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Query: UMLS:C1832526 (PCC)
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Photosystem I is one of the two multisubunit pigment-protein complexes in the thylakoid membranes of cyanobacteria. Subunit III of photosystem I complex was isolated from a mutant of the cyanonbacterium Synechocystis sp PCC 6803, which lacks subunit II. The sequence of its NH2-terminal residues was determined and corresponding oligonucleotide probes were used to isolate the gene encoding this subunit. The gene, designated as psaF, codes for a mature protein of 15705 Da that is synthesized with a 23-amino acid extension. The deduced amino acid sequence is homologous to subunit III from spinach and Chlamydomonas reinhardtii. The presequence of subunit III shows characteristics typical of bacterial presequences and exhibits remarkable amino acid identity around the proteolytic processing site when compared to corresponding regions from the precursors of eukaryotic subunit III. There are two conserved hydrophobic regions in the mature subunit III which may cross or interact with thylakoid membrane. The gene psaF exists as a single copy in the genome and is expressed as a monocistronic RNA. A stable mutant strain in which the gene psaF was replaced by a gene conferring resistance to kanamycin was generated by targeted mutagenesis. Photoautotrophic growth of the mutant strain was comparable with that of the wild type suggesting that function of subunit III is dispensable for photosynthesis in Synechocystis sp. PCC 6803. Addition of more MgSO4 to BG11 medium enhanced growth of the mutant strain but not of the wild type cells.
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PMID:Molecular cloning and targeted mutagenesis of the gene psaF encoding subunit III of photosystem I from the cyanobacterium Synechocystis sp. PCC 6803. 193 76

Glutamate was converted to the chlorophyll and heme precursor delta-aminolevulinic acid in soluble extracts of Euglena gracilis. delta-Aminolevulinic acid-forming activity depended on the presence of native enzyme, glutamate, ATP, Mg2+, NADPH or NADH, and RNA. The requirement for reduced pyridine nucleotide was observed only if, prior to incubation, the enzyme extract was filtered through activated carbon to remove firmly bound reductant. Dithiothreitol was also required for activity after carbon treatment. delta-Aminolevulinic acid formation was stimulated by RNA from various plant tissues and algal cells, including greening barley leaves and members of the algal groups Chlorophyta (Chlorella vulgaris, Chlamydomonas reinhardtii), Rhodophyta (Cyanidium caldarium), Cyanophyta (Anacystis nidulans, Synechocystis sp. PCC 6803), and Prochlorophyta (Prochlorothrix hollandica), but not by RNA derived from Escherichia coli, yeast, wheat germ, bovine liver, and Methanobacterium thermoautotrophicum. E. coli glutamate-specific tRNA was inhibitory. Several of the RNAs that did not stimulate delta-aminolevulinic acid formation nevertheless became acylated when incubated with glutamate in the presence of Euglena enzyme extract. RNA extracted from nongreen dark-grown wild-type Euglena cells was about half as stimulatory as that from chlorophyllous light-grown cells, and RNA from aplastidic mutant cells stimulated only slightly. delta-Aminolevulinic acid-forming enzyme activity was present in extracts of light-grown wild-type cells, but undetectable in extracts of aplastidic mutant and dark-grown wild-type cells. Gabaculine inhibited delta-aminolevulinic acid formation at submicromolar concentration. Heme inhibited 50% at 25 microM, but protoporphyrin IX, Mg-protoporphyrin IX, and protochlorophyllide inhibited only slightly at this concentration.
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PMID:Enzymatic conversion of glutamate to delta-aminolevulinic acid in soluble extracts of Euglena gracilis. 244 64

