SEARCH · PubMed Health

Results for “Synechococcus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources

PubMed1998

The cyanobacterium Synechococcus resists UV-B by exchanging photosystem II reaction-center D1 proteins.

Current ambient UV-B levels can significantly depress productivity in aquatic habitats, largely because UV-B inhibits several steps of photosynthesis, including the photooxidation of water catalyzed by photosystem II. We show that upon UV-B exposure the cyanobacterium Synechococcus sp. PCC 7942 rapidly changes the expression of a family of three psbA genes encoding photosystem II D1 proteins. In wild-type cells the psbAI gene is expressed constitutively, but strong accumulations of psbAII and psbAIII transcripts are induced within 15 min of moderate UV-B exposure (0.4 W/m2). This transcriptional response causes an exchange of two distinct photosystem II D1 proteins. D1:1 is encoded by psbAI, but on UV-B exposure, it is largely replaced by the alternate D1:2 form, encoded by both psbAII and psbAIII. The total content of D1 and other photosystem II reaction center protein, D2, remained unchanged throughout the UV exposure, as did the content and composition of the phycobilisome. Wild-type cells suffered only slight transient inhibition of photosystem II function under UV-B exposure. In marked contrast, under the same UV-B treatment, a mutant strain expressing only psbAI suffered severe (40%) and sustained inhibition of photosystem II function. Another mutant strain with constitutive expression of psbAII and psbAIII was almost completely resistant to the UV-B treatment, showing no inhibition of photosystem II function and only a slight drop in electron transport. In Synechococcus the rapid exchange of alternate D1 forms, therefore, accounts for much of the cellular resistance to UV-B inhibition of photosystem II activity and photosynthetic electron transport. This molecular plasticity may be an important element in community-level responses to UV-B, where susceptibility to UV-B inhibition of photosynthesis changes diurnally.

Bacterial Proteins↗

PubMed1998

A carboxyl-terminal Cys2/His2-type zinc-finger motif in DNA primase influences DNA content in Synechococcus PCC 7942.

The DNA primase gene, dnaG, has been isolated from the cyanobacterium Synechococcus PCC 7942. It is not part of a macromolecular synthesis operon but is co-transcribed with pheT and located adjacent to the metallothionein divergon, smt. At the carboxyl terminus of this DnaG is a Cys2/His2 zinc-finger motif. The carboxyl-terminal 91 residues bound 65Zn and 0.95 g atom of Zn2+ mol-1 were detected with 4-(2-pyridylazo)resorcinol. Following exposure to Cd2+, 0.95 g atom of Cd2+ was displaced by 2 equivalents of p-(hydroxymercuri) phenylsulfonate mol-1, while only 0.03 g atom of Cd2+ was displaced mol-1 polypeptide missing the carboxyl-terminal (residue 592 onward) zinc-finger motif. Zn2+ caused an increase in intensity, and a reduction in wavelength, of Trp fluorescence at the tip of the predicted zinc-finger, while EDTA caused the converse. Cells containing a single chromosomal codon substitution (C597S), altering the zinc-finger, were generated by exploiting Zn2+-sensitive smt mutants and the proximity of dnaG to smt. Cells in which smt and dnaG(C597S) had integrated into the chromosome were selected via restored Zn2+ tolerance. Synechococcus PCC 7942 and its dnaG(C597S) mutant grew at equivalent rates, but the latter had a reduced number of chromosomes.

Base Sequence↗

PubMed2001

Diffusion of phycobilisomes on the thylakoid membranes of the cyanobacterium Synechococcus 7942. Effects of phycobilisome size, temperature, and membrane lipid composition.

