Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Photosystem I functions as a light-driven plastocyanin-ferredoxin oxidoreductase in the photosynthetic membranes of cyanobacteria and chloroplasts. A mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 that contains a deletion of the psaF gene and a transcriptionally inactive psaJ gene has assembled photosystem I complexes that lack PsaF, a lumenal protein and PsaJ, a 4-kDa hydrophobic protein. The cells of the mutant and wild type strains have similar rates of photosynthetic electron transfer and P700+ rereduction under linear and cyclic electron transfer conditions. Analysis of flash-induced absorption transients at 700 nm demonstrate that the absence of PsaF in purified mutant photosystem I did not affect the rate of P700 rereduction by cytochrome c553. Therefore, PsaF is not essential for docking of cytochrome c553. We also studied the organization of the proteins of mutant and wild type photosystem I by comparing their accessibility to digestion by thermolysin or to removal by 1 M NaI. The PsaA-PsaB subunits were more easily degraded by thermolysin in the mutant photosystem I. Thermolysin cleavage of PsaB yielded two major fragments that were immunoreactive with an antibody raised against the C terminus of PsaB. The N termini of these PsaB peptides mapped at Ile482 and Ile498 residues, thus identifying a surface-exposed domain of the core of photosystem I. The PsaE subunit could be removed by 1 M NaI and was rapidly digested by thermolysin in the mutant but not in the wild type photosystem I. Therefore, PsaF and PsaJ subunits of photosystem I have dispensable accessory roles in the function and organization of the complex.
 ...
PMID:Function and organization of photosystem I in a cyanobacterial mutant strain that lacks PsaF and PsaJ subunits. 810 55

Under conditions of iron deprivation cyanobacteria produce flavodoxin to replace ferredoxin as the terminal electron acceptor of photosynthesis. In unicellular cyanobacteria, the gene for flavodoxin is the second open reading frame in a dicistronic operon whose transcription is tightly regulated by iron. The first gene, isiA, produces a protein that is very similar to CP43, a chlorophyll-binding, antenna protein of the photosystem II reaction center. In the filamentous, heterocystous cyanobacterium Anabaena sp. PCC 7120, isiA and the gene for flavodoxin are located in separate operons with independent promoters. In this paper, we report on the sequence of isiA and show that it is found in a monocistronic operon that is transcriptionally regulated to be expressed under iron stress but does not produce detectable transcripts under conditions of iron repletion. We also report on the sequence, organization and expression of the gene that codes for CP43, psbC. In Anabaena sp. PCC 7120, psbC has a genetic organization similar to that of other cyanobacteria and higher plants; the 5' end of psbC overlaps the 3' end of psbDI. Transcriptional analysis of the psbDC operon showed that it is constitutively expressed in both iron-repleted and iron-stressed conditions; however, a new monocistronic transcript was detected that contains psbC and is preferentially expressed under iron stress conditions.
 ...
PMID:Photosystem II genes isiA, psbDI and psbC in Anabaena sp. PCC 7120: cloning, sequencing and the transcriptional regulation in iron-stressed and iron-repleted cells. 811 Oct 27

Ferredoxin isolated from the cyanobacterium Synechocystis sp. PCC 6803 has been chemically cross-linked to purified photosystem I from the same organism. The reaction was catalyzed by N-ethyl-3-(3-dimethylaminopropyl)carbodiimide in the presence of N-hydroxysulfosuccinimide. A short reaction time and neutral pH values can be used in the presence of the two reagents, ensuring the integrity of both of the proteins and the iron-sulfur cluster of the ferredoxin. The only covalent complex detected comprised ferredoxin and the photo-system I (PSI)-D subunit, as identified by antibodies probing after electrophoresis. Electron paramagnetic resonance measurements of this covalent complex have shown that the cross-linked ferredoxin was entirely photoreducible by photosystem I and that the molar ratio of ferredoxin to PSI was close to 1. Extensive sequencing of the peptides obtained after proteolysis of the purified cross-linked product led to the identification of a covalent bond between glutamic acid 93 of ferredoxin and lysine 106 of the PSI-D subunit.
 ...
PMID:Identification of the amino acids involved in the functional interaction between photosystem I and ferredoxin from Synechocystis sp. PCC 6803 by chemical cross-linking. 814 1