The kinetics of reduction of soluble ferredoxin by photosystem I (PSI), both purified from the cyanobacterium Synechocystis sp. PCC 6803, were investigated by flash-absorption spectroscopy between 460 and 600 nm. Most experiments were made with isolated monomeric PSI reaction centers prepared with the detergent beta-dodecyl maltoside. Analysis of absorption transients, in parallel at 480 and 580 nm and under several conditions, shows the existence of three different first-order components in the presence of ferredoxin (t1/2 approximately 500 ns, 20 microseconds, and 100 microseconds). A second-order phase of ferredoxin reduction is also present [k = (2-5) x 10(8) s-1 at pH 8 and at moderate ionic strength]. Similar first-order kinetic components were found with membranes from Synechocystis, with dissolved crystals of trimeric PSI reaction centers from Synechococcus, and also when ferredoxin from Synechocystis is replaced by ferredoxin from Chlamydomonas reinhardtii. The three first-order phases exhibit similar, though not identical, spectra which are consistent with electron transfer from the [4Fe-4S] centers of PSI to the [2Fe-2S] center of ferredoxin and are all attributed to reduction of ferredoxin bound to PSI. At pH 8 and at moderate ionic strength, the dissociation constants associated with each of these components are also similar, with a global value varying between 0.2 and 0.8 microM in different cyanobacterial preparations. The presence of three exponential components is discussed assuming homogeneity of the two partners and using the estimated values for the shortest possible distance of approach of soluble ferredoxin from the different iron-sulfur centers of PSI. It is concluded that the 500-ns phase corresponds to electron transfer from either FA- or FB-, the terminal iron-sulfur acceptors of PSI, to ferredoxin and that the immediate electron donor to ferredoxin is reduced within less than 500 ns. The presence of at least two different types of PSI-ferredoxin complex, all competent in electron transfer, is also deduced from the kinetic behavior.
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PMID:Laser flash absorption spectroscopy study of ferredoxin reduction by photosystem I in Synechocystis sp. PCC 6803: evidence for submicrosecond and microsecond kinetics. 803 83

The dark stable neutral tyrosine radical YD. of photosystem 2 (PS2) has been studied using electron nuclear double-resonance (ENDOR) and electron paramagnetic resonance (EPR) spectroscopies. The proton hyperfine coupling constants of all four ring protons and both beta-methylene protons have been determined for YD. in three species covering the range of oxygenic organisms; a higher plant (spinach), an alga (Chlamydomonas reinhardtii), and a cyanobacterium (Phormidium laminosum). It has generally been assumed that the properties of Yd. are the same in all oxygenic organisms, while in fact there are small but significant differences. The beta-proton coupling constants are shown to be species dependent while the ring proton coupling constants are not. Estimation of the electron spin density distribution of Yd. from all three organisms has been done. This shows that changes in beta-proton coupling constants in each organism arise from the slightly different orientation of the tyrosine ring, relative to the beta-protons. The electron spin density distribution within the tyrosine ring is organism independent. The variations in the beta-proton coupling constants are reflected in the corresponding EPR spectra, where small variations in line width have been detected. These data delineate the range of natural variation in the spectroscopic properties of YD., and by assigning the features of the ENDOR spectrum, provide a basis for both the unification of studies of YD. in different organisms and the study of YZ.. The results are discussed in relation to data in the recent study (Hoganson & Babcock, 1992) using YD. in the cyanobacterium, Synechocystis PCC 6803.
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PMID:The dark stable tyrosine radical of photosystem 2 studied in three species using ENDOR and EPR spectroscopies. 811 Jul 76

Plastid genes are transcribed by DNA-dependent RNA polymerase(s), which have been incompletely characterized and have been examined in a limited number of species. Plastid genomes contain rpoA, rpoB, rpoC1, and rpoC2 coding for alpha, beta, beta', and beta" RNA polymerase subunits that are homologous to the alpha, beta, and beta' subunits that constitute the core moiety of RNA polymerase in bacteria. However, genes with homology to sigma subunits in bacteria have not been found in plastid genomes. An antibody directed against the principal sigma subunit of RNA polymerase from the cyanobacterium Anabaena sp. PCC 7120 was used to probe western blots of purified chloroplast RNA polymerase from maize, rice, Chlamydomonas reinhardtii, and Cyanidium caldarium. Chloroplast RNA polymerase from maize and rice contained an immunoreactive 64-kD protein. Chloroplast RNA polymerase from C. reinhardtii contained immunoreactive 100- and 82-kD proteins, and chloroplast RNA polymerase from C. caldarium contained an immunoreactive 32-kD protein. The elution profile of enzyme activity of both algal chloroplast RNA polymerases coeluted from DEAE with the respective immunoreactive proteins, indicating that they are components of the enzyme. These results provide immunological evidence for sigma-like factors in chloroplast RNA polymerase in higher plants and algae.
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PMID:Evidence that sigma factors are components of chloroplast RNA polymerase. 815 91

