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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Complementary chromatic adaptation is a mechanism by which some cyanobacteria that are able to synthesize phycoerythrin can adapt their pigment (phycobili-protein) content to the incident wavelengths of the light. In Calothrix sp. PCC 7601 it concerns phycoerythrin (cpe operon), synthesized under green light, and phycocyanin-2 (cpc2 operon), expressed under red light, and involves transcriptional controls. With cell-free extracts from Calothrix sp. PCC 7601 grown under various light regimes, a protein designated RcaD was found by gel retardation experiments to specifically bind to the cpc2 promoter region and to be present only in red-light-grown cells. This protein was partially purified and its binding activity was shown to be sensitive to an alkaline phosphatase treatment. RcaO can protect two regions of the cpc2 promoter sequence against degradation by DNase I. Because its activity is detected only under the conditions required for cpc2 expression, we propose that RcaD is a positive effector of transcription.
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  • 2
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Polar mutations were obtained by integration of bacteriophage Mu c + or Mu cts DNA into the Klebsiella pneumoniae nif genes located on plasmid pCE1, a derivative of pRD1. In addition, nif deletions were isolated from nif:: Mu cts plasmids. Complementation data allowed the characterization of twelve nif cistrons, nine corresponding to previously identified genes. Polar effect of Mu DNA insertions suggested the existence of at least six transcription units: 1) nifK, nifD and nifH-2) nifA and nifL-3) nifE and a new gene-4) nifB-5) nifF-6) nifJ. NifK, nifD and nifH, which are most probably the structural genes for nitrogenase, seem to belong to the same operon transcribed from nifH to nifK. This was confirmed by SDS gel autoradiography of pulse labelled proteins. Moreover it was possible to identify, on the autoradiograms, a polypeptide which likely is the product of nifJ and whose biosynthesis is under the control of nifA.
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  • 3
    ISSN: 1617-4623
    Keywords: Complementary chromatic adaptation ; Gene expression ; Photoregulation ; Phycobilisome ; Recombinant DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In cyanobacteria, light is harvested by phycobilisomes which are essentially made up of chromophoric proteins called phycobiliproteins. We have characterized two gene clusters (cpcB1, cpcA1 and cpcB3, cpcA3) each encoding the two subunits of phycocyanin (βPC and αPC, respectively), one of the major phycobiliproteins in Calothrix 7601. Downstream from the gene encoding the PCα subunit in cluster 1, an open reading frame was found, cpcE1. These genes are organized in two transcriptional units, namely: cpcB3 A3 and cpcB1 A1 E1. All these genes are transcribed whatever the chromatic light received during cell growth. Consequently, although only one type of “constitutive” PC has been biochemically characterized, we have demonstrated that there are two cpc operons “constitutively” transcribed in this strain. With the previously described red light “inducible” cpcB2 A2 operon, there are three copies of the PC encoding genes in Calothrix 7601. The significance of this newly described multigene family in cyanobacteria is discussed. We have also mapped the 5′ and 3′ termini of the major transcript from the cpc1 operon. Analysis of the 5′ untranslated region of this transcript has revealed alternative secondary structures which are proposed to play a role in the regulation of the expression of this operon.
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  • 4
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract In the filamentous cyanobacterium Calothrix PCC 7504, which fixes N2 aerobically, the modification state of the regulatory PII protein (GlnB) was shown to depend on nitrogen and carbon availability, as observed in the unicellular non-fixing strain Synechococcus PCC 7942. However, the conditions for modifications, the time dependence of the process and the electrophoretic behavior of the native PII isoforms differed somewhat between the two strains. In another strain, Calothrix PCC 7601, which has lost the capability to fix N2, PII was modified only if ammonia plus an inhibitor of glutamine synthetase were present. It is proposed that: (i) the behavior of the PII proteins depends upon the physiological properties of the strains; and (ii) the modification system of PII per se may differ between the two cyanobacterial genera.
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  • 5
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The plasmid content of 7 unicellular and 4 filamentous cyanobacterial strains has been analyzed. All strains were found to carry small plasmids while some strains harbor large plasmids up to approx. 400 kb. In addition, at least one megaplasmid of about 1000 kb was detected in the unicellular strain Synechococcus PCC7942. In the filamentous strain Calothrix PCC7601, 2 different distribution patterns of plasmids were observed in different subcultures, suggesting the presence of mobile DNA elements in this strain.
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  • 6
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The unicellular facultatively heterotrophic cyanobacterium Synechocystis 6803 harbors 4 plasmids, pSY1–4, of 2.5, 5.2, 50 and 100 kb, respectively. We observed that the loss of the pSY2 plasmid and that of cell motility occurs at a high frequency. However, we showed that there is no direct correlation between these two phenomena, and that cell motility does not require a pSY2-encoded function. In addition, restriction analysis and hybridization experiments showed that pSY1 and pSY2 share no homologous DNA sequences.
