Salt-dependent expression of glucosylglycerol-phosphate synthase, involved in osmolyte synthesis in the cyanobacterium Synechocystis sp. strain PCC 6803

The cyanobacterium Synechocystis sp. strain PCC 6803 is able to acclimate to levels of salinity ranging from freshwater to twice the seawater concentrations of salt by accumulating the compatible solute glucosylglycerol (GG). Expression of the ggpS gene coding for the key enzyme (glucosylglycerol-phosphate synthase) in GG synthesis was examined in detail. Under control conditions, the GgpS protein is stable, so that weak constitutive transcription of the ggpS gene resulted in a significant protein content. However, the enzyme activity was biochemically switched off, and no GG was detectable. After a salt shock, an immediate increase in mRNA content proportional to the salt content occurred, while the GgpS protein and GG contents rose in a linear manner. Furthermore, the stability of the ggpS mRNA increased transiently. In salt-acclimated cells expression of the ggpS gene, the GgpS protein content, and the amount of accumulated GG depended linearly on the external salt concentration. Mapping of the 5' end of the ggpS transcript revealed a long nontranslated 5' sequence and a putative typical cyanobacterial promoter, which did not show any obvious salt-regulatory element. The alternative sigma factor sigma(F) was found to be involved in salt-dependent regulation of ggpS, since in a sigma(F) mutant induction of this gene was strongly reduced. The present study demonstrated that in addition to biochemical regulation of GgpS activity, alterations of ggpS expression are involved in regulation of GG synthesis in Synechocystis sp. strain PCC 6803. A model showing the interaction of the two regulatory levels is presented.

The Slr0924 protein of Synechocystis sp. strain PCC 6803 resembles a subunit of the chloroplast protein import complex and is mainly localized in the thylakoid lumen

An isolated 25 kDa protein of Synechocystis sp. PCC 6803 was N-terminally sequenced and assigned to a protein encoded by the ORF slr0924. This ORF shows a certain degree of sequence similarity to a subunit from the protein Translocon at the Inner envelope of pea Chloroplasts (Tic22). The deduced amino acid sequence of Slr0924 has a N-terminal extension, that contains two possible translational start points and two possible cleavage sites for leader peptidases. Immunostaining with an antibody raised to the over-produced protein revealed two cross-reacting forms, which probably correspond to a larger intermediate and the mature protein. Immunogold labelling of thin sections showed that the protein is located mainly in the thylakoid region. This result was verified by thylakoid membrane fractionation indicating that Slr0924 is a lumenal protein. The slr0924 gene product is essential for the viability of Synechocystis sp. PCC 6803 as shown by interposon mutagenesis. The merodiploid strain showed reduced photosynthetic activity compared to the wild-type. Furthermore, growth of the merodiploid strain was found to be completely inhibited after cultivation with glucose. Accordingly, the amount of the slr0924 gene product was regulated by glucose and light intensities in wild-type cells. The potential function of the protein in Synechocystis sp. PCC 6803 will be discussed.

Functional analysis of the Na+/H+ antiporter encoding genes of the cyanobacterium Synechocystis PCC 6803

The role of putative Na+/H+ antiporters encoded by nhaS1 (slr1727), nhaS3 (sll0689), nhaS4 (slr1595), and nhaS5 (slr0415) in salt stress response and internal pH regulation of the cyanobacterium Synechocystis PCC 6803 was investigated. For this purpose the mutants (single, double, and triple) impaired in genes coding for Na+/H+ antiporters were constructed using the method of interposon mutagenesis. PCR analyses of DNA demonstrated that mutations in nhaS1, nhaS4, and nhaS5 genes were segregated completely and the mutants contained only inactivated copies of the corresponding genes. Na+/H+ antiporter encoded by nhaS3 was essential for viability of Synechocystis since no completely segregated mutants were obtained. The steady-state intracellular sodium concentration and Na+/H+ antiporter activities were found to be the same in the wild type and all mutants. No differences were found in the growth rates of wild type and mutants during their cultivation in liquid media supplemented with 0.68 M or 0.85 M NaCl as well as in media buffered at pH 7.0, 8.0, or 9.0. The expression of genes coding for Na+/H+ antiporters was studied. No induction of any Na+/H+ antiporter encoding gene expression was found in wild type or single mutant cells grown under high salt or at different pH values. Nevertheless, in cells of double and triple mutants adapted to high salt or alkaline pH some of the remaining Na+/H+ antiporter encoding genes showed induction. These results might indicate that some of Na+/H+ antiporters can functionally replace each other under stress conditions in Synechocystis cells lacking the activity of more than one antiporter.

