Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PSAC”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 73 records · Page 4Linked to original sources
PubMed1987

The gene for the 9 kd polypeptide, a possible apoprotein for the iron-sulfur centers A and B of the photosystem I complex, in tobacco chloroplast DNA.

The gene for the 9 kd polypeptide (a possible apoprotein for the iron-sulfur centers A and B) of photosystem I has been located in the small single-copy region of tobacco chloroplast DNA. This gene (psaC) was identified by comparing the N-terminal amino acid sequence of the spinach 9 kd polypeptide with the entire sequence of tobacco chloroplast genome. The gene organization is ndhE (101 codons)--263 bp spacer--psaC (81 codons)--94 bp spacer--ndhD (509 codons). Northern blot hybridization revealed that psaC is transcribed in the chloroplasts. The deduced amino acid sequence and secondary structure are presented. The predicted polypeptide is rich in cysteine residues and contains a unique repeated sequence.

Amino Acid Sequence↗
PubMed1993

On the function of subunit PsaE in chloroplast Photosystem I.

Treatment of thylakoids from spinach with NaSCN removes extrinsic stroma-exposed subunits of the Photosystem I complex in addition to CF1 and some other surface proteins. By increasing the NaSCN concentration, PsaE is released first, followed by PsaD and PsaC. At 0.5 M NaSCN, about 80% of PsaE is resolved without significant loss of other PS I polypeptides. Time-resolved fluorescence spectroscopy showed no significant alteration of PS I isolated from membranes thus treated with regard to energy transfer within the antennas as well as primary charge separation. Washing of thylakoids with NaSCN results in inhibition of electron transport from an artificial electron donor (ascorbate/DAD) to either methylviologen or NADP. Although higher NaSCN concentrations are required for inhibition than for resolution of PsaE, electron transport is restored by reconstitution with isolated PsaE from Synechococcus. We conclude that inhibition is due to dislocation of PsaC as a consequence of PsaE resolution, impeding efficient electron transfer from Fx to FA/FB. An antibody raised against PsaC inhibits methylviologen reduction only when PsaE has been removed previously. An antibody raised against PsaE inhibits electron transport to NADP, but not to methylviologen. We conclude that binding of this antibody sterically hinders the access of ferredoxin either to the FA/FB center or the catalytic site of ferredoxin:NADP oxidoreductase (FNR). Our results suggest an essential role of PsaE in stabilization of the acceptor side of PS I, in particular in maintenance of the functional integrity between the FA/FB protein and the membrane-integral sector of the PS I core.

Amino Acid Sequence↗
PubMed1998

Penicillin tolerance genes of Streptococcus pneumoniae: the ABC-type manganese permease complex Psa.

Downregulation of the major autolysin in Streptococcus pneumoniae leads to penicillin tolerance, a feature that is characterized by the ability to survive but not grow in the presence of antibiotic. Screening a library of mutants in pneumococcal surface proteins for the ability to survive 10x minimum inhibitory concentration (MIC) of penicillin revealed over 10 candidate tolerance genes. One such mutant contained an insertion in the known gene psaA, which is part of the psa locus. This locus encodes an ABC-type Mn permease complex. Sequence analysis of adjacent DNA extended the known genetic organization of the locus to include two new open reading frames (ORFs), psaB, which encodes an ATP-binding protein, and psaC, which encodes a hydrophobic transmembrane protein. Mutagenesis of psaB, psaC, psaA and downstream psaD resulted in penicillin tolerance. Defective adhesion and reduced transformation efficiency, as reported previously for a psaA- mutant, were phenotypes shared by psaB-, psaC- and psaD- knockout mutants. Western blot analysis demonstrated that the set of mutants expressed RecA, but none of them showed translation of the autolysin gene, which is located downstream of recA. The addition of manganese (Mn) failed to correct the abnormal physiology. These results suggest that this ABC-type Mn permease complex has a pleiotropic effect on pneumococcal physiology including adherence and autolysis. These are the first genes suggested as being involved in triggering autolysin. The results raise the possibility that loss of function of PsaA, by vaccine-induced antibody for instance, may promote penicillin tolerance.

