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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glutamine synthetase activity from Synechocystis sp. strain PCC 6803 is regulated as a function of the nitrogen source available in the medium. Addition of 0.25 mM NH4Cl to nitrate-grown cells promotes a clear short-term inactivation of glutamine synthetase, whose enzyme activity decreases to 5 to 10% of the initial value in 25 min. The intracellular levels of glutamine, determined under various conditions, taken together with the results obtained with azaserine (an inhibitor of transamidases), rule out the possibility that glutamine per se is responsible for glutamine synthetase inactivation. Nitrogen starvation attenuates the ammonium-mediated glutamine synthetase inactivation, indicating that glutamine synthetase regulation is modulated through the internal balance between carbon-nitrogen compounds and carbon compounds. The parallelism observed between the glutamine synthetase activity and the internal concentration of alpha-ketoglutarate suggests that this metabolite could play a role as a positive effector of glutamine synthetase activity in Synechocystis sp. Despite the similarities of this physiological system to that described for enterobacteria, the lack of in vivo 32P labeling of glutamine synthetase during the inactivation process excludes the existence of an adenylylation-deadenylylation system in this cyanobacterium.
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PMID:Regulation of glutamine synthetase activity in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 by the nitrogen source: effect of ammonium. 167 97

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 responds to combined nitrogen deprivation by forming specialized nitrogen-fixing cells at regular intervals along the filament. Genetic and biochemical studies have indicated that regulation of gene expression during differentiation occurs at the transcriptional level. As part of a characterization of RNA polymerase during differentiation, the gene encoding the 52-kDa principal sigma factor of the Anabaena sp. strain PCC 7120 vegetative-cell RNA polymerase was isolated by using an oligonucleotide probe based on the sequence of the N-terminal seven amino acids of the purified protein. sigA codes for a 390-amino-acid polypeptide that has a predicted molecular weight of 45,641. The amino acid sequence of the polypeptide encoded by sigA contains four regions corresponding to conserved domains of the principal RNA polymerase sigma factors of Escherichia coli (sigma 70) and Bacillus subtilis (sigma 43). Thus, although the subunit composition of cyanobacterial RNA polymerase core differs from that of other eubacteria (G. J. Schneider and R. Haselkorn, J. Bacteriol. 170:4136-4140, 1988), the principal sigma factor of at least one cyanobacterium is typically eubacterial. In contrast to sigma 70 and sigma 43 operon organization, sigA is monocistronic and encodes two transcripts of 1.7 and 2.2 kb. The abundance of the 1.7-kb transcript remains constant under both nitrogen-replete and nitrogen-limiting conditions, whereas the 2.2-kb transcript is induced following the removal of combined nitrogen. Continued or enhanced transcription of sigA under nitrogen starvation conditions is consistent with the observation that the principal RNA polymerase in differentiating cells contains SigA.
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PMID:Isolation and characterization of the gene encoding the principal sigma factor of the vegetative cell RNA polymerase from the cyanobacterium Anabaena sp. strain PCC 7120. 190 66

Using the cysA locus of Salmonella typhimurium as a heterologous probe, we have cloned a region of the Anacystis nidulans R2 (Synechococcus PCC 7942) genome involved in sulfate assimilation. The 8.3-kilobase-pair region encodes at least five transcripts that cannot be detected unless the cells are deprived of sulfur. One of the genes in this region has been sequenced, and the protein that it encodes is homologous to a polypeptide component of other permease systems of Escherichia coli and Salmonella. Insertional inactivation of the putative sulfate permease gene, designated cysA, as well as of other genes within this region, results in cysteine auxotrophy, reduced sulfate uptake, and altered expression of soluble and cytoplasmic-membrane polypeptides associated with sulfur starvation.
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PMID:A region of a cyanobacterial genome required for sulfate transport. 253 23

A genomic region from the filamentous, thermophilic non-N2-fixing cyanobacterium Phormidium laminosum was cloned and sequenced. It includes the nitrite reductase gene (nirA) and three other genes (nrtA, B and C) located downstream of nirA, which are related to the nitrate transport system on the basis of a comparison with the homologous system from Synechococcus sp. PCC 7942. No additional nitrate assimilation-related genes were identified in about 5 kb sequenced downstream of nrtC. All four genes are arranged as an operon with a promoter-like region upstream of the nirA gene. Transcripts of these nitrate assimilation genes accumulated after long periods of nitrogen starvation. This operon also contains inverted repeat sequences in the intercistronic regions which might be involved in mRNA processing or stability.
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PMID:Cloning and sequencing of the nitrate transport system from the thermophilic, filamentous cyanobacterium Phormidium laminosum: comparative analysis with the homologous system from Synechococcus sp. PCC 7942. 764 6