Identification of genes essential for growth at high salt concentrations using salt-sensitive mutants of the cyanobacterium Synechocystis sp. strain PCC 6803

A collection of 17 salt-sensitive mutants of the cyanobacterium Synechocystis sp. strain PCC 6803 was obtained by random cartridge mutagenesis. The genes coding for proteins essential for growth at high salt concentrations were mapped on the completely known genome sequence of this strain. The two genes coding for enzymes involved in biosynthesis of the osmolyte glucosylglycerol were affected in nine mutants. Two mutants defective in a glycoprotease encoding gene gcp showed a reduced salt resistance. Four genes were identified not previously known to be essential for salt tolerance in cyanobacteria. These genes (slr1799, slr1087, sll1061, and sll1062) code for proteins not yet functionally characterized.

Detection of the isiA gene across cyanobacterial strains: potential for probing iron deficiency

The use of isiA expression to monitor the iron status of cyanobacteria was investigated. Studies of laboratory cultures of the cyanobacterium Synechocystis sp. strain PCC 6803 showed that isiA expression is dependent on the organism's response to iron deficiency; isiA expression starts as soon as a decline in the rate of growth begins. isiA expression is switched on at concentrations of iron citrate of less than 0.7 microM. A PCR method was developed for the specific amplification of the iron-regulated isiA gene from a variety of cyanobacteria. After we developed degenerate primers, 15 new internal isiA fragments (840 bp) were amplified, cloned, and sequenced from strains obtained from algal collections, from new isolates, and from enriched field samples. Furthermore, isiA expression could be detected by means of reverse transcription-PCR when enriched field samples were exposed to restricted iron availability. These results imply that determining the level of iron-regulated isiA expression can serve to indicate iron deficiency in cyanobacterial samples of differing origins from the field.

Biochemical characterization of glucosylglycerol-phosphate synthase of Synechocystis sp. strain PCC 6803: comparison of crude, purified, and recombinant enzymes

Glucosylglycerol-phosphate synthase (GGPS), the key enzyme of the glucosylglycerol biosynthesis in salt-stressed cells of Synechocystis, was biochemically analyzed in crude extracts, after partial purification by FPLC and after overexpression of the gene ggpS in Escherichia coli and purification to homogenity of the recombinant protein, respectively. These GGPS preparations behaved similarly with regard to temperature stability, pH optimum, Mg2+ dependence, inhibition by phosphates, and Km values, but differed in their dependence on NaCl concentration: crude enzyme needed activation by addition of NaCl, whereas both partially-purified and recombinant GGPS showed high activities independent of the NaCl concentration.

Search for three-nucleon force effects in analyzing powers for p-->d elastic scattering

A series of measurements have been performed at KVI to obtain the vector analyzing power A(y) of the (2)H(p-->,pd) reaction as a function of incident beam energy at energies of 120, 135, 150, and 170 MeV. For all these measurements, a range of theta(c.m.) from 30 degrees to 170 degrees has been covered. The purpose of these investigations is to observe possible spin-dependent effects beyond two-nucleon forces. When compared to the predictions of Faddeev calculations, based on two-nucleon forces only, significant deviations are observed at all energies and at center-of-mass angles between 70 degrees and 130 degrees. The addition of present-day three-nucleon forces does not improve the description of the data, demonstrating the still insufficient understanding of the properties of three-nucleon systems.