ATP-Binding Cassette Transporters↗
PubMed1996

Mutational analysis of photosystem I polypeptides. Role of PsaD and the lysyl 106 residue in the reductase activity of the photosystem I.

The ADC4 mutant of the cyanobacterium Synechocystis sp. PCC 6803 was studied to determine the structural and functional consequences of the absence of PsaD in photosystem I. Isolated ADC4 membranes were shown to be deficient in ferredoxin-mediated NADP(+) reduction, even though charge separation between P700 and FA/FB occurred with high efficiency. Unlike the wild type, FB became preferentially photoreduced when ADC4 membranes were illuminated at 15 K, and the EPR line shapes were relatively broad. Membrane fragments oriented in two dimensions on thin mylar films showed that the g tensor axes of FA- and FB- were identical in the ADC4 and wild type strains, implying that PsaC is oriented similarly on the reaction center. PsaC and the FA/FB iron-sulfur clusters are lost more readily from the ADC4 membranes after treatment with Triton X-100 or chaotropic agents, implying a stabilizing role for PsaD. The specific role of Lys106 of PsaD, which can be crosslinked to Glu93 of ferredoxin (Lelong et al. (1994) J. Biol. Chem. 269, 10034-10039), was probed by site-directed mutagenesis. Chemical cross-linking and protease treatment experiments did not reveal any drastic alterations in the conformation of the mutant PsaD proteins. The EPR spectra of FA and FB in membranes of the Lys106 mutants were similar to those of the wild type. Membranes of all Lys106 mutants showed wild type rates of flavodoxin reduction and flavodoxin-mediated NADP+ reduction, but had 10-54% decrease in the ferredoxin-mediated NADP+ reduction rates. This implies that Lys106 is a dispensable component of the docking site on the reducing side of photosystem I and an ionic interaction between Lys106 of PsaD and Glu93 of ferredoxin is not essential for electron transfer to ferredoxin. These results demonstrate that PsaD serves distinct roles in modulating the EPR spectral characteristics of FA and FB, in stabilizing PsaC on the reaction center, and in facilitating ferredoxin-mediated NADP+ photoreduction on the reducing side of photosystem I.

Base Sequence↗
PubMed1997

Both RNA editing and RNA cleavage are required for translation of tobacco chloroplast ndhD mRNA: a possible regulatory mechanism for the expression of a chloroplast operon consisting of functionally unrelated genes.

Tobacco chloroplast genes encoding a photosystem I component (psaC) and a NADH dehydrogenase subunit (ndhD) are transcribed as a dicistronic pre-mRNA which is then cleaved into short mRNAs. An RNA protection assay revealed that the cleavage occurs at multiple sites in the intercistronic region. There are two possible initiation codons in the tobacco ndhD mRNA: the upstream AUG and the AUG created by RNA editing from the in-frame ACG located 25 nt downstream. Using the chloroplast in vitro translation system, we found that translation begins only from the edited AUG. The extent of ACG to AUG editing is partial and depends on developmental and environmental conditions. In addition, the in vitro assay showed that the psaC/ndhD dicistronic mRNA is not functional and that the intercistronic cleavage is a prerequisite for both ndhD and psaC translation. Using a series of mutant mRNAs, we showed that an intramolecular interaction between an 8 nt sequence in the psaC coding region and its complementary 8 nt sequence in the 5' ndhD UTR is the negative element for translation of the dicistronic mRNA. A possible mechanism in which the differential expression of the chloroplast operon consists of functionally unrelated genes is discussed.

Chloroplasts↗
PubMed2002

In vivo characterization of the psa genes from Streptococcus pneumoniae in multiple models of infection.

