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PubMed2006

Involvement of DnaK3, one of the three DnaK proteins of cyanobacterium Synechococcus sp. PCC7942, in translational process on the surface of the thylakoid membrane.

The Synechococcus sp. PCC7942 strain carrying a missense mutation in the peptide-binding domain of DnaK3, one of the essential dnaK gene products, revealed temperature-sensitive growth. We also isolated suppressor mutants of this strain. One of the suppressors was mapped in the ribosomal protein gene rpl24 (syc1876), which encodes the 50S ribosomal protein L24. Subcellular localization of three DnaK proteins was determined, and the results indicated that a quantity of DnaK3 was dislocated from membrane-bound polysomes when dnaK3 temperature-sensitive mutant was incubated at non-permissive temperatures. Furthermore, we examined the photosystem II reaction center protein D1 and detected a translational intermediate polypeptide in membrane-bound polysome fractions prepared from dnaK3 temperature-sensitive cells grown at high temperature. These characteristic features of DnaK3 localizations and detection of D1 protein intermediate were not observed in the suppressor mutant even at high temperatures.

Amino Acid Sequence↗

PubMed2007

Protection of psbAII transcript from ribonuclease degradation in vitro by DnaK2 and DnaJ2 chaperones of the cyanobacterium Synechococcus elongatus PCC 7942.

Three dnaK and four dnaJ genes have been identified in the genome of cyanobacterium Synechococcus elongatus PCC 7942. Our comprehensive analysis of yeast two-hybrid screening revealed a specific interaction among DnaK2, DnaJ2, and RNase E, an essential endoribonuclease. We examined the effects of DnaK2 and DnaJ2 on RNase E activity by monitoring the digestion of psbAII transcript in vitro. The addition of DnaK2 and DnaJ2 obviously inhibited RNase E activity in an ATP-dependent manner. These results suggest that DnaK2 and DnaJ2 are involved in RNA degradation through interaction with RNase E.

Bacterial Proteins↗

PubMedDate not supplied

[The gap1 operon of the cyanobacterium Synechococcus PCC 7942 carries a gene encoding glycogen phosphorylase and is induced under anaerobic conditions].

The cloning and sequencing of the gap1 operon, which encodes the glycolytic NAD-specific glyceraldehyde-3-phosphate dehydrogenase in the cyanobacterium Synechococcus PCC 7942, showed that the gap1 gene is closely linked to the glgP gene encoding glycogen phosphorylase (an enzyme that catalyzes the first step of glycogen degradation). Northern blotting experiments showed that the gap1 and glgP genes are co-expressed and organized in a bicistronic operon, whose expression is enhanced under anaerobic conditions. The nucleotide sequence of the operon has been submitted to GenBank under accession number AF428099.

Anaerobiosis↗

PubMedDate not supplied

[The gap3 gene of Synechococcus PCC 7942 is induced during adaptation to low CO2 concentrations].

The gap3 genes of the Synechococcus and Anabaena cyanobacteria fulfill so far unknown function. A homolog of this gene has recently been found in the nuclear genomes of diplonemids, which are heterotrophic flagellates closely related to kinetoplastids and euglenoids. To understand the function of the gap3 gene in the cyanobacteria, we performed Northern blotting experiments with the gap3 probes under different growth conditions. Under the standard photosynthetic growth conditions (high illumination and 1% CO2 in the gas phase), the expression of the gap3 gene was very low, but significantly increased during cell adaptation to the low CO2 concentration (0.03%). The gap3 operon was expressed as a polycistronic transcript of about 7 kb in size, which included ORF2 (1259 bp) immediately downstream of gap3. ORF2 probably encodes a putative transporter of HCO3. The nucleotide sequence of ORF2 has been submitted to GenBank under accession number AF 428100.

Adaptation, Physiological↗

PubMed2004

Computational prediction of operons in Synechococcus sp. WH8102.