The iron-regulated isiA gene of Fischerella muscicola strain PCC 73103 is linked to a likewise regulated gene encoding a Pcb-like chlorophyll-binding protein

The expression of the chlorophyll a-binding, iron stress-induced protein IsiA is part of the cyanobacterial response to iron deficiency. A new isiA gene from the filamentous heterocystous cyanobacterial strain, Fischerella muscicola PCC 73103, was identified using standard and inverse PCR. While in unicellular cyanobacterial strains isiA is organized in an operon with isiB (encoding flavodoxin), in Fischerella not an isiB gene but another chlorophyll-binding protein encoding gene was identified downstream of isiA, which shows significant similarities to Pcb-like protein encoding genes known from prochlorophytes. The expression of both genes was clearly activated under iron deficiency. Although isiA and pcbC were independently transcribed, the size of the pcbC transcript indicates a large iron-regulated operon. Beside a 10-fold increase of isiA transcript content iron-starved cells of Fischerella showed a blue-shift in the red chlorophyll a absorption peak. In addition, chlorophyll fluorescence at 77 K was dominated by an emission peak at 685 nm. These features are in accordance with the characteristics of IsiA accumulation in iron-starved unicellular cyanobacteria, suggesting identical IsiA function in heterocystous strains in spite of different genetic organization.

Stress responses of Synechocystis sp. strain PCC 6803 mutants impaired in genes encoding putative alternative sigma factors

In the complete genome sequence of the cyanobacterium SYNECHOCYSTIS: sp. strain PCC 6803 [Kaneko et al. (1996 ). DNA Res 3, 109-136] genes were identified encoding putative group 3 sigma-factors SigH (Sll-0856), SigG (Slr-1545) and SigF (Slr-1564) and the regulatory protein RsbU (Slr-2031). Mutations in these genes were generated by interposon mutagenesis to study their importance in stress acclimation. For the genes sigH, sigF and rsbU, the loci segregated completely. However, attempts to mutagenize the sigG locus resulted in merodiploids. Under standard growth conditions only minor differences were detected between the mutants and wild-type. However, cells of the RsbU mutant showed a clear defect in regenerating growth after a nitrogen- and sulphur-starvation-induced stationary phase. After applying salt, heat and high-light shocks, stress protein synthesis was analysed by means of one- and two-dimensional electrophoresis. Cells of the SigF mutant showed a severe defect in the induction of salt stress proteins. Although the acclimation to moderate salt stress up to 684 mM NaCl was not significantly changed in this mutant, its ability to acclimate to higher concentrations of NaCl was reduced. Northern blot experiments showed a constitutive expression of the rsbU and sigF genes. The expression of the sigH gene was found to be stress-stimulated, particularly in heat-shocked cells, whilst that of sigG was transiently decreased under stress conditions. Possible functions of these regulatory proteins in stress acclimation of Synechocystis cells are discussed.

Molecular analysis of the ggtBCD gene cluster of Synechocystis sp. strain PCC6803 encoding subunits of an ABC transporter for osmoprotective compounds

Genes encoding a substrate-binding protein (ggtB) and two integral membrane proteins (ggtC and ggtD) of the binding-protein-dependent ABC transporter for glucosylglycerol were identified in the genome of Synechocystis sp. strain PCC6803. These genes are clustered on the chromosome about 220 kb away from the previously identified ggtA gene, which encodes the ATP-binding protein of this transport system. The deduced amino acid sequences show significant similarities to corresponding subunits of ABC transporters mediating uptake of maltose and other di- and oligosaccharides in bacteria and archaea. Mutants were constructed by inserting an aphII gene cassette into the coding region of the ggtB, ggtC and ggtD genes. These mutants lost the ability to take up glucosylglycerol, sucrose and trehalose, proving that these compounds are transported by the same system. A truncated ggtB gene lacking the putative signal-peptide-encoding sequence was expressed in Escherichia coli yielding a histidine-tagged soluble protein. The recombinant GgtB protein bound glucosylglycerol with a KD of 0.45 microM and exhibited a somewhat lower affinity towards sucrose and a substantially lower affinity towards trehalose. Transcript analysis by RT-PCR indicated that the genes of the ggtBCD gene cluster form an operon. The transcript level estimated by RNA slot blot analysis using a ggtC-specific probe was very low in cells grown in basal medium but increased significantly after a salt shock.

