate as the sole nitrogen source. This change of coloration was similar to a general response to nutrient deprivation (chlorosis). For the chlorotic cells at 15 degrees C, the total amounts of phycobiliproteins and chlorophyll a decreased, high levels of glycogen accumulated, and growth was arithmetic rather than exponential. These changes in composition and growth occurred in cells grown at low (50 microE m-2 s-1) as well as high (250 microE m-2 s-1) light intensity. After a temperature shift-up to 38 degrees C, chlorotic cells rapidly regained their normal blue-green coloration and normal exponential growth rate within 7 h. When cells were grown at 15 degrees C in a medium containing urea as the reduced nitrogen source, cells grew exponentially and the symptoms of chlorosis were not observed. The decrease in photosynthetic oxygen evolution activity at low temperature was much smaller than the decrease in growth rate for cells grown on nitrate as the nitrogen source. These studies demonstrate that low-temperature-induced chlorosis of Synechococcus sp. PCC 7002 is caused by nitrogen limitation and is not the result of limited photosynthetic activity or photodamage to the photosynthetic apparatus, and that nitrogen assimilation is an important aspect of the low-temperature physiology of cyanobacteria.
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PMID:Growth at low temperature causes nitrogen limitation in the cyanobacterium Synechococcus sp. PCC 7002. 939 30

Cyanobacteria acclimate to low temperature by desaturating their membrane lipids. Mutant strains of Synechococcus sp. PCC 7002 containing insertionally inactivated desA (Delta12 acyl-lipid desaturase) and desB (omega3 acyl-lipid desaturase) genes were produced, and their low-temperature susceptibility was characterized. The desA mutant synthesized no linoleic acid or alpha-linolenic acid, and the desB mutant did not produce alpha-linolenic acid. The desA mutant grew more slowly than the wild-type at 22 degrees C and could not grow at 15 degrees C. The desB mutant could not continuously grow at 15 degrees C, although no observable phenotype appeared at higher temperatures. It has been shown that expression of the desA gene occurs at 38 degrees C and is up-regulated at 22 degrees C, and that the desB gene is only expressed at 22 degrees C. These results indicate that the expression of the desA and desB genes occurs at higher temperatures than those at which a significant decline in physiological activities is caused by the absence of their products. The temperature dependency of photosynthesis was not affected by these mutations. Since chlorosis and inability to grow at 15 degrees C with nitrate was suppressed by the substitution of urea as a nitrogen source, it is very likely that the chilling susceptibility of the desaturase mutants is attributable to nutrient limitation.
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PMID:Alteration of low-temperature susceptibility of the cyanobacterium Synechococcus sp. PCC 7002 by genetic manipulation of membrane lipid unsaturation. 939 31

Tyrosine D (TyrD), a side path electron carrier of photosystem II (PS II), has been studied by light-induced Fourier transform infrared (FTIR) difference spectroscopy in PS II core complexes of Synechocystis sp. PCC 6803 using the experimental conditions previously optimized to generate the pure TyrD./TyrD FTIR difference spectrum in PS II-enriched membranes of spinach [Hienerwadel, R., Boussac, A., Breton, J., and Berthomieu, C. (1996) Biochemistry 35, 115447-115460]. IR modes of TyrD and TyrD. have been identified by specific 2H- or 13C-labeling of the tyrosine side chains. The v8a(CC) and v19(CC) IR modes of TyrD are identified at 1615 and 1513-1510 cm-1, respectively. These frequencies show that TyrD is protonated. Comparison of isotope-sensitive signals in situ with those of the model compound p-methylphenol dissolved in different solvents leads to the assignment of the v7'a(CO) and delta(COH) modes of TyrD at 1275 and 1250 cm-1, respectively. It is shown that these modes and in particular the delta(COH) IR mode are very sensitive to the formation of hydrogen-bonded complexes with amide C=O or with imidazole nitrogen atoms. The frequencies observed in situ show that TyrD is hydrogen-bonded to the imidazole ring of a neutral histidine. For the radical TyrD., isotope-sensitive IR modes are identified at 1532 and 1503 cm-1. The signal at 1503 cm-1 is assigned to the v(CO) mode of TyrD. since it is sensitive to 13C-labeling at the ring carbon involved in the C4-O bond. The perturbation of TyrD and TyrD. IR modes upon site-directed replacement of D2-His189 by Gln confirms that a hydrogen bond exists between both TyrD and TyrD. and D2-His189. In the D2-His189Gln mutant, the v7'a(CO) mode of TyrD at 1267 cm-1 and the delta(COH) mode at approximately 1228 cm-1 show that a hydrogen bond is formed between TyrD and an amide carbonyl, probably that of the D2-Gln189 side chain. Electron nuclear double resonance (ENDOR) measurements have shown that TyrD. is hydrogen-bonded in the wild type but not in the mutant [Tang, X.-S., Chrisholm, D. A., Dismukes, G. C., Brudwig, G. W., and Diner, B. A. (1993) Biochemistry 32, 13742-13748]. The v(CO) mode of TyrD. at 1497 cm-1 is downshifted by 6 cm-1 compared to WT PS II, indicating that hydrogen bonding induces a frequency upshift of the v(CO) IR mode of Tyr.. IR signals from the Gln side chain v(C=O) mode are proposed to contribute at 1659 and 1692 cm-1 in the TyrD and TyrD. states, respectively. These frequencies are consistent with the rupture of a hydrogen bond upon TyrD. formation in the mutant. The frequency of the v(CO) mode of TyrD., observed at 1503 cm-1 for WT PS II, is intermediate between that observed at 1497 cm-1 in the D2-His189Gln mutant and at 1513 cm-1 for Tyr. formed by UV irradiation in borate buffer, suggesting weaker or fewer hydrogen bonds for TyrD. in PS II than in solution. The role of D2-His189 in proton uptake upon TyrD. formation is also investigated.
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PMID:Fourier transform infrared difference spectroscopy of photosystem II tyrosine D using site-directed mutagenesis and specific isotope labeling. 939 91


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