A variant of fluorescence recovery after photobleaching allows us to observe the diffusion of photosynthetic complexes in cyanobacterial thylakoid membranes in vivo. The unicellular cyanobacterium Synechococcus sp. PCC7942 is a wonderful model organism for fluorescence recovery after photobleaching, because it has a favorable membrane geometry and is well characterized and transformable. In Synechococcus 7942 (as in other cyanobacteria) we find that photosystem II is immobile, but phycobilisomes diffuse rapidly on the membrane surface. The diffusion coefficient is 3 x 10(-10) cm(2) s(-1) at 30 degrees C. This shows that the association of phycobilisomes with reaction centers is dynamic; there are no stable phycobilisome-reaction center complexes in vivo. We report the effects of mutations that change the phycobilisome size and membrane lipid composition. 1) In a mutant with no phycobilisome rods, the phycobilisomes remain mobile with a slightly faster diffusion coefficient. This confirms that the diffusion we observe is of intact phycobilisomes rather than detached rod elements. The faster diffusion coefficient in the mutant indicates that the rate of diffusion is partly determined by the phycobilisome size. 2) The temperature dependence of the phycobilisome diffusion coefficient indicates that the phycobilisomes have no integral membrane domain. It is likely that association with the membrane is mediated by multiple weak interactions with lipid head groups. 3) Changing the lipid composition of the thylakoid membrane has a dramatic effect on phycobilisome mobility. The results cannot be explained in terms of changes in the fluidity of the membrane; they suggest that lipids play a role in controlling phycobilisome-reaction center interaction.

Biological Transport↗

PubMed2002

A transient exchange of the photosystem II reaction center protein D1:1 with D1:2 during low temperature stress of Synechococcus sp. PCC 7942 in the light lowers the redox potential of QB.

Upon exposure to low temperature under constant light conditions, the cyanobacterium Synechococcus sp. PCC 7942 exchanges the photosystem II reaction center D1 protein form 1 (D1:1) with D1 protein form 2 (D1:2). This exchange is only transient, and after acclimation to low temperature the cells revert back to D1:1, which is the preferred form in acclimated cells (Campbell, D., Zhou, G., Gustafsson, P., Oquist, G., and Clarke, A. K. (1995) EMBO J. 14, 5457-5466). In the present work we use thermoluminescence to study charge recombination events between the acceptor and donor sides of photosystem II in relation to D1 replacement. The data indicate that in cold-stressed cells exhibiting D1:2, the redox potential of Q(B) becomes lower approaching that of Q(A). This was confirmed by examining the Synechococcus sp. PCC 7942 inactivation mutants R2S2C3 and R2K1, which possess only D1:1 or D1:2, respectively. In contrast, the recombination of Q(A)(-) with the S(2) and S(3) states did not show any change in their redox characteristics upon the shift from D1:1 to D1:2. We suggest that the change in redox properties of Q(B) results in altered charge equilibrium in favor of Q(A). This would significantly increase the probability of Q(A)(-) and P680(+) recombination. The resulting non-radiative energy dissipation within the reaction center of PSII may serve as a highly effective protective mechanism against photodamage upon excessive excitation. The proposed reaction center quenching is an important protective mechanism because antenna and zeaxanthin cycle-dependent quenching are not present in cyanobacteria. We suggest that lowering the redox potential of Q(B) by exchanging D1:1 for D1:2 imparts the increased resistance to high excitation pressure induced by exposure to either low temperature or high light.

Cyanobacteria↗

PubMed2002

Assembly of photosystem I. I. Inactivation of the rubA gene encoding a membrane-associated rubredoxin in the cyanobacterium Synechococcus sp. PCC 7002 causes a loss of photosystem I activity.

A 4.4-kb HindIII fragment, encoding an unusual rubredoxin (denoted RubA), a homolog of the Synechocystis sp. PCC 6803 gene slr2034 and Arabidopsis thaliana HCF136, and the psbEFLJ operon, was cloned from the cyanobacterium Synechococcus sp. PCC 7002. Inactivation of the slr2034 homolog produced a mutant with no detectable phenotype and wild-type photosystem (PS) II levels. Inactivation of the rubA gene of Synechococcus sp. PCC 7002 produced a mutant unable to grow photoautotrophically. RubA and PS I electron transport activity were completely absent in the mutant, although PS II activity was approximately 80% of the wild-type level. RubA contains a domain of approximately 50 amino acids with very high similarity to the rubredoxins of anaerobic bacteria and archaea, but it also contains a region of about 50 amino acids that is predicted to form a flexible hinge and a transmembrane alpha-helix at its C terminus. Overproduction of the water-soluble rubredoxin domain in Escherichia coli led to a product with the absorption and EPR spectra of typical rubredoxins. RubA was present in thylakoid but not plasma membranes of cyanobacteria and in chloroplast thylakoids isolated from spinach and Chlamydomonas reinhardtii. Fractionation studies suggest that RubA might transiently associate with PS I monomers, but no evidence for an association with PS I trimers or PS II was observed. PS I levels were significantly lower than in the wild type ( approximately 40%), but trimeric PS I complexes could be isolated from the rubA mutant. These PS I complexes completely lacked the stromal subunits PsaC, PsaD, and PsaE but contained all membrane-intrinsic subunits. The three missing proteins could be detected immunologically in whole cells, but their levels were greatly reduced, and degradation products were also detected. Our results indicate that RubA plays a specific role in the biogenesis of PS I.