Proteomics of Synechocystis sp. strain PCC 6803. Identification of periplasmic proteins in cells grown at low and high salt concentrations

Periplasmic proteins isolated by cold osmotic shock of Synechocystis sp. PCC 6803 cells were identified using 2D PAGE, MS and genome analysis. Most of the periplasmic proteins represent 'hypothetical proteins' with unknown function. A number of proteases of different specificity, and several enzymes involved in cell wall biosynthesis were also found. In salt-adapted cells, six proteins were greatly enhanced and three proteins were newly induced. Most of the salt-enhanced proteins are involved in the alteration of cell wall structure of salt-adapted cells. The precursors of all 57 periplasmic proteins identified have a signal peptide; 47 of them contain a typical Sec-dependent signal peptide, whereas 10 contain a putative twin-arginine signal peptide.

Construction of promoter probe vectors for Synechocystis sp. PCC 6803 using the light-emitting reporter systems Gfp and LuxAB

Two promoter probe vectors were constructed for the cyanobacterium Synechocystis sp. strain PCC 6803 using reporter genes, which can be easily detected and quantified in vivo by the ability of their encoded proteins to emit light. The vectors allow the transcriptional fusion of promoter sequences with the gfp and luxAB genes, respectively, and their stable integration into a neutral site of the Synechocystis chromosome. Functionality of these vectors was demonstrated by cloning the promoter of the isiAB operon into both promoter probe vectors and analyzing the stress-dependent emission of light by the obtained reporter strains. As was found before for the isiAB operon, the P(isiAB) reporter gene fusions were induced by iron starvation and high salt stress. Induction rates of mRNA of the wild type operon and the reporter gene fusions were found to be essentially the same, indicating that a promoter fragment containing all necessary regulatory elements has been cloned. However, using the gfp gene a slow increase of protein and fluorescence was found, while the luxAB reporter gene constructs led to a rapid increase in luminescence. The same was found after retransfer of cells back into control media, in which the Gfp protein disappeared slowly, while the LuxAB-based luminescence decreased rapidly. These experiments show that both reporter genes can be used in Synechocystis: the luxAB system seems to be favourable regarding reaction time, while the gfp system has the advantage of being independent from any substrate.

Identification of salt-regulated genes in the genome of the cyanobacterium Synechocystis sp. strain PCC 6803 by subtractive RNA hybridization

To identify genes transcribed preferentially under salt stress, a subtractive RNA hybridization procedure was applied to the cyanobacterium Synechocystis sp. PCC 6803. The screening of a genomic library led to the identification of several RNA species that were more abundant in salt-stressed cells than in control cells. Salt-dependent transcription of the identified genes was verified in Northern blot experiments. In addition to the previously characterized genes cpn60 (encoding GroEL; a molecular chaperone) and isiA (encoding a chlorophyll-binding protein), genes encoding a protein of unknown function (slr0082) and a putative RNA helicase (slr0083) were identified as salt-regulated genes in Synechocystis. Genes slr0082 and slr0083, located at sites adjacent to each other on the Synechocystis chromosome, were transcribed from separate promoters and showed the most significant induction 1-3 h after salt shock. The salt-regulated promoters of these two genes were mapped. Genes cpn60, slr0082, and slr0083 were also found to be induced by a cold shock. The possible role of the identified gene products for salt adaptation of Synechocystis is discussed.