We computationally predict operons in the Synechococcus sp. WH8102 genome based on three types of genomic data: intergenic distances, COG gene functions and phylogenetic profiles. In the proposed method, we first estimate a log-likelihood distribution for each type of genomic data, and then fuse these distribution information by a perceptron to discriminate pairs of genes within operons (WO pairs) from those across transcription unit borders (TUB pairs). Computational experiments demonstrated that WO pairs tend to have shorter intergenic distances, a higher probability being in the same COG functional categories and more similar phylogenetic profiles than TUB pairs, indicating their powerful capabilities for operon prediction. By testing the method on 236 known operons of Escherichia coli K12, an overall accuracy of 83.8% is obtained by joint learning from multiple types of genomic data, whereas individual information source yields accuracies of 80.4%, 74.4%, and 70.6% respectively. We have applied this new approach, in conjunction with our previous comparative genome analysis-based approach, to predict 556 (putative) operons in WH8102. All predicted data are available at (http://www.cs.ucr.edu/~xin/operons.htm) for public use.

Computational Biology↗

PubMed2005

[Expression and characterization of FNRD in cyanobacterium Synechococcus sp. PCC 7002].

The petHL genes under the control of Lac and Kan promoters were transformed into Synechococcus sp. PCC 7002, respectively. Both of the petHL genes are integrated into the cyanobacterium chromosomes, which is inferred from the results of Southern blot analysis. Western blot analysis results show that both petHL genes are expressed in the transformed cells, and Kan promoter is more effective than Lac promoter. The FNRD in vivo shows the same stability as that of FNR holoenzyme. Some FNRD molecules are probably acylated as judged by the result of Triton X-114 phase partition test. FNRD in vivo might act as a component in photosynthetic electron transport chain, which increases the photosynthetic oxygen evolution rate.

Blotting, Southern↗

PubMed2006

[Sited-directed mutagenesis of hCu, Zn-SOD gene and its expression in Synechococcus sp. PCC7942].

The Cys111 genetic code of human copper/zinc superoxide dismutase (hCu, Zn-SOD) gene in the pESOD plamid was mutated into the Ala111 code with site-directed mutagenesis, and then the plamid pESODT111 which contained groESL promoter, mutated hCu, Zn-SOD gene, rbcS-polyA terminator and reporter gene (Kanr) was constructed and transduced into Synechococcus sp. PCC7942 with homologous recombination platform. The results of PCR and DNA sequence analysis showed that the target nucleotide had been genetically integrated into genome DNA of the host cell. SDS-PAGE, Western blot and Pyrogallol autoxidation assay confirmed that the transformant strains expressed the mutated hCu, Zn-SOD protein. And the level of the mutated hCu, Zn-SOD protein reached a value of 3.61% of the total soluble protein. Furthermore, the transformants still retained 95% activities of SOD after 30 minutes at 80 degrees C environment, it indicated that the mutated hCu, Zn-SOD protein could endure higher temperature than the natural one.

Blotting, Western↗

PubMed2006

Catalytic and regulatory properties of sulphur metabolizing enzymes in cyanobacterium Synechococcus elongatus PCC 7942.

Synechococcus elongatus PCC 7942 was able to grow with several S sources. The sulphur metabolizing enzymes viz. ATP sulphurylase, cysteine synthase, thiosulphate reductase and L- and D-cysteine desulphydrases were regulated by sulphur sources, particularly by sulphur amino acids and organic sulphate esters. Sulphur starvation reduced ATP sulphurylase and cysteine synthase whereas reduced glutathione appreciated Cys degradation activity. With partially purified enzymes apparent Km values for sulphate, ATP, D- and L-Cys, thiosulphate, sulphide and O-acetyl serine were in a range of 12-50 microM. p-Nitrophenyl sulphate inhibited ATP sulphurylase competitively. Met was a feedback inhibitor of several key enzymes.

Catalysis↗

PubMed2002

Immunocytochemical localization of the stress-induced DpsA protein in the cyanobacterium Synechococcus sp. strain PCC 7942.

Proteins of the Dps family are divergent ferritins that have been shown to bind DNA with high affinity during periods of nutrient and oxidative stress. Such binding protects the chromosome from peroxide attack. Surprisingly, we show by immunocytochemistry that the cyanobacterial Dps homolog, DpsA, localizes preferentially to the thylakoid membrane in Synechococcus sp. strain PCC7942. We propose that two DpsA pools are functioning in this species--an insoluble fraction bound to the chromosome, and a soluble fraction acting as a ferritin involved metal homeostasis of the photosynthetic apparatus. This model is presented in light of recent work on the E. coli Dps protein showing that DNA binding is regulated by the metal-binding capacity of the Dps complex (Frenkiel-Krispin et al. 2001). Additionally, the pattern of DpsA localization in cells as they progress through the growth curve suggests that the DpsA complex may be involved in metal ion transport across the cell envelope.