The gene for the low potential cytochrome c (petK) was isolated from a genomic library of Synechocystis PCC 6803. The nucleotide sequence of this gene contains two regions with sequence similarity to two regions in the gene for the high potential cytochrome c6 of the organism. The sixth iron ligand can be identified with a conserved histidine. Experiments demonstrate the reduction of the low potential cytochrome by reduced ferredoxin II. The heme of the cytochrome is flanked by lysines which may be involved in orienting the ferredoxin near the site of electron donation.
 ...
PMID:Cloning and sequence analysis of the gene encoding the low potential cytochrome c of Synechocystis PCC 6803. 818 63

A 329 bp DNA segment from both Anabaena variabilis and Anabaena PCC 7119 was amplified using the polymerase chain reaction (PCR). The sequences from the two cyanobacteria showed strong similarities to the corresponding part of the nifJ gene from Klebsiella pneumoniae and Enterobacter agglomerans. The present findings underline earlier results of enzymatic studies that heterocystous cyanobacteria possess a pyruvate:ferredoxin (flavodoxin) oxidoreductase (PFO). The nifJ gene segment could not be detected in the non-dinitrogen-fixing, unicellular cyanobacterium Anacystis nidulans which is also in accord with previous findings from enzyme assays.
 ...
PMID:Identification of the nifJ gene coding for pyruvate: ferredoxin oxidoreductase in dinitrogen-fixing cyanobacteria. 835 52

Of the stroma-accessible proteins of photosystem I (PSI) from Synechocystis sp. PCC 6803, the PSI-C, PSI-D and PSI-E subunits have already been characterized, and the corresponding genes isolated. PCR amplification and cassette mutagenesis were used in this work to delete the psaE gene. PSI particles were isolated from this mutant, which lacks subunit PSI-E, and the direct photoreduction of ferredoxin was investigated by flash absorption spectroscopy. The second order rate constant for reduction of ferredoxin by wild type PSI was estimated to be approximately 10(9) M-1s-1. Relative to the wild type, PSI lacking PSI-E exhibited a rate of ferredoxin reduction decreased by a factor of at least 25. After reassociation of the purified PSI-E polypeptide, the original rate of electron transfer was recovered. When a similar reconstitution was performed with a PSI-E polypeptide from spinach, an intermediate rate of reduction was observed. Membrane labeling of the native PSI with fluorescein isothiocyanate allowed the isolation of a fluorescent PSI-E subunit. Peptide analysis showed that some residues following the N-terminal sequence were labeled and thus probably accessible to the stroma, whereas both N- and C-terminal ends were probably buried in the photosystem I complex. Site-directed mutagenesis based on these observations confirmed that important changes in either of the two terminal sequences of the polypeptide impaired its correct integration in PSI, leading to phenotypes identical to the deleted mutant. Less drastic modifications in the predicted stroma exposed sequences did not impair PSI-E integration, and the ferredoxin photoreduction was not significantly affected. All these results lead us to propose a structural role for PSI-E in the correct organization of the site involved in ferredoxin photoreduction.
 ...
PMID:Evidence for the involvement of PSI-E subunit in the reduction of ferredoxin by photosystem I. 838 13

