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A sudden decrease in ambient temperature induces the expression of a number of genes in poikilothermic organisms. We report here that the cold inducibility of gene expression in Synechocystis sp. PCC 6803 was enhanced by the rigidification of membrane lipids that was engineered by disruption of genes for fatty acid desaturases. DNA microarray analysis revealed that cold-inducible genes could be divided into three groups according to the effects of the rigidification of membrane lipids. The first group included genes whose expression was not induced by cold in wild-type cells but became strongly cold-inducible upon rigidification of membrane lipids. This group included certain heat-shock genes, genes for subunits of the sulfate transport system, and the hik34 gene for a histidine kinase. The second group consisted of genes whose cold inducibility was moderately enhanced by the rigidification of membrane lipids. Most genes in this group encoded proteins of as yet unknown function. The third group consisted of genes whose cold inducibility was unaffected by the rigidification of membrane lipids. This group included genes for an RNA helicase and an RNA-binding protein. DNA microarray analysis also indicated that the rigidification of membrane lipids had no effect on the heat inducibility of gene expression. Hik33, a cold-sensing histidine kinase, regulated the expression of most genes in the second and third groups but of only a small number of genes in the first group, an observation that suggests that the cold-inducible expression of genes in the first group might be regulated by a cold sensor that remains to be identified.
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PMID:Gene-engineered rigidification of membrane lipids enhances the cold inducibility of gene expression in synechocystis. 1250 18

Sucrose-phosphatase (SPP; EC 3.1.3.24) catalyzes the final step in the pathway of sucrose biosynthesis and higher plants contain multiple isoforms of the enzyme encoded by different genes. The genome of the dicotyledonous plant Arabidopsis thaliana (thale cress) contains four SPP-like genes on chromosomes 1 (AtSPP1), 2 (AtSPP2) and 3 (AtSPP3a and AtSPP3b), all of which are expressed. The genome of the monocotyledonous plant rice (Oryza sativa) also contains four SPP-like genes, which have very similar exon-intron structures to those from A. thaliana. Two cDNA clones that encode catalytically active SPP enzymes have been isolated from maize (Zea mays), showing that this species contains at least two functional SPP genes. Multiple SPP-like cDNA clones have also been identified from wheat (Triticum aestivum), barley (Hordeum vulgare) and tomato (Lycopersicon esculentum). The genomes of two cyanobacteria, Synechocystis sp. PCC 6803 and Anabaena sp. PCC 7120, contain single spp genes. The cyanobacterial SPPs and the N-terminal region of the higher plant enzyme share significant similarity with members of the haloacid dehalogenase (HAD) superfamily of hydrolases/phosphatases. In addition to the HAD phosphatase domain, SPP from higher plants also contains a shorter, C-terminal domain of unknown function. An SPP-like sequence from the bryophyte (moss) Physcomitrella patens also contains this C-terminal domain, indicating that its acquisition was an early event in the evolution of higher plants.
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PMID:Sucrose-phosphatase gene families in plants. 1255 80

Arsenic is one of the most important global environmental pollutants. Here we show that the cyanobacterium Synechocystis sp. strain PCC 6803 contains an arsenic and antimony resistance operon consisting of three genes: arsB, encoding a putative arsenite and antimonite carrier, arsH, encoding a protein of unknown function, and arsC, encoding a putative arsenate reductase. While arsB mutant strains were sensitive to arsenite, arsenate, and antimonite, arsC mutants were sensitive only to arsenate. The arsH mutant strain showed no obvious phenotype under the conditions tested. In vivo the arsBHC operon was derepressed by oxyanions of arsenic and antimony (oxidation state, +3) and, to a lesser extent, by bismuth (oxidation state, +3) and arsenate (oxidation state, +5). In the absence of these effectors, the operon was repressed by a transcription repressor of the ArsR/SmtB family, encoded by an unlinked gene termed arsR. Thus, arsR null mutants showed constitutive derepression of the arsBHC operon. Expression of the arsR gene was not altered by the presence of arsenic or antimony compounds. Purified recombinant ArsR protein binds to the arsBHC promoter-operator region in the absence of metals and dissociates from the DNA in the presence of Sb(III) or As(III) but not in the presence of As(V), suggesting that trivalent metalloids are the true inducers of the system. DNase I footprinting experiments indicate that ArsR binds to two 17-bp direct repeats, with each one consisting of two inverted repeats, in the region from nucleotides -34 to + 17 of the arsBHC promoter-operator.
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PMID:Arsenic sensing and resistance system in the cyanobacterium Synechocystis sp. strain PCC 6803. 1294 88