Amino Acid Sequence↗

PubMed2004

Glycine 176 affects catalytic properties and stability of the Synechococcus sp. strain PCC6301 ribulose-1,5-bisphosphate carboxylase/oxygenase.

A previously described system for biological selection of randomly mutagenized ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) employing the phototrophic bacterium Rhodobacter capsulatus was used to select a catalytically altered form of a cyanobacterial (Synechococcus sp. strain PCC6301) enzyme. This mutant Rubisco, in which conserved glycine 176 was replaced with an aspartate residue, was not able to support CO(2)-dependent growth of the host strain. Site-directed mutant proteins were also constructed, e.g. asparagine and alanine residues replaced the native glycine with the result that these mutant proteins either greatly reduced the ability of R. capsulatus to support growth or had little effect, respectively. Growth phenotypes were consistent with the Rubisco activity levels associated with these proteins, and this was also borne out with purified recombinant proteins. Despite being catalytically challenged, the G176D and G176N mutant proteins were found to exhibit a more favorable interaction with CO(2) than the wild type protein but exhibited a reduced affinity for the substrate ribulose 1,5-bisphosphate. The G176A enzyme differed little from the wild type protein in these properties. None of the mutants had CO(2)/O(2) specificities that differed markedly from the wild type. Further studies taken from the known structure of the Synechococcus Rubisco indicated that substitutions at Gly-176 affected associations between large subunits. Supporting experimental data included an unusual protein concentration-dependent effect on in vitro activity, differences in thermal stability relative to the wild type protein, and aberrant migration on nondenaturing polyacrylamide gels. From these results, it is apparent that residues not directly located within the active site but near large subunit interfaces can affect key kinetic properties of Rubisco. These results suggest that further bioselection protocols (using these proteins as starting material) might yield novel mutant forms of Rubisco that relate to key functional properties.

Catalysis↗

PubMed1995

Genes encoding the group I intron-containing tRNA(Leu) and subunit L of NADH dehydrogenase from the cyanobacterium Synechococcus PCC 6301.

A part of the tRNA(Leu)(UAA) gene containing a 240-nucleotide group I intron was amplified by PCR from cyanobacterium Synechococcus PCC 6301 genomic DNA. The pre-tRNA synthesized from the cloned PCR product was efficiently self-spliced in vitro under physiological conditions. The gene encoding the tRNA(Leu)(UAA), trnL-UAA, was isolated from a Synechococcus PCC 6301 genomic library and the nucleotide sequence of a 2,167-bp portion was determined. The trnL-UAA consists of a 34-bp 5' exon, a 240-bp group I intron and a 50-bp 3' exon. In addition, three open reading frames (ORF1, ORF2 and ORF3) were found in the 5' and 3' flanking regions of trnL-UAA. The predicted protein sequence of ORF3, which is located 74-bp upstream from trnL-UAA on the opposite strand, shows 66.2% amino acid identity to that of the Synechocystis PCC 6803 gene encoding subunit L of NADH dehydrogenase (ndhL).

Amino Acid Sequence↗

PubMed1998

Nucleotide sequence of plasmid pAQ1 of marine cyanobacterium Synechococcus sp. PCC7002.

We have determined the complete nucleotide sequence of pAQ1, the smallest plasmid of the unicellular marine cyanobacterium Synechococcus sp. PCC7002. The plasmid consists of 4,809 bp and has at least four open reading frames that potentially encode polypeptides of 50 or more amino acids. We found that a palindromic element, the core sequence of which is G(G/A)CGATCGCC, is over-represented not only in plasmid pAQ1 but also in the accumulated cyanobacterial genomic sequences from Synechococcus sp. PCC6301, PCC7002, PCC7942, vulcanus and Synechocystis sp. PCC6803 within GenBank and EMBL databases. It suggests that this sequence might mediate gene rearrangement, thus increasing genetic diversity, since recombination events are frequent in cyanobacteria.

Amino Acid Sequence↗

PubMed1998

A novel plasmid recombination mechanism of the marine cyanobacterium Synechococcus sp. PCC7002.