Differential fluorescence induction technology was used to identify promoters of Streptococcus pneumoniae genes that are expressed during lung infection of the mouse. Among the promoter clones that were identified multiple times was the psa promoter, which drives expression of the psaBCA operon. These genes have been identified previously and shown to encode a manganese permease system as well as play a role in the virulence of this organism. Mutations in psaB, psaC or psaA result in growth limitation in low manganese. The expression of the psa operon was examined in vivo and the virulence of deletion mutants of psaB, psaC, psaA and psaBCA was assessed in four different animal models of infection. The psa promoter was induced more than ten-fold in vivo using an intraperitoneal chamber implant model. The psaB, psaC and psaA mutants were completely attenuated in systemic, respiratory tract and otitis media infections. In addition, these mutants were unable to grow in an implanted peritoneal chamber, but growth was restored by the addition of manganese to the chambers.

ATP-Binding Cassette Transporters↗
PubMed1999

Characterization of two photosynthetic mutants of maize

We describe here the biochemical characteristics of the hcf44 and hcf47 (high chlorophyll fluorescence) mutants of maize (Zea mays L.). Both mutants were sensitive to high light intensities, exhibiting reduced growth and fluorescence intensity. Electron transport through the mutants' photosystem (PS) I and PSII reaction centers was reduced and NADP(+) photoreduction was absent. Western analysis revealed that the hcf44 mutant was missing some or all of the PsaC, PsaD, and PsaE polypeptides of the PSI reaction center, and reverse transcriptase-polymerase chain reaction demonstrated that this loss was the result of a posttranscriptional event. The hcf47 mutant had reduced levels of many PSI and PSII polypeptides. These data indicate a possible defect in the synthesis or assembly of the PsaC subunit in the hcf44 mutant, whereas the hcf47 mutant may have a more general defect in the biogenesis of photosynthetic membranes. Our results demonstrate the coordinated assembly of the peripheral proteins into the PSI complexes of higher plants and demonstrate the in vivo requirement of PsaC, PsaD, and PsaE subunits for the function of PSI in higher plants.

Journal Article↗
PubMed1989

[A new transluminal angioplasty for the treatment of arteriosclerosis obliterans].

A Peripheral Simpson Atherectomy Catheter (PSAC), which permits transluminal excision and removal of diseased intima, has been tested experimentally and clinically. The device consists of a tubular housing and a cutting mechanism to excise the intima protruding into the housing. Experimentally, vascular clay model was used to estimate its efficacy. Multiple passages improved lumen size and inner smoothness, and there was some difficulty to treat curved models. Clinically, 9 lesions in 7 patients of iliofemoral atheromatous disease were treated with PSAC. Recanalization was achieved successfully except for two lesions, one a soft atheroma and the other a curved vessel. No angiographic dissections or acute arterial occlusions occurred. Despite the procedure was complicated, it seemed safe and effective. In order to improve this method, an angioplastic catheter which had a laser probe in its housing was newly designed. Nd-YAG laser was irradiated with this catheter to the atherosclerotic lesions which were induced by a high cholesterol diet in rabbit. It left smoother surface and less thermal injury than usual irradiation with contact laser probe, but it needed more energy. These results showed that PSAC can be an alternative transluminal angioplasty and the new designed laser catheter is useful, but more experiments are required to establish these procedures.

Adult↗
PubMed1987

Identification of a chloroplast-encoded 9-kDa polypeptide as a 2[4Fe-4S] protein carrying centers A and B of photosystem I.