The Synechocystis sp. strain PCC 6803, which has a T192H mutation in the D2 protein of photosystem II, is an obligate photoheterotroph due to the lack of assembled photosystem II complexes. A secondary mutant, Rg2, has been selected that retains the T192H mutation but is able to grow photoautotrophically. Restoration of photoautotrophic growth in this mutant was caused by early termination at position 294 in the Slr2013 protein. The T192H mutant with truncated Slr2013 forms fully functional photosystem II reaction centers that differ from wild-type reaction centers only by a 30% higher rate of charge recombination between the primary electron acceptor, QA-, and the donor side and by a reduced stability of the oxidized form of the redox-active Tyr residue, YD, in the D2 protein. This suggests that the T192H mutation itself did not directly affect electron transfer components, but rather affected protein folding and/or stable assembly of photosystem II, and that Slr2013 is involved in the folding of the D2 protein and the assembly of photosystem II. Besides participation in photosystem II assembly, Slr2013 plays a critical role in the cell, because the corresponding gene cannot be deleted completely under conditions in which photosystem II is dispensable. Truncation of Slr2013 by itself does not affect photosynthetic activity of Synechocystis sp. strain PCC 6803. Slr2013 is annotated in CyanoBase as a hypothetical protein and shares a DUF58 family signature with other hypothetical proteins of unknown function. Genes for close homologues of Slr2013 are found in other cyanobacteria (Nostoc punctiforme, Anabaena sp. strain PCC 7120, and Thermosynechococcus elongatus BP-1), and apparent orthologs of this protein are found in Eubacteria and Archaea, but not in eukaryotes. We suggest that Slr2013 regulates functional assembly of photosystem II and has at least one other important function in the cell.
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PMID:Slr2013 is a novel protein regulating functional assembly of photosystem II in Synechocystis sp. strain PCC 6803. 1459 35

The genome of the unicellular cyanobacterium Synechocystis sp. PCC 6803 consists of a single chromosome and several plasmids of different sizes, and the nucleotide sequences of the chromosome and three small plasmids (5.2 kb, 2.4 kb, and 2.3 kb) have already been sequenced. We newly determined the nucleotide sequences of four large plasmids, which have been identified in our laboratory (pSYSM:120 kb, pSYSX:106 kb, pSYSA:103 kb, and pSYSG:44 kb). Computer-aided analysis was performed to explore the genetic information carried by these plasmids. A total of 397 potential protein-encoding genes were predicted, but little information was obtained about the functional relationship of plasmids to host cell, as a large portion of the predicted genes (77%) were of unknown function. The occurrence of the potential genes on plasmids was divergent, and parA was the only gene common to all four large plasmids. The distribution data of a Cyanobacterium-specific sequence (HIP1: 5'-GCGATCGC-3') suggested that respective plasmids could have originated from different cyanobacterial strains.
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PMID:Structural analysis of four large plasmids harboring in a unicellular cyanobacterium, Synechocystis sp. PCC 6803. 1468 84

In this report, we describe a newly developed method for isolating outer membranes from Synechocystis sp. PCC 6803 cells. The purity of the outer membrane fraction was verified by immunoblot analysis using antibodies against membrane-specific marker proteins. We investigated the protein composition of the outer membrane using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry followed by database identification. Forty-nine proteins were identified corresponding to 29 different gene products. All of the identified proteins have a putative N-terminal signal peptide. About 40% of the proteins identified represent hypothetical proteins with unknown function. Among the proteins identified are a Toc75 homologue, a protein that was initially found in the outer envelope of chloroplasts in pea, as well as TolC, putative porins, and a pilus protein. Other proteins identified include ABC transporters and GumB, which has a suggested function in carbohydrate export. A number of proteases such as HtrA were also found in the outer membrane of Synechocystis sp. PCC 6803.
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PMID:Isolation of outer membrane of Synechocystis sp. PCC 6803 and its proteomic characterization. 1499 Jun 84

Flavodoxins are classified in two groups according to the presence or absence of a approximately 20-residue loop of unknown function. In the accompanying paper (36), we have shown that the differentiating loop from the long-chain Anabaena PCC 7119 flavodoxin is a peripheral structural element that can be removed without preventing the proper folding of the apoprotein. Here we investigate the role played by the loop in the stability and folding mechanism of flavodoxin by comparing the equilibrium and kinetic behavior of the full-length protein with that of loop-lacking, shortened variants. We show that, when the loop is removed, the three-state equilibrium thermal unfolding of apoflavodoxin becomes two-state. Thus, the loop is responsible for the complexity shown by long-chain apoflavodoxins toward thermal denaturation. As for the folding reaction, both shortened and wild type apoflavodoxins display three-state behavior but their folding mechanisms clearly differ. Whereas the full-length protein populates an essentially off-pathway transient intermediate, the additional state observed in the folding of the shortened variant analyzed seems to be simply an alternative native conformation. This finding suggests that the long loop may also be responsible for the accumulation of the kinetic intermediate observed in the full-length protein. Most revealing, however, is that the influence of the loop on the overall conformational stability of apoflavodoxin is quite low and the natively folded shortened variant Delta(120-139) is almost as stable as the wild type protein. The fact that the loop, which is not required for a proper folding of the polypeptide, does not even play a significant role in increasing the conformational stability of the protein supports our proposal (36) that the differentiating loop of long-chain flavodoxins may be related to a recognition function, rather than serving a structural purpose.
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PMID:The long and short flavodoxins: II. The role of the differentiating loop in apoflavodoxin stability and folding mechanism. 1531 17