The frxC gene, which is found in chloroplast DNA (ctDNA) and in cyanobacteria, encodes a protein that is required for the light-independent reduction of protochlorophyllide (Pchlide) to chlorophyllide a (Chlide). A DNA fragment downstream of frxC in the filamentous cyanobacterium Plectonema boryanum was cloned and analyzed. Sequencing of the DNA fragment revealed an open reading frame (ORF) that encoded a protein of 467 amino acid residues (designated ORF467), which showed extensive homology to the proteins encoded by genes on ctDNAs (ORF465 in liverwort, gidA in pine and chlN in Chlamydomonas reinhardtii) and to ORF469 protein of the cyanobacterium Synechocystis sp. strain PCC 6803. We isolated a targeted mutant YFM6D-3 in which ORF467 was inactivated by the insertion of a kanamycin-resistance gene into the coding region. YFM6D-3 exhibited a phenotype similar to that of YFC1004, an frxC-disrupted mutant, which did not synthesize chlorophyll (Chl) and accumulated Pchlide, a precursor to Chl, in the dark. These phenotypic characteristics of YFM6D-3 indicate that the light-independent reduction of Pchlide requires not only the FrxC protein but also the ORF467 protein. The amino acid sequences of the homologues of ORF467 exhibit low but significant similarity to those of the alpha and beta subunits of nitrogenase MoFe-protein, suggesting a phylogenetic relationship between the light-independent Pchlide reductase and nitrogenase, as is observed between the FrxC protein and the Fe-protein of nitrogenase.
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PMID:Identification of a nifDK-like gene (ORF467) involved in the biosynthesis of chlorophyll in the cyanobacterium Plectonema boryanum. 819 75

PsbI is a small, integral membrane protein component of photosystem II (PSII), a pigment-protein complex in cyanobacteria, algae and higher plants. To understand the function of this protein, we have isolated the psbI gene from the unicellular cyanobacterium Synechocystis sp. PCC 6803 and determined its nucleotide sequence. Using an antibiotic-resistance cartridge to disrupt and replace the psbI gene, we have created mutants of Synechocystis 6803 that lack the PsbI protein. Analysis of these mutants revealed that absence of the PsbI protein results in a 25-30% loss of PSII activity. However, other PSII polypeptides are present in near wild-type amounts, indicating that no significant destabilization of the PSII complex has occurred. These results contrast with recently reported data indicating that PsbI-deficient mutants of the eukaryotic alga Chlamydomonas reinhardtii are highly light-sensitive and have a significantly lower (80-90%) titer of the PSII complex. In Synechocystis 6803, PsbI-deficient cells appear to be slightly more photosensitive than wild-type cells, suggesting that this protein, while not essential for PSII biogenesis or function, plays a role in the optimization of PSII activity.
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PMID:Directed inactivation of the psbI gene does not affect photosystem II in the cyanobacterium Synechocystis sp. PCC 6803. 854 27