An improved procedure is reported for large-scale preparation of photosystem I (PS-I) vesicles from thylakoid membranes of barley (Hordeum vulgare L.). The PS-I vesicles contain polypeptides of molecular masses 82, 18, 16, 14, and 9 kDa in an apparent molar ratio of 4:2:2:1:2. The 18-, 16-, and 9-kDa polypeptides were purified to homogeneity after exposure of the PS-I vesicles to chaotropic agents. The isolated 9-kDa polypeptide binds 65-70% of the zero-valence sulfur of denatured PS-I vesicles, and the remaining 30-35% is bound to P700-chlorophyll a-protein 1. The N-terminal amino acid sequence (29 residues) of the 9-kDa polypeptide was determined. Comparison with the nucleotide sequence of the chloroplast genome of Marchantia polymorpha (Ohyama, K., Fukuzawa, H., Kohchi, T., Shirai, H., Sano, T., Sano, S., Umesono, K., Shiki, Y., Takeuchi, M., Chang, Z., Aota, S.-i., Inokuchi, H., and Ozeki, H. (1986) Nature 322, 572-574) and of Nicotiana tabacum (Shinozaki, K., Ohme, M., Tanaka, M., Wakasugi, T., Hayashida, N., Matsubayashi, T., Zaita, W., Chunwongse, J., Obokata, J., Yamaguchi-Shinozaki, K., Ohto, C., Torazawa, K., Meng, B. Y., Sugita, M., Deno, H., Kamogashira, T., Yamada, K., Kusuda, J., Takaiwa, F., Kato, A., Tohdoh, N., Shimada, H., and Sugiura, M. (1986) EMBO J. 5, 2043-2049) identified the chloroplast gene encoding the 9-kDa polypeptide. We designate this gene psaC. The complete amino acid sequence deduced from the psaC gene identifies the 9-kDa PS-I polypeptide as a 2[4Fe-4S] protein. Since P700-chlorophyll a-protein 1 carries center X, the 9-kDa polypeptide carries centers A and B. A hydropathy plot permits specific identification of the cysteine residues which coordinate centers A and B, respectively. Except for the loss of the N-terminal methionine residue, the primary translation product of the psaC gene is not proteolytically processed. P700-chlorophyll a-protein 1 binds 4 iron atoms and 4 molecules of acid-labile sulfide/molecule of P700. Each of the two apoproteins of P700-chlorophyll a-protein 1 contains the sequence Phe-Pro-Cys-Asp-Gly-Pro-Gly-Arg-Gly-Gly-Thr-Cys (Fish, L. E., Kück, U., and Bogorad, L. (1985) J. Biol. Chem. 260, 1413-1421). The stoichiometry of the component polypeptides of PS-I indicates the presence of four copies of this sequence per molecule of P700. Center X may be composed of two [2Fe-2S] centers bound to the 8 cysteine residues contained in these four segments.

Amino Acid Sequence↗
PubMed1993

Isolation and structural characterization of monomeric and trimeric photosystem I complexes (P700.FA/FB and P700.FX) from the cyanobacterium Synechocystis PCC 6803.

An isolation procedure was developed for the cyanobacterium Synechocystis 6803 (and 6714) which yields both monomeric and trimeric photosystem I complexes (P700.FA/FB complexes) depleted of the stroma-exposed subunits PsaC, -D, and -E (P700.FX complexes). Analysis by high resolution gel electrophoresis in combination with immunoblotting and N-terminal sequencing reveals the selective and quantitative removal of PsaC, -D, and -E from the P700.FA/FB complex, containing PsaA, -B, -C, -D, -E, -F, -K, -L and at least two subunits < or = 4 kDa. Monomeric and trimeric P700.FX complexes show an identical subunit composition and an identical charge recombination half-time of 750 +/- 250 microseconds as determined by flash-induced absorption change measurements, reflecting the quantitative loss of iron-sulfur clusters FA/FB and the presence of cluster FX. The existence of a stable trimeric P700.FX complex enables a detailed structural analysis by electron microscopy with high resolution. Comparison of averaged top and side view projections of P700.FX and P700.FA/FB complexes show that the height of the complex is reduced by about 2.5-3.3 nm upon removal of the three stroma-exposed subunits and indicate the position of these three subunits on the PS I surface. While the outer contours of the stroma exposed mass of PS I agree very well with the three-dimensional crystal analysis recently published for trimeric PS I of Synechococcus elongatus (Krauss, N., Hinrichs, W., Witt, I., Fromme, P., Pritzkow, W., Dauter, Z., Betzel, C., Wilson, K. S., Witt, H. T., and Saenger, W. (1993) Nature 361, 326-330), only the structural analysis presented here is able to assign the stroma-exposed mass exclusively to the subunits PsaC, -D, and -E and to exclude a contribution of other subunits.