Expression of the ggpS gene, involved in osmolyte synthesis in the marine cyanobacterium Synechococcus sp. Strain PCC 7002, revealed regulatory differences between this strain and the freshwater strain Synechocystis sp. Strain PCC 6803

Synthesis of the osmolyte glucosylglycerol (GG) in the marine cyanobacterium Synechococcus sp. strain PCC 7002 was characterized. The ggpS gene, which encodes the key enzyme (GG-phosphate synthase [GgpS]) in GG biosynthesis, was cloned by using PCR. A 2,030-bp DNA sequence which contained one open reading frame (ORF) was obtained. The protein deduced from this ORF exhibited 85% similarity to the GgpS of the freshwater cyanobacterium Synechocystis sp. strain PCC 6803. The function of the protein was confirmed by generating a ggpS null mutant, which was not able to synthesize GG and thus exhibited a salt-sensitive phenotype. Expression of the ggpS gene was analyzed in salt-shocked cells by performing Northern blot and immunoblot experiments. While almost no expression was detected in cells grown in low-salt medium, immediately after a salt shock the amounts of ggpS mRNA and GgpS protein increased up to 100-fold. The finding that salt-induced expression occurred was confirmed by measuring enzyme activities, which were negligible in control cells but clearly higher in salt-treated Synechococcus sp. cells. The salt-induced increase in GgpS activity could be inhibited by adding chloramphenicol, while in protein extracts of the freshwater cyanobacterium Synechocystis sp. strain PCC 6803 a constitutive, high level of enzyme activity that was not affected by chloramphenicol was found. A comparison of GG accumulation in the two cyanobacteria revealed that in the marine strain osmolyte synthesis seemed to be regulated mainly by transcriptional control, whereas in the freshwater strain control seemed to be predominantly posttranslational.

Isolation of salt-induced periplasmic proteins from Synechocystis sp. strain PCC 6803

Periplasmic proteins were obtained from control cells and salt-adapted cells of the cyanobacterium Synechocystis sp. PCC 6803 using the method of cold osmotic shock. Two of these proteins (PP 1, apparent mol. mass 27.6 kDa, and PP 3, apparent mol. mass 39.9 kDa) were accumulated in high amounts in the periplasm of salt-adapted cells, while the major periplasmic protein (PP 2, apparent mol. mass 36.0 kDa) was accumulated independently from salt. After isolation from gels and partial sequencing, the proteins could be assigned to proteins deduced from the complete genome sequence of Synechocystis. Neither salt-induced periplasmic proteins (PP 1, Slr0924 and PP 3, Slr1485) exhibited sequence similarity to proteins of known function from databases. The major protein (PP 2-Slr0513) showed significant sequence similarities to iron-binding proteins. All proteins included typical leader sequences at their N-terminus.

Screening of patients with Turner syndrome for "hidden" Y-mosaicism

The presence of Y-chromosomal sequences in the cells of patients with Turner-Syndrome (TS) is a risk factor for the development of gonadal tumors. Therefore and since demonstration of Y-material usually results in prophylactic gonadectomy optimal sensitivity and specificity of the diagnosis have to be attempted. We wanted to evaluate the diagnostic potential of cytogenetic investigations as routinely employed in TS. In the most comprehensive study published so far we screened 208 TS patients for the presence of Y-chromosomal sequences by polymerase chain reaction (PCR) specific for eight different loci along the Y-chromosome. Six patients (3%) without cytogenetic evidence of Y-chromosome were found to be Y-positive. Among 12 cases with marker chromosomes two more Y-chromosomal fragments were identified. Thus, PCR-screening for Y-specific sequences was shown to be a valuable tool in the clinical management of Turner patients.