The site-directed mutants of negative patches on silene plastocyanin (PC) were used to investigate the change of interactions between photosystem I (PSI) and PC during the course of evolution from cyanobacteria to plants. The net charges of two highly conserved negative patches (#42-45 and #59-61) on silene PC were systematically modified from -4 to +1. PSI complexes from cucumber and Chlamydomonas reinhardtii were efficient electron acceptors for silene PC. The increase of net charge on the negative patch (#42-45) of silene PC decreased the reduction rates of PSI from cucumber and Chlamydomonas, while the modification of the other negative patch (#59-61) had no effect. Though the addition of MgCl2 decreased the reduction rate of cucumber PSI, the decrease was severely diminished in the case of Chlamydomonas PSI, and the reduction rate increased with increasing concentration of MgCl2 when the net charge of the negative patch (#42-45) was modified to +1. The PSI complexes from Anabaena variabilis and Synechosystis sp. PCC 6803 were inefficient electron acceptors for silene PC and their rates were almost independent of the net charge of the negative patches, as well as the ionic strength of the reaction mixtures. Silene PC specifically cross-linked to the PsaF subunit of PSI complexes from cucumber, Chlamydomonas, Anabaena, and Synechosystis sp. PCC 6803. Modification of the negative patch (#42-45) inhibited the formation of cross-linked adducts in all the cases examined, whereas modification of the other negative patch (#59-61) had essentially no effect. Based on these results, the changes of electrostatic interactions between PC and PSI during the course of evolution from cyanobacteria to plants are discussed.
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PMID:Kinetic and cross-linking studies on the interactions of negative patch mutant plastocyanin from Silene pratensis with photosystem I complexes from cyanobacteria, green algae, and plants. 890 21

A gene (designated ecaA) encoding a vertebrate-like (alpha-type) carbonic anhydrase (CA) has been isolated from two disparate cyanobacteria, Anabaena sp. strain PCC 7120 and Synechococcus sp. strain PCC 7942. The deduced amino acid sequences correspond to proteins of 29 and 26 kDa, respectively, and revealed significant sequence similarity to human CAI and CAII, as well as Chlamydomonas CAHI, including conservation of most active-site residues identified in the animal enzymes. Structural similarities between the animal and cyanobacterial enzymes extend to the levels of antigenicity, as the Anabaena protein cross-reacts with antisera derived against chicken CAII. Expression of the cyanobacterial ecaA is regulated by CO2 concentration and is highest in cells grown at elevated levels of CO2. Immunogold localization using an antibody derived against the ecaA protein indicated an extracellular location. Preliminary analysis of Synechococcus mutants in which ecaA has been inactivated by insertion of a drug resistance cassette suggests that extracellular carbonic anhydrase plays a role in inorganic-carbon accumulation by maintaining equilibrium levels of CO2 and HCO3- in the periplasm.
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PMID:Identification and characterization of a gene encoding a vertebrate-type carbonic anhydrase in cyanobacteria. 900 32

Nuclear genes play important regulatory roles in the biogenesis of the photosynthetic apparatus of eukaryotic cells by encoding factors that control steps ranging from chloroplast gene transcription to post-translational processes. However, the identities of these genes and the mechanisms by which they govern these processes are largely unknown. By using glass bead-mediated transformation to generate insertional mutations in the nuclear genome of Chlamydomonas reinhardtii, we have generated four mutants that are defective in the accumulation of the cytochrome b6f complex. One of them, strain abf3, also fails to accumulate holocytochrome c6. We have isolated a gene, Ccs1, from a C. reinhardtii genomic library that complements both the cytochrome b6f and cytochrome c6 deficiencies in abf3. The predicted protein product displays significant identity with Ycf44 from the brown alga Odontella sinensis, the red alga Porphyra purpurea, and the cyanobacterium Synechocystis strain PCC 6803 (25-33% identity). In addition, we note limited sequence similarity with ResB of Bacillus subtilis and an open reading frame in a homologous operon in Mycobacterium leprae (11-12% identity). On the basis of the pleiotropic c-type cytochrome deficiency in the ccs1 mutant, the predicted plastid localization of the protein, and its relationship to candidate cytochrome biosynthesis proteins in Gram-positive bacteria, we conclude that Ccs1 encodes a protein that is required for chloroplast c-type holocytochrome formation.
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PMID:Ccs1, a nuclear gene required for the post-translational assembly of chloroplast c-type cytochromes. 939 19

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