Amino Acid Sequence↗
PubMed1992

Nucleotide sequence and expression of the gene for the 9 kDa FA/FB component of photosystem I from the cyanobacterium Anabaena sp. PCC7120.

The nucleotide sequence of an 813 bp Ssp I-Hinc II fragment containing the psaC gene from Anabaena sp. PCC 7120 is reported. The gene encodes a polypeptide of 81 amino acids, has a single transcript of size approximately 480 nucleotides and a single startpoint of transcription. It is flanked by a ribosome binding site on the 5' end and a potential transcription terminator on the 3' end. Comparison of the amino acid sequences of the psaC gene product from sixteen organisms shows that cyanobacteria group as a cluster distinct from monocotyledonous and dicotyledonous plants and that individual amino acids are diagnostic of each cluster.

Amino Acid Sequence↗
PubMed1992

Cloning and transcription analysis of the ndh(A-I-G-E) gene cluster and the ndhD gene of the cyanobacterium Synechocystis sp. PCC6803.

The plastid DNA of higher plants contains eleven reading frames that are homologous to subunits of the mitochondrial NADH-ubiquinone oxidoreductase (complex I). The genes are expressed, but a plastid NAD(P)H dehydrogenase has not yet been isolated and the function of the enzyme in plastid metabolism is unknown. Cyanobacteria also contain a NADH dehydrogenase that is homologous to the mitochondrial complex I. The enzyme is sensitive to rotenone and is located on the cytoplasmic and the thylakoid membrane. We report here the sequence of five subunits (ndhA, -I, G, -E and -D) of the NADH dehydrogenase from the unicellular cyanobacterium Synechocystis sp. PCC6803. As in plastid DNA, the genes ndh(A-I-G-E) are clustered and probably constitute an operon. The ndhD gene is associated with a gene encoding an iron-sulphur protein of photosystem I (psaC) as in plastid DNA. In contrast to the situation in plastids, psaC and ndhD are not cotranscribed but transcribed from opposite strands. The deduced amino acid sequence of the cyanobacterial polypeptides is more similar to the corresponding plastid (40-68% identity) than to the corresponding mitochondrial subunits (17-39% identity). Thus, the cyanobacterial NADH-dehydrogenase provides a prokaryotic model system which is more suitable to genetic analysis than the enzyme of plastids.

Amino Acid Sequence↗
PubMed1989

Nucleotide sequences of cDNA clones encoding the entire precursor polypeptide for subunit VI and of the plastome-encoded gene for subunit VII of the photosystem I reaction center from spinach.

Recombinant phage which encode the entire precursor polypeptide for subunit VI of the photosystem I reaction center have been selected from a lambda gt11 cDNA expression library made from polyadenylated RNA of spinach seedlings. The sequence predicts a precursor polypeptide of 144 amino acids (Mr = 15.3 kDa), a mature protein of 95 residues (Mr = 10.4 kDa) that lacks methionine, histidine and cysteine, and a transit peptide of 49 residues (Mr = 4.9 kDa). The corresponding gene(s) is (are) designated psaH. The gene for subunit VII, psaC, has been located in the small single-copy region of the spinach plastid chromosome using a synthetic oligonucleotide and a heterologous hybridization probe. It is part of a polycistronic transcription unit that is constitutively expressed and processed. Putative processing products include a monocistronic RNA for psaC. The polypeptide chain of 18 (deduced) amino acids is highly conserved and strikingly resembles bacterial-type ferredoxins. It harbours cysteine residues that appear to be involved in the ligation of the two 4Fe4S centres A and B in photosystem I. None of the two subunits appears to be membrane-spanning, and subunit VI, as subunit VII, is located at the reducing (stromal) side of the reaction center. All available information on the major subunits of photosystem I from spinach has been combined into a (revised) topographic model. Evidence that the innermost - plastome-encoded - core of photosystem I represents an old bacterial heritage in present day chloroplasts is discussed.