Transcriptional analysis of the isiAB operon in salt-stressed cells of the cyanobacterium Synechocystis sp. PCC 6803

Expression of the isiA and isiB genes was analysed in the cyanobacterium Synechocystis sp. PCC 6803 grown in high salt or in iron-deficient medium. The detection of a 2.3-knt transcript in Northern blot experiments indicated cotranscription of isiAB in an operon, which was confirmed by reverse transcriptase PCR. The abundance of a monocistronic 1.25-knt isiA-specific mRNA was about 10-fold higher than the dicistronic message. The isiAB-specific transcripts were most abundant in cells adapted to 342 mM NaCl and under iron deficiency. The promoter of the operon was mapped to 211 bp upstream of the translational start. A putative Fur binding site was detected immediately upstream of the GTG start codon. A preliminary transcript of about 0.2 knt was detected in cells grown in conditions in which the isiAB operon was not transcribed. This indicates that a repressor binds to the identified Fur binding site and thus inhibits isiAB transcription under low salt and iron replete conditions.

Molecular analysis of the coronavirus-receptor function of aminopeptidase N

Aminopeptidase N (APN) is a major cell surface for coronaviruses of the serogroup I. By using chimeric APN proteins assembled from human, porcine and feline APN we have identified determinants which are critically involved in the coronavirus-APN interaction. Our results indicate that human coronavirus 229E (HCV 229E) is distinct from the other serogroup I coronaviruses in that determinants located within the N-terminal parts of the human and feline APN proteins mediate the infection of HCV 229E, whereas determinants located within the C-terminal parts of porcine, feline and canine APN mediate the infection of transmissible gastro-enteritis virus (TGEV), feline infectious peritonitis virus (FIPV) and canine coronavirus (CCV), respectively. A further analysis of the mapped amino acid segments by site directed mutagenesis revealed that a short stretch of 8 amino acids in the hAPN protein plays a decisive role in mediating HCV 229E reception.

Transcriptional analysis and mutation of a dnaA-like gene in Synechocystis sp. strain PCC 6803

Transcription of the dnaA gene of the cyanobacterium Synechocystis sp. strain PCC 6803 is light dependent and yields a monocistronic mRNA, as determined by Northern analysis. Surprisingly, mutants with inactivated dnaA were viable. In batch cultures under standard conditions, the mutants grew like the wild type and did not show an aberrant phenotype. We conclude that, unlike the situation in other bacteria, dnaA of Synechocystis sp. cannot have an essential function, such as initiation of DNA replication.

The ggpS gene from Synechocystis sp. strain PCC 6803 encoding glucosyl-glycerol-phosphate synthase is involved in osmolyte synthesis

A salt-sensitive mutant of Synechocystis sp. strain PCC 6803 defective in the synthesis of the compatible solute glucosylglycerol (GG) was used to search for the gene encoding GG-phosphate synthase (GGPS), the key enzyme in GG synthesis. Cloning and sequencing of the mutated region and the corresponding wild-type region revealed that a deletion of about 13 kb occurred in the genome of mutant 11. This deletion affected at least 10 open reading frames, among them regions coding for proteins showing similarities to trehalose (otsA homolog)- and glycerol-3-phosphate-synthesizing enzymes. After construction and characterization of mutants defective in these genes, it became obvious that an otsA homolog (sll1566) (T. Kaneko et al., DNA Res. 3:109-136, 1996) encodes GGPS, since only the mutant affected in sll1566 showed salt sensitivity combined with a complete absence of GG accumulation. Furthermore, the overexpression of sll1566 in Escherichia coli led to the appearance of GGPS activity in the heterologous host. The overexpressed protein did not show the salt dependence that is characteristic for the GGPS in crude protein extracts of Synechocystis.