We describe a novel mechanism of site-specific recombination in the unicellular marine cyanobacterium Synechococcus sp. PCC7002. The specific recombination sites on the smallest plasmid pAQ1 were localized by studying the properties of pAQ1-derived shuttle-vectors. We found that a palindromic element, the core sequence of which is G(G/A)CGATCGCC, functions as a resolution site for site-specific plasmid recombination. Furthermore, site-directed mutagenesis analysis of the element show that the site-specific recombination in the cyanobacterium requires sequence specificity, symmetry in the core sequence and, in part, the spacing between the elements. Interestingly, this element is over-represented not only in pAQ1 and in the genome of the cyanobacterium, but also in the accumulated cyanobacterial sequences from Synechococcus sp. PCC6301, PCC7942, vulcanus and Synechocystis sp. PCC6803 within GenBank and EMBL databases. Thus, these findings strongly suggest that the site-specific recombination mechanism based on the palindromic element should be common in these cyanobacteria.

Cyanobacteria↗

PubMed1994

The existence of eukaryotic ribonucleoprotein consensus sequence-type RNA-binding proteins in a prokaryote, Synechococcus 6301.

A group of proteins containing a conserved ribonucleoprotein consensus sequence (RNP-CS)-type RNA-binding domain (CS-RBD) of approximately 80 amino acids is present in eukaryotic cells and binds specifically to a wide variety of RNA molecules. We have isolated 12 kDa single-stranded DNA binding proteins from the unicellular cyanobacterium Synechococcus 6301. The amino-terminal sequence was determined and two distinct genomic clones were isolated from a Synechococcus 6301 genomic library. Sequence analysis revealed that two closely related proteins contain a single CS-RBD of 82 amino acids and are named as 12RNP1 and 12RNP2. Both of the CS-RBDs share the highest amino acid identity with those of chloroplast ribonucleoproteins (40-51%). The 12RNP proteins were expressed in Escherichia coli bearing plasmids encoding glutathione S-transferase/12RNP fusion proteins and subjected to in vitro nucleic acid-binding assay. Both 12RNP1 and 12RNP2 bind to RNA homopolymers poly(U) and poly(G), indicating that they might be RNA-binding proteins. This is the first example of such proteins in prokaryotes. The 12RNP1 and 12RNP2 genes are transcribed as monocistronic mRNAs and the steady-state mRNA level of 12RNP1 is over 20-fold than that of 12RNP2. Due to the easiness of genetic manipulations the cyanobacterium will provide an excellent system to analyze the function of not only cyanobacterial but also plant RNA-binding proteins.

Base Sequence↗

PubMed2000

Structure-function relationships of two closely related group IC3 intron ribozymes from Azoarcus and Synechococcus pre-tRNA.

The two group IC3 pre-tRNA introns from Azoarcus and Synechococcus share very analogous secondary structures. They are small group I ribozymes that possess only two peripheral domains, P2 and P9. However, the 3'-splice site hydrolysis activity of the Synechococcus ribozyme critically depends on P2 whereas that of Azoarcus does not, indicating that the structure-function relationships of the two ribozymes are strikingly different despite their structural resemblance. To identify the element(s) that determines the catalytic properties of these ribozymes, we undertook analyses of chimeric ribozymes prepared by swapping their structural elements. We found that the difference can be attributed to a small number of nucleotides within the conserved core region. Further analysis by employing in vitro selection revealed that a base triple interaction (P4bp3 x J6/7-2) is a critical element for determining activity and suggests the existence of a novel base quintuple involving the base triple P4bp5 x J8/7-5.

Azoarcus↗

PubMed2002

A high temperature-sensitive mutant of Synechococcus sp. PCC 7002 with modifications in the endogenous plasmid, pAQ1.

To study thermal adaptations in the cyanobacterium, Synechococcus sp. PCC 7002, we screened about 3,000 mutants for their tolerance to high temperature, and found one, SHT1, that is sensitive to high-temperature stress. The mutant had a modified gene construct in the endogenous plasmid, pAQ1. One of the four ORFs, ORF93, was duplicated, and its mRNA level was higher than in the wild type. At 38 degrees C, the growth of SHT1 was retarded as compared with the wild type, and above 38 degrees C, almost all the cells of SHT1 died. This temperature is much lower than that required for induction of heat shock proteins. Interestingly, in both the wild type and SHT1, the thermal stability of oxygen-evolving machinery increased upon acclimation to high temperatures. These findings indicate that the lack of thermal tolerance in the SHT1 strain is likely independent of the adaptation of the PSII complex and heat shock responses, whereas there are essential contributions of genes in the endogenous plasmid to the adaptation to high temperature. Thus, understanding the role of pAQ1 in the adaptation of Synechococcus sp. PCC 7002 to high-temperature environments is the first step in elucidating the function of this plasmid.