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  • 7
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Dating from the Pre-Cambrian era, cyanobacteria have a long history of adaptation to the Earth's environment. By evolving oxygen via photosynthetic reactions similar to those of plants and green algae, these prokaryotes were essential to the evolution of the present biosphere. They continue to make a large contribution to the equilibrium of the Earth's atmosphere by production oxygen and removing carbon dioxide. To survive in extreme or variable environments, cyanobacteria have developed specific regulatory systems, in addition to more general mechanisms equivalent to those of other prokaryotes or photosynthesis eukaryotes. Specific regulatory systems control the differentiation of specialized nitrogen-fixing cells and of cell types facilitating the dispersion of species. In the past decade, considerable progress has been made towards understanding the expression of the cyanobacterial genome in response to variations in the intensity and spectral quality of incident light and in response to nutritional conditions, especially carbon, nitrogen and sulphur sources. These studies have provided insights into the relationships between carbon and nitrogen intermediary metabolism, and a start towards understanding of the interconnected pathways which lead from the perception of environmental signals to the regulation of enzyme activities and gene expression. Cyanobacterial regulatory mechanisms share common features with those of other prokaryotes, but are unique since these essentially photo-autotrophic organisms must maintain a proper cellular C/N balance, in spite of dailty variations in incident light. Thus an appropriate coordination between photosynthesis and other metabolic processes must be achieved through control of the catalytic activity of key enzymes by reducing equivalents and ATP produced by photosynthetic or respiratory electron transport. Recently discovered kinases/phosphatases act by post-translational modification of specific proteins which probably act as signal transducers or modulators of gene expression in a manner similar to the well-known two-component regulatory systems described in other bacteria. In this overview, we present our current knowledge on the molecular aspects of the biology of cyanobacteria, as well as on their mechanisms of resistance to metal ions and their responses to metabolic stress.
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cyanobacteria respond to environmental stress conditions by degrading their phycobilisomes, the light harvesting complexes for photosynthesis. The expression of nblA, a key gene in this process, is controlled by the response regulator NblR in Synechococcus sp. PCC 7942. Here we show that, under nitrogen stress, nblA is also regulated by NtcA, the global regulator for nitrogen control. NtcA activation of nblA was found to be nitrogen-specific and did not take place under sulphur stress. Transcripts from the two major transcription start points (tsp) for the nblA gene were induced in response to nitrogen and sulphur starvation. The most active one (tspII) required both NblR and NtcA to induce full nblA expression under nitrogen starvation. NblR and NtcA bound in vitro to a DNA fragment from the nblA promoter region, suggesting that, under nitrogen stress, both NblR and NtcA activate the main regulated promoter (PnblA-2) by direct DNA-binding. The structure of PnblA-2 differs from that of the canonical NtcA-activated promoter and it is therefore proposed to represent a novel type of NtcA-dependent promoter. We analysed expression patterns from ntcA and selected NtcA targets in NtcA–, NblR– and wild-type strains, and discuss data suggesting further interrelations between phycobilisome degradation and nitrogen assimilation regulatory pathways.
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Although in cyanobacteria many genes have been shown to be transcriptionally controlled by specific stimuli, little is known about promoter structure and the form of RNA polymerase that recognizes individual promoters. RNA polymerase holoenzyme has been purified from Calothrix sp. PCC 7601. its polypeptide composition resembles that of the plant chloroplast enzymes. To study transcription in cyanobacteria further, we have analysed the promoter-recognition properties of the purified enzyme. In vitro transcription was assayed with the promoter of the phycocyanin gene (cpc1) that is expressed whatever the incident light conditions. Transcription initiation at the same start point as in vivo was obtained with the Calothrix sp. PCC 7601 purified enzyme and the Escherichia coli core enzyme supplemented with a Calothrix sp. PCC 7601 sigma factor, but not with the E. coli holoenzyme.
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  • 10
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The two ycf 27 genes from the filamentous cyanobacterium Tolypothrix PCC 7601 have been cloned and sequenced. These two genes, previously designated rpaA and rpaB, encode putative transcriptional regulators of the ‘OmpR’ family. In Synechocystis PCC 6803, homologous genes have been linked to the regulation of transfer of excitation energy from the phycobilisome to photosystem (PS) I and PSII respectively. Partial clones from Spirulina platensis, Dactylococcopsis salina and Synechococcus PCC 7002 have also been sequenced. A table of identity between the proteins confirms that RpaB belongs in the same family as the algal ycf 27 proteins. However, RpaA is a rather different protein and should lose the designation ycf 27. The loss of rpaB from the plastid genomes of eukaryotic algae is associated with the loss of phycobiliproteins, so it is likely that this gene performs a similar role in algae to that in cyanobacteria. The implications for chloroplast evolution are discussed along with the possible identity of the cognate histidine kinase gene in the plastid genomes.
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