Amino Acid Sequence↗
PubMed2005

Dynamics of fluxes through photosynthetic complexes in response to changing light and inorganic carbon acclimation in Synechococcus elongatus.

Cyanobacteria acclimate to environmental inorganic carbon (C(i)) concentrations through re-organisations of photosynthetic function and the induction of carbon concentrating mechanisms (CCMs), which alter and constrain their subsequent acclimation to changing light. We grew cells acclimated to high C(i) (4 mM) or low C(i) (0.02 mM), shifted them from 50 micromol m(-2) s(-1) to 500 micromol m(-2) s(-1), and quantified their photosynthetic performance in parallel with quantitation of allocations to key indicator macromolecules. Pigments cell(-1) declined, PsbA (PS II), AtpB (ATP Synthase), RbcL (Rubisco) and GlnA (Glutamine Synthetase) increased, and PsaC (PS I) remained stable through the light shift. The increase in these protein pools was slower and smaller in low C(i) cells, but acted in both cell types to re-normalise the electron fluxes through the catalytic complexes back toward values before the light shift (for PsbA and GlnA) or even below the initial flux per complex (for RbcL). In contrast, an increased electron flux per PsaC was sustained for at least 6 h after the increase in light. Initially, high levels of PS II cell(-1) and PS II connectivity in high C(i) cells caused a more rapid net photoinactivation of PS II in high C(i) cells than in low C(i) cells, depressing the rate of PS II-specific electron transport (PS II ETR) to levels similar to linear ETR (net O(2) evolution minus respiration). In low C(i) cells, PS II ETR remained in excess of linear ETR and may have helped maintain CCM activity. The pool sizes of PsbA, AtpB and GlnA correlated with cellular growth rate, and changed at similar rates in high C(i) and low C(i) cells when expressed on a generational rather than chronological timescale, which has implications for differing ecology of high and low C(i) cells under variable natural light.

Acclimatization↗
PubMed1993

Small subunits of Photosystem I reaction center complexes from Synechococcus elongatus. II. The psaE gene product has a role to promote interaction between the terminal electron acceptor and ferredoxin.

Function of a subunit polypeptide (the psaE gene product) of Photosystem I (PS I) reaction center complexes was investigated by comparing the reactivity of the reduced iron-sulfur centers (FA/FB)- with ferredoxin among Synechococcus PS I complexes which had been variously depleted of this polypeptide. Ferredoxin at or below 1 microM can accept electrons from (FA/FB)- effectively competing with the back reaction between P-700+ and (FA/FB)- in the thylakoid membranes and PS I complexes that contained all the eight small subunits. The high reactivity of (FA/FB)- with low concentrations of ferredoxin was observed in PS I complexes which contain only the products of psaC, psaD and psaE genes but not in complexes which carry the psaC, psaD, psaL and psaK gene products but no psaE gene product. Varied amounts of the psaE gene product were extracted by treatment with different concentrations of a cationic detergent, dodecyltrimethylammonium bromide, and 2.5 M NaCl. The solubilized polypeptide was then reconstituted to the depleted complexes. The magnitudes of the back reaction that could be suppressed by addition of ferredoxin at or below 1 microM were well correlated to the amounts of the psaE polypeptide remained bound or rebound to the complexes. It is concluded that the product of the psaE gene has a role to promote the interaction between the terminal bound electron acceptor and ferredoxin. A high autooxidizability of (FA/FB)- and contrasting effects of lipophilic cations and anions on the rate of the back reaction from (FA/FB)- to P-700+ were also reported.

Cetrimonium↗
PubMed2005

Characterization of the 5'- and 3'-ends of mRNAs of ndhH, ndhA and ndhI genes of the plastid ndhH-D operon.