The light reactions of oxygenic photosynthesis are mediated by multisubunit pigment-protein complexes situated within the specialized thylakoid membrane system. The biogenesis of these complexes is regulated by transacting factors that affect the expression of the respective subunit genes and/or the assembly of their products. Here we report on the analysis of the PratA gene from the cyanobacterium Synechocystis sp. PCC 6803 that encodes a periplasmic tetratricopeptide repeat protein of formerly unknown function. Targeted inactivation of PratA resulted in drastically reduced photosystem II (PSII) content. Protein pulse labeling experiments of PSII subunits indicated that the C-terminal processing of the precursor of the reaction center protein D1 is compromised in the pratA mutant. Moreover, a direct interaction of PratA and precursor D1 was demonstrated by applying yeast two-hybrid analyses. This suggests that PratA represents a factor facilitating D1 maturation via the endoprotease CtpA. The periplasmic localization of PratA supports a model that predicts the initial steps of PSII biogenesis to occur at the plasma membrane of cyanobacterial cells.
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PMID:PratA, a periplasmic tetratricopeptide repeat protein involved in biogenesis of photosystem II in Synechocystis sp. PCC 6803. 1532 51

A highly purified cytochrome b(6)f complex from the cyanobacterium Synechocystis sp. PCC 6803 selectively binds one chlorophyll a and one carotenoid in analogy to the recent published structure from two other b(6)f complexes. The unknown function of these pigments was elucidated by spectroscopy and site-directed mutagenesis. Low-temperature redox difference spectroscopy showed red shifts in the chlorophyll and carotenoid spectra upon reduction of cytochrome b(6), which indicates coupling of these pigments with the heme groups and thereby with the electron transport. This is supported by the correlated kinetics of these redox reactions and also by the distinct orientation of the chlorophyll molecule with respect to the heme cofactors as shown by linear dichroism spectroscopy. The specific role of the carotenoid echinenone for the cytochrome b(6)f complex of Synechocystis 6803 was elucidated by a mutant lacking the last step of echinenone biosynthesis. The isolated mutant complex preferentially contained a carotenoid with 0, 1 or 2 hydroxyl groups (most likely 9-cis isomers of beta-carotene, a monohydroxy carotenoid and zeaxanthin, respectively) instead. This indicates a substantial role of the carotenoid - possibly for strucure and assembly - and a specificity of its binding site which is different from those in most other oxygenic photosynthetic organisms. In summary, both pigments are probably involved in the structure, but may also contribute to the dynamics of the cytochrome b(6)f complex.
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PMID:Functional implications of pigments bound to a cyanobacterial cytochrome b6f complex. 1565 95

We performed comparative and mutational analyses to define more comprehensively the repertoire of genes involved in cyanobacterial cell division. Genes ftsE, ftsI, ftsQ, ftsW, and (previously recognized) ftsZ, minC, minD, minE and sulA were identified as homologues of cell division genes of Gram-negative and Gram-positive bacteria. Transposon mutagenesis of Synechococcus elongatus PCC 7942 identified five additional genes, cdv1, cdv2, cdv3, ftn6 and cikA, involved in cell division. cdv1 encodes a presumptive periplasmic peptidyl-prolyl cis-trans isomerase. cdv2 has similarity to ylmF which, like divIVA, lies within the Gram-positive bacterial ylm gene cluster whose members have functions associated with division. Conservation of other ylm genes in cyanobacteria suggests that cyanobacteria and Gram-positive bacteria share specific division proteins. Two ylm homologues are also found in algal and plant genomes. cdv3 has low but significant similarity to divIVA, suggesting that minE and cdv3 both mediate division-site determination in cyanobacteria. In contrast, Gram-positive bacteria lack minE, and (Gram-negative) proteobacteria lack divIVA. ftn6, of unknown function, and the circadian input kinase, cikA, are specific to cyanobacteria. In S. elongatus, unlike in other bacteria, FtsZ rings are formed at sites occupied by nucleoids. Thus, the division machinery of cyanobacteria differs in its composition and regulation from that of Gram-negative and Gram-positive bacteria.
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PMID:Identification of cyanobacterial cell division genes by comparative and mutational analyses. 1577 84


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