A DNA fragment from the cyanobacterium Synechocystis sp. PCC 6803 mediates gene expression inducible by osmotic stress in E. coli

Fragments of Synechocystis-DNA driving salt-induced gene expression in E. coli were isolated with translational fusions to a 'lacZ gene. One fragment (fragment 19) showed a NaCl-dependent activation of betaGal expression with the maximum of a ninefold increase in enzyme activity. A similar induction was triggered by the nonionic osmolyte sucrose, indicating an osmotically dependent activation. On the contrary, transcriptional activity of the DNA fragment 19 was only slightly enhanced under salt stress conditions, suggesting a posttranscriptional mechanism of induction. Primer extension assay was performed to identify the transcription initiation site. Upstream regions share weak homology to the "-10" hexamer consensus of E. coli sigma70 promoters. The most thermodynamically stable secondary structure for the nontranslated part of the mRNA indicated that potential translation initiation sites might be blocked, leading to a low basal translation, whereas osmotic stress-induced changes of mRNA structure could be involved to increase translation. In order to analyze the function of fragment 19 in Synechocystis, promoter-probe plasmids were constructed allowing the stable integration of transcriptional and translational reporter gene fusions into the cyanobacterial chromosome. Quantitative assessment of reporter gene expression revealed a weak constitutive promoter activity of fragment 19 in Synechocystis. Sequence analysis showed that fragment 19 comprises 223 bp of the ORF sll0747 of the Synechocystis genome.

The cyanobacterium Synechocystis sp. strain PCC 6803 expresses a DNA methyltransferase specific for the recognition sequence of the restriction endonuclease PvuI

By use of restriction endonucleases, the DNA of the cyanobacterium Synechocystis sp. strain PCC 6803 was analyzed for DNA-specific methylation. Three different recognition sites of methyltransferases, a dam-like site including N6-methyladenosine and two other sites with methylcytosine, were identified, whereas no activities of restriction endonucleases could be detected in this strain. slr0214, a Synechocystis gene encoding a putative methyltransferase that shows significant similarities to C5-methylcytosine-synthesizing enzymes, was amplified by PCR and cloned for further characterization. Mutations in slr0214 were generated by the insertion of an aphII gene cassette. Analyses of chromosomal DNAs of such mutants demonstrated that the methylation pattern was changed. The recognition sequence of the methyltransferase was identified as 5'-CGATCG-3', corresponding to the recognition sequence of PvuI. The specific methyltransferase activity was significantly reduced in protein extracts obtained from mutant cells. Mutation of slr0214 also led to changed growth characteristics of the cells compared to wild-type cells. These alterations led to the conclusion that the methyltransferase Slr0214 might play a regulatory role in Synechocystis. The Slr0214 protein was also overexpressed in Escherichia coli, and the purified protein demonstrated methyltransferase activity and specificity for PvuI recognition sequences in vitro. We propose the designation M.Ssp6803I [corrected] (Synechocystis methyltransferase I) for the slr0214-encoded enzyme.

Mutation of a gene encoding a putative glycoprotease leads to reduced salt tolerance, altered pigmentation, and cyanophycin accumulation in the cyanobacterium Synechocystis sp. strain PCC 6803

The salt-sensitive mutant 549 of the cyanobacterium Synechocystis sp. strain PCC 6803 was genetically and physiologically characterized. The mutated site and corresponding wild-type site were cloned and partially sequenced. The genetic analysis revealed that during the mutation about 1.8 kb was deleted from the chromosome of mutant 549. This deletion affected four open reading frames: a gcp gene homolog, the psaFJ genes, and an unknown gene. After construction of mutants with single mutations, only the gcp mutant showed a reduction in salt tolerance comparable to that of the initial mutant, indicating that the deletion of this gene was responsible for the salt sensitivity and that the other genes were of minor importance. Besides the reduced salt tolerance, a remarkable change in pigmentation was observed that became more pronounced in salt-stressed cells. The phycobilipigment content decreased, and that of carotenoids increased. Investigations of changes in the ultrastructure revealed an increase in the amount of characteristic inclusion bodies containing the high-molecular-weight nitrogen storage polymer cyanophycin (polyaspartate and arginine). The salt-induced accumulation of cyanophycin was confirmed by chemical estimations. The putative glycoprotease encoded by the gcp gene might be responsible for the degradation of cyanophycin in Synechocystis. Mutation of this gene leads to nitrogen starvation of the cells, accompanied by characteristic changes in pigmentation, ultrastructure, and salt tolerance level.