We have previously reported that the ferredoxin I gene from Synechococcus sp. PCC 7942 is regulated by iron at the level of differential mRNA stability. To identify iron-responsive elements in the Synechococcus ferredoxin transcript, we have tested chimaeric constructs containing translational fusions between the Synechococcus and the Anabaena sp. PCC 7937 ferredoxin genes for iron-dependent expression in transgenic Synechococcus strains. This strategy was based on the observation that the level of the Anabaena ferredoxin mRNA did not increase upon iron addition in Synechococcus. Our results show that the presence of the first 207 nucleotides of the Synechococcus ferredoxin transcript is sufficient to confer iron responsiveness to the chimaeric transcripts. This iron responsiveness was accomplished by an increased stability of the chimaeric transcript in the presence of iron, as was found for the intact Synechococcus ferredoxin gene. Addition of the translation inhibitor chloramphenicol to the cultures led to a rapid stabilization, in low- and high-iron conditions, of the wild-type Synechococcus ferredoxin transcript as well as all chimaeric ferredoxin transcripts tested. These results suggest the existence of a constitutively expressed nuclease capable of degrading the ferredoxin transcripts. They further support the suggestion that the first 207 nucleotides of the Synechococcus transcript contain a specific sequence that is recognized by an iron-responsive factor and that this interaction leads to protection against degradation.
 ...
PMID:Iron-dependent protection of the Synechococcus ferredoxin I transcript against nucleolytic degradation requires cis-regulatory sequences in the 5' part of the messenger RNA. 840 Jan 25

The effect of iron on ferredoxin I specific mRNA levels was studied in the cyanobacterial strains Synechococcus sp. PCC 7942 (Anacystis nidulans R2) and Anabaena sp. PCC 7937 (Anabaena variabilis ATCC 29413). In both strains addition of iron to iron-limited cells resulted in a rapid increase in ferredoxin mRNA levels. To investigate the possible role of the ferredoxin promoter in iron regulation, a vector for promoter analysis in Synechococcus PCC 7942 strain R2-PIM9 was constructed, which contains the ferredoxin promoter fused to the gene encoding beta-glucuronidase (GUS) as reporter. Neither the Synechococcus nor the Anabaena ferredoxin promoter was able to direct iron-regulated GUS activity in Synechococcus R2-PIM9, indicating that transcription initiation is not responsible for the iron-dependent ferredoxin mRNA levels. Determination of the half-life of the ferredoxin transcript in iron-supplemented and iron-limited cells revealed that, in both strains, the ferredoxin transcript is much more stable in iron-supplemented cells than in iron-limited cells. These results lead to the conclusion that in these strains, iron-regulated expression of the ferredoxin I gene is mediated via differential mRNA stability.
 ...
PMID:Iron-dependent stability of the ferredoxin I transcripts from the cyanobacterial strains Synechococcus species PCC 7942 and Anabaena species PCC 7937. 845 69

Isolation of cyanobacterial ferredoxin is normally carried out using nucleases in order to degrade the nucleic acids that accompany this protein during the purification procedure. However, this practice presents the inconvenience that these proteins remain in trace amounts in the purified ferredoxin preparations, although they are not visible by electrophoretical techniques. Evidence of that fact is shown in this report and an alternative procedure is described for the rapid preparation of ferredoxin from crude extracts of Anabaena PCC 7119. The method involves a treatment of the crude extract with streptomycin sulphate, a high molecular weight polication that precipitates the nucleic acids in the beginning of the purification.
 ...
PMID:Interference of nucleases in cyanobacterium ferredoxin purification. 853 39

The narB gene from the cyanobacterium Synechococcus sp. PCC 7942 was cloned downstream from the LacI-regulated promoter Ptrc in the Escherichia coli vector pTrc99A, rendering plasmid pCSLM1. Addition of isopropyl-beta-D-thiogalactoside to E. coli (pCSLM1) resulted in the parallel expression of a 76 kDa polypeptide and a nitrate reductase activity with properties identical to those known for nitrate reductase isolated from Synechococcus cells. As is the case for nitrate reductase from Synechococcus cells, either reduced methyl viologen or reduced ferredoxin could be used as an electron donor for the reduction of nitrate catalyzed by E. coli (pCSLM1) extracts. This data shows that narB is a cyanobacterial structural gene for nitrate reductase.
 ...
PMID:A cyanobacterial narB gene encodes a ferredoxin-dependent nitrate reductase. 862 15


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>