Acclimatization↗

PubMed1992

An iron stress operon involved in photosynthetic electron transport in the marine cyanobacterium Synechococcus sp. PCC 7002.

The iron-stress-induced genes isiA and isiB have been cloned and sequenced from the marine unicellular cyanobacterium Synechococcus sp. PCC 7002. These genes code for a photosystem II chlorophyll-binding protein and flavodoxin respectively. The genes form a dicistronic operon that is transcriptionally activated under iron-stress conditions to produce an abundant monocistronic message containing isiA and a much less abundant dicistronic message that also contains isiB. The arrangement of these genes, their transcriptional control and the relative abundance of the monocistronic and dicistronic messages produced under iron stress parallels the pattern shown by the freshwater cyanobacterium Synechococcus sp. PCC 7942. The genes for the corresponding proteins found under iron-replete conditions, CP-43 and ferredoxin, have also been cloned and sequenced. Northern blot analysis indicates that both of these genes are constitutively expressed under both iron-stress and iron-replete conditions.

Amino Acid Sequence↗

PubMed1997

Expression of two alternative sigma factors of Synechococcus sp. strain PCC 7002 is modulated by carbon and nitrogen stress.

The sigB and sigC genes, encoding two alternative sigma factors of the unicellular marine cyanobacterium Synechococcus sp. PCC 7002, were cloned and characterized. Strains in which the sigB and sigC genes were insertionally inactivated were viable under standard laboratory conditions, indicating that SigB and SigC are group 2 sigma factors. Starvation for either nitrogen or carbon caused an increase in sigB mRNA levels. Transcripts for the sigC gene initially increased but then decreased during nitrogen and carbon starvation. The SigC protein could not be identified in cyanobacterial extracts using antisera to Synechococcus sp. PCC 7002 SigA or RpoD from Bacillus subtilis. The ratio of the principal vegetative sigma factor, SigA, to SigB decreased during either nitrogen starvation or carbon starvation, and the levels of SigB also increased in the sigC mutant strain. These results imply that SigB and SigC play roles in modifying transcription in response to changes in carbon and nitrogen availability in this cyanobacterium.

Amino Acid Sequence↗

PubMed2001

Multiple evidence for widespread and general occurrence of type-III PHA synthases in cyanobacteria and molecular characterization of the PHA synthases from two thermophilic cyanobacteria: Chlorogloeopsis fritschii PCC 6912 and Synechococcus sp. strain MA19.

Eleven different cyanobacteria were investigated with respect to their capabilities to synthesize poly-3-hydroxybutyrate [poly(3HB)] and the type of poly-beta-hydroxyalkanoic acid (PHA) synthase accounting for the synthesis of this polyester. Several methods, including (i) Southern blot analysis using a phaC-specific DNA probe, (ii) Western blot analysis using specific polyclonal anti-PhaE antibodies raised in this study against PhaE of Synechocystis sp. strain PCC 6803, (iii) generation and sequence analysis of PCR products using phaC-specific oligonucleotides as primers, and/or (iv) cloning and sequence analysis of PHA synthase structural genes, were used to provide evidence for the presence of a type-III PHA synthase in the following cyanobacteria: Synechococcus sp. strains MA19 and PCC 6715, Chlorogloeopsis fritschii PCC 6912, Anabaena cylindrica SAG 1403-2, Cyanothece sp. strains PCC 7424, PCC 8303 and PCC 8801, and Gloeocapsa sp. strain PCC 7428. The screening was compared with corresponding studies using crude protein extracts and genomic DNA of Synechocystis sp. strain PCC 6803, as a positive control, which is so far the only cyanobacterium for which molecular data of the PHA synthase genes are available. No evidence for the presence of a type-III PHA synthase could be obtained for only three of the eleven investigated cyanobacteria (Stanieria sp. strain PCC 7437, Cyanothece sp. strain PCC 8955 and Gloeothece sp. strain PCC 6501). The entire PHA synthase structural genes of the two thermophilic cyanobacteria Synechococcus sp. strain MA19 and Chlorogloeopsis fritschii PCC 6912, and in addition a central region of the phaC gene of Cyanothece sp. strain PCC 8303, were cloned, sequenced and also heterologously expressed in Escherichia coli.