Amino Acid Sequence↗

PubMed1995

Electron transport regulates exchange of two forms of photosystem II D1 protein in the cyanobacterium Synechococcus.

Synechococcus sp. PCC 7942 modulates photosynthetic function by transiently replacing the constitutive D1 photosystem II protein, D1:1, with an alternate form, D1:2, to help counteract photoinhibition under excess light. We show that a temperature drop from 37 to 25 degrees C also drives D1:1/D1:2 exchange under constant, moderate light. Chilling or light-induced D1 exchange results from rapid loss of psbAI message coding for D1:1 and accumulation of psbAII and psbAIII messages coding for D1:2. During chilling, a large pool of a novel form, D1:2*, transiently accumulates, distinguishable from normal D1 by an increase in apparent molecular mass. D1:2* is not phosphorylated and is probably a functionally inactive, incompletely processed precursor. After acclimation to 25 degrees C, D1:2* disappears and D1:1 again predominates, although substantial D1:2 remains. Partial inhibition of electron transport under constant, moderate light also triggers the D1 exchange process. These treatments all increase excitation pressure on photosystem II relative to electron transport. Therefore, information from photosynthetic electron transport regulates D1 exchange without any requirement for a change in light intensity or quality, possibly via a redox sensing mechanism proximal to photosystem II.

Antioxidants↗

PubMed1994

Identification and characterization of the sec-A protein homologue in the cyanobacterium Synechococcus PCC7942.

The secA gene product mediates protein translocation across the cytoplasmic membrane in Escherichia coli. We have cloned a gene homologous to secA from the genome of the cyanobacterium Synechococcus PCC7942. The deduced amino acid sequence, 948 amino acids long, shows 43% homology with that of the E. coli secA and 47-48% homology with those of the algal plastid secA genes. Upon subcellular fractionation, the cyanobacterial SecA protein was mainly found as soluble homodimer in the cytosol, but the remaining small but distinct fraction was associated with both the cytoplasmic and thylakoid membranes. The SecA protein likely participates in protein translocation across both the cytoplasmic and thylakoid membranes in cyanobacterial cells.

Adenosine Triphosphatases↗

PubMed1994

Identification of dnaK multigene family in Synechococcus sp. PCC7942.

Three dnaK gene homologs have been cloned and sequenced from cyanobacterium Synechococcus sp. PCC7942 using a set of primers designed from two conserved regions of known dnaK genes. This is the first example of triple genes for dnaK from prokaryotic cells. These three genes were derived from different loci of the chromosome.

Bacterial Proteins↗

PubMed1994

Sequence analysis of the third dnaK homolog gene in Synechococcus sp. PCC7942.

The nucleotide sequence of the third dnaK homolog gene from Synechococcus sp. PCC7942 has been determined. Deduced amino acid sequences of dnaK3 and of previously reported dnaK1 and dnaK2 were compared with Hsp70s from various species. Among the three DnaK homologs, DnaK2 shows close relationship to chloroplast proteins and DnaK3 also has some similarities to them. On the other hand, DnaK1 has few chloroplast-specific motifs and forms a deep branch of the prokaryotic cluster in the phylogenetic tree.

Amino Acid Sequence↗

PubMed1996

DnaK3, one of the three DnaK proteins of cyanobacterium Synechococcus sp. PCC7942, is quantitatively detected in the thylakoid membrane.

Subcellular localization of three DnaK proteins of cyanobacterium Synechococcus sp. PCC7942 was determined. DnaK1 and DnaK2 proteins were detected mainly in the cytosolic fraction. On the other hand, the DnaK3 protein occurred in large amounts in the thylakoid membrane fraction. Furthermore, DnaK3 was found to be located on the surface of the thylakoid membrane on the cytosol side. Subcellular localization of chimeric and truncated DnaK3 proteins was also determined, and it was suggested that the region a.a. 381 to a.a. 597 of DnaK3 protein, which is considered to correspond to the peptide-binding domain, was required for the association with the thylakoid membrane.