The monocistronic mRNAs of ndhH and ndhA genes of the plastid ndhH-D operon accumulate during senescence. In a step forward to discover the mechanisms involved in the production of mature transcripts of the ndhH-D operon, we determined the 5 - and 3 -ends of low-molecular-weight ndhH, ndhA and ndhI transcripts of barley. The 3'-end of the only ndhH mRNA detected (1622 b) extends 421 b into exon1 of ndhA. Several monocistronic ndhA mRNAs were identified and most of them extend their 3'-ends through the adjacent intergenic 101 b region to around 105 b into ndhI, the neighboring gene in the operon. Unspliced ndhA transcripts (around 2.4 kb and intron-containing) were also identified with different 3'-ends extending almost 200 b into ndhI. In contrast, all ndhA transcripts showed the same 5'-end 65 b upstream of the ndhH stop codon. 5'-ends of all ndhA and ndhH transcripts seem produced by nuclease cleavages between the last AA of the consensus sequence AAUGAA present 66 and 16 b upstream of the respective start codon. Secondary structure predictions suggest that 3'-end extensions provide 3'-UTR stabilizing elements to ndhH-D transcripts. Therefore, the processing of the 7.8 kb primary transcript frequently involves intra-genic cleavages sacrificing downstream gene messages and decreasing the efficiency of the conversion to mature ndh mRNAs. Significantly, the maturation of ndhE mRNA would not sacrifice the downstream psaC message, contributing to higher levels of psaC mRNA than of ndh mRNAs.

3' Untranslated Regions↗
PubMed2004

Construction and use of GFP reporter vectors for analysis of cell-type-specific gene expression in Nostoc punctiforme.

Two transcriptional reporter shuttle vectors were constructed for the filamentous cyanobacterium Nostoc punctiforme using the green fluorescence protein (GFP) reporter. Both the ampicillin- and kanamycin-resistant versions of the plasmid allow promoters to be directionally cloned into a multiple cloning site preceding a promoterless gfp gene using an Escherichia coli host. The ability of the self-replicating shuttle plasmids to report cell-type-specific gene expression in N. punctiforme was tested by cloning promoters expressed in normal vegetative cells, nitrogen-fixing heterocysts and spore-like akinetes. A P(psaC) reporter gene fusion was expressed in vegetative cells and not in heterocysts, whereas GFP driven from P(hetR) was found highly expressed in heterocysts. GFP expression driven by the promoter for the N. punctiforme homologue of the akinete-specific gene avaK was expressed in developing akinetes. Decreased expression of GFP from the P(psaC) reporter in hormogonia was also observed. The results demonstrate the utility of these GFP vectors to study cell-type-specific gene expression in differentiating filamentous cyanobacteria.

Cyanobacteria↗
PubMed2001

Iron-sulfur clusters in type I reaction centers.

Type I reaction centers (RCs) are multisubunit chlorophyll-protein complexes that function in photosynthetic organisms to convert photons to Gibbs free energy. The unique feature of Type I RCs is the presence of iron-sulfur clusters as electron transfer cofactors. Photosystem I (PS I) of oxygenic phototrophs is the best-studied Type I RC. It is comprised of an interpolypeptide [4Fe-4S] cluster, F(X), that bridges the PsaA and PsaB subunits, and two terminal [4Fe-4S] clusters, F(A) and F(B), that are bound to the PsaC subunit. In this review, we provide an update on the structure and function of the bound iron-sulfur clusters in Type I RCs. The first new development in this area is the identification of F(A) as the cluster proximal to F(X) and the resolution of the electron transfer sequence as F(X)-->F(A)-->F(B)-->soluble ferredoxin. The second new development is the determination of the three-dimensional NMR solution structure of unbound PsaC and localization of the equal- and mixed-valence pairs in F(A)(-) and F(B)(-). We provide a survey of the EPR properties and spectra of the iron-sulfur clusters in Type I RCs of cyanobacteria, green sulfur bacteria, and heliobacteria, and we summarize new information about the kinetics of back-reactions involving the iron-sulfur clusters.

Chlorobi↗