Acyltransferases↗

PubMed2002

Genotyping of axenic and non-axenic isolates of the genus Prochlorococcus and the OMF-'Synechococcus' clade by size, sequence analysis or RFLP of the Internal Transcribed Spacer of the ribosomal operon.

PCR amplicons of the Internal Transcribed Spacer (ITS) of the rrn operon of three axenic OMF (oceanic, marine and freshwater) strains of 'Synechococcus' (WH7803, PCC 7001 and PCC 6307, respectively) differ greatly in length from that of the axenic Prochlorococcus marinus subsp. pastoris PCC 9511(T), although these four cyanobacteria cluster relatively closely in phylogenetic trees inferred from 16S rRNA gene sequences. The ITSs of three strains (PCC 9511(T), PCC 6307 and PCC 7001) were sequenced and compared with those available for strains Prochlorococcus MED4 (CCMP 1378) and MIT9313 from genome sequencing projects. In spite of large differences in length, sequence and mean DNA base composition, conserved domains important for transcriptional antitermination and folding of the rRNA transcripts were identified in all ITSs. A new group-specific primer permitted ITS amplification even with non-axenic isolates of Prochlorococcus and one OMF-'Synechococcus' strain. Prochlorococcus isolates of the high-light-adapted clade (HL) differed from representatives of the low-light-adapted clade (LL) by the length of their ITS. Restriction fragment length polymorphism (RFLP) of the ITS amplicons revealed three subclusters among the HL strains. Size, sequence data and RFLP of the ITS amplicons will therefore be valuable markers for the identification of different Prochlorococcus genotypes and for their discrimination from other cyanobacterial relatives with which they often co-exist in oceanic ecosystems.

Base Sequence↗

PubMed2002

The NtcA-activated amt1 gene encodes a permease required for uptake of low concentrations of ammonium in the cyanobacterium Synechococcus sp. PCC 7942.

In the unicellular cyanobacterium Synechococcus sp. PCC 7942, ammonium/methylammonium transport activity has been characterized but ammonium transport genes have not been described. The amt1 gene encoding a permease responsible for high-affinity [14C]methylammonium transport in Synechococcus sp. PCC 7942 was cloned and inactivated. The Amt1 permease appeared essential to take up ammonium when it was present at low concentrations in the external medium and might also be involved in recapture of ammonium leaked out from the cells. Expression of amt1, which was induced in the absence of ammonium and also influenced by the inorganic carbon supply, was dependent on the NtcA transcriptional regulator. The promoter of amt1 was found to exhibit the structure of NtcA-activated promoters, and specific binding of purified NtcA to amt1 promoter sequences was observed. The results of this study indicate that amt1 belongs to the NtcA regulon and that NtcA may respond to both nitrogen and carbon availability.

Bacterial Proteins↗

PubMed1996

Fur regulates the expression of iron-stress genes in the cyanobacterium Synechococcus sp. strain PCC 7942.

A homologue of the 'ferric uptake regulation' gene (fur) was isolated from the cyanobacterium Synechococcus sp. strain PCC 7942 by an Escherichia coli-based 'in vivo repression assay'. The assay uses a reporter-gene construct containing the promoter region of the iron-regulated cyanobacterial gene isiA, fused to the coding region for chloramphenicol acetyltransferase. The isolated gene codes for a protein that has 41% sequence similarity (36% identity) to Fur from E. coli and contains the putative iron-binding motif found in the Fur proteins of purple bacteria. No significant similarity was found to the DxtR repressor that regulates the expression of toxin and siderophore production in Gram-positive bacteria. Insertional mutagenesis of the cloned cyanobacterial fur gene led to the creation of heteroallelic mutants that showed iron-deficiency symptoms in iron-replete medium, including the constitutive production of flavodoxin and of hydroxamate siderophores. Failure to eliminate wild-type copies of the fur gene from the polyploid genome of Synechococcus 7942 implies that in this cyanobacterium Fur may have essential functions in addition to the regulation of genes involved in iron scavenging or photosynthetic electron transport.

Amino Acid Sequence↗