Bacterial Proteins↗

PubMed1997

Sequence and analysis of a dnaJ homologue gene in cyanobacterium Synechococcus sp. PCC7942.

The chromosomal region containing a dnaJ gene homologue (dnaJ7942) was sequenced from unicellular cyanobacterium Synechococcus sp. PCC7942. The dnaJ7942 gene as well as following two orfs are located in the region immediately downstream of dnaK3, and they seem to be cotranscribed. The dnaJ7942 gene product shares, like all J homologues, homology for the highly conserved "J-domain" of DnaJ. It does not have, however, a glycine and phenylalanine (G/F)-rich region nor cysteine (Cys)-rich region unlike the Escherichia coli DnaJ protein. When this gene was expressed in E. coli, cells became filamentous in contrast to those expressing the E. coli dnaJ gene. Gene disruption experiments indicated that the dnaJ7942 gene was essential for growth. Analysis of subcellular localization revealed that the DnaJ protein is mainly located on the thylakoid membrane in the cyanobacterium.

Amino Acid Sequence↗

PubMed1994

Crystallization and preliminary X-ray analysis of wild-type and K272A mutant glutamate 1-semialdehyde aminotransferase from Synechococcus.

Crystals of the pyridoxal-5'-phosphate dependent enzyme glutamate-1-semialdehyde aminotransferase (EC 5.4.3.8) from Synechococcus have been grown from polyethylene glycol solutions. The wild-type enzyme crystallizes in space group P2(1)2(1)2(1), with cell dimensions a = 68.4 A, b = 108.0 A, c = 122.6 A. The inactive mutant in which the cofactor-binding lysine 272 residue is replaced by alanine (K272A) gives monoclinic crystals of space group P2(1) with cell dimensions a = 67.1 A, b = 108.6 A, c = 124.5 A and beta = 115.7 degrees. These crystal forms diffract to 2.4 A and 2.7 A resolution, respectively.

Crystallization↗

PubMed1996

Highly ordered two-dimensional crystals of photosystem I reaction center from Synechococcus sp.: functional and structural analyses.

The photosystem 1 reaction center complex from the thermophilic cyanobacterium Synechococcus sp. was isolated by Triton X-100 solubilization and fractional precipitation with polyethylene glycol. As shown by gel electrophoresis, the isolated complex was composed of the 83 kDa subunits A and B, and at least six other subunits with molecular mass below 20 kDa. Electron transfer from the primary electron donor P700 to the FA/FB centers was demonstrated by flash-induced absorption change of the isolated complex, while electron paramagnetic resonance (EPR) spectroscopy showed that the complex contained a full set of Fe-S clusters. Isolated complexes were reconstituted into two-dimensional crystals in the presence of phospholipids and different cations. The crystals were found to be active by flash-induced separation and EPR spectroscopy. Electron microscopy and digital image processing of negatively stained and frozen-hydrated specimens revealed orthorhombic crystals with unit cell dimensions a = 138 A, b = 145 A and p12(1) symmetry. A three-dimensional map was calculated for negatively stained crystals to 19 A resolution, whereas the projection map of frozen-hydrated crystals exhibited 8 A resolution.

Crystallization↗

PubMed1997

Solution structure of ferredoxin from the thermophilic cyanobacterium Synechococcus elongatus and its thermostability.

The three-dimensional structure of ferredoxin, purified from the thermophilic cyanobacterium Synechococcus elongatus, was determined in aqueous solution by two-dimensional proton nuclear magnetic resonance. In addition to the 946 distance constraints from nuclear Overhauser effect connectivities, we added 241 distance constraints derived from the crystal structure of Spirulina platensis ferredoxin to the 19 residues close to the [2Fe-2S] iron-sulfur center, where crosspeaks disappeared due to paramagnetic effects. The atomic root-mean-square difference of the ten converged structures from the mean structure was 0.61(+/-0.12) A for backbone atoms (N, C(alpha), C'). The main-chain structure was almost the same as the crystal structures of other mesophile ferredoxins, but comparison of the side-chain structures revealed an extension of the hydrophobic core, a unique hydrophobic patch on the surface of the large beta-sheet, and two unique charge networks in this thermostable ferredoxin structure, some of which might contribute to thermostability.

Amino Acid Sequence↗