The upstream noncoding region of the Synechococcus sp. strain PCC 7942 (hereafter referred to as Synechococcus 7942) glnA gene was fused to the cat gene in order to study the expression of glnA both in Synechococcus 7942 and in Escherichia coli. The lack of cat expression in E. coli indicated that the glnA promoter was not recognized by E. coli RNA polymerase. The fused construct was integrated into the Synechococcus 7942 chromosome at a neutral site. Expression of the cat reporter gene was regulated under various nitrogen conditions in a way similar to that of the glnA gene. A deletion introduced at the binding site of the NtcA regulatory protein abolished derepression of the glnA promoter during growth in nitrate and under nitrogen starvation. Deletion of the sequence between the transcription and translation start sites of glnA prevented the repression observed during growth in ammonium. These results indicate that the glnA promoter is subject to complex regulation that involves sequences upstream and downstream from the transcription start site.
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PMID:Characterization of cis elements that regulate the expression of glnA in Synechococcus sp. strain PCC 7942. 772 15

The glnA gene, encoding type I glutamine synthetase (GS) in Synechocystis sp. PCC 6803, showed a high sequence similarity with other cyanobacterial glnA genes. A dramatic decrease in the amount of glnA mRNA, a single transcript of about 1.6 kb, was observed after transfer to darkness, or after incubation with the electron transport inhibitors DCMU or DBMIB. The levels of glnA transcript were fully recovered after 5 min of reillumination. The glnA mRNA was found to be equally stable both in the light and the dark (half-life about 2.5 min). Unlike the glnA messenger, the amount of GS protein was not reduced in the dark. Synthesis of the glnA transcript in the dark required the presence of glucose. In addition, glnA transcription in a Synechocystis psbE-psbF mutant lacking photosystem II required the presence of glucose even when grown in the light. These observations indicate that glnA transcription is under the control of the redox state of the cell. Finally, nitrogen starvation provoked a delay in the decrease of glnA transcript in darkness, suggesting a connection between nitrogen and redox controls of glnA transcript levels.
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PMID:Electron transport controls transcription of the glutamine synthetase gene (glnA) from the cyanobacterium Synechocystis sp. PCC 6803. 772 55

A stable DNA/protein complex having an apparent molecular mass of approximately 150 kDa was purified from nitrate-limited cultures of the cyanobacterium Synechococcus sp. strain PCC 7942. Amino-terminal peptide sequencing indicated that the polypeptide was structurally similar to the Dps protein of Escherichia coli; Dps is also known as the product of the starvation- and stationary-phase-inducible gene, pexB. The 150-kDa complex dissociated into a 22-kDa protein monomer after boiling in 2% SDS. The 150-kDa complex preparation had approximately a 10% nucleic acid content and upon dissociation released DNA fragments that were sensitive to S1 nuclease digestion. Immunoblot data indicated that the complex accumulates during stationary phase and during nitrogen, sulfur, and phosphorus limitation. DNA-binding assays indicated that the protein nonspecifically binds both linear and supercoiled DNA. Circular dichroism spectroscopy revealed that the Synechococcus sp. Dps-like protein contains extensive regions of alpha-helical secondary structure. We propose that the 150-kDa complex represents a hexameric aggregate of the Dps-like protein complexed with single-stranded DNA and serves to bind a portion of the chromosomal DNA under nutrient-limited conditions.
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PMID:Purification and characterization of a Synechococcus sp. strain PCC 7942 polypeptide structurally similar to the stress-induced Dps/PexB protein of Escherichia coli. 779 1

Strain 129 is a fragmentation mutant of the filamentous cyanobacterium Anabaena sp. strain PCC 7120. Growing with fixed nitrogen, this mutant forms filaments that are much shorter than wild-type filaments. Following starvation for fixed nitrogen, strain 129 becomes nearly unicellular and forms few heterocysts, although electron microscopy suggests that proheterocysts form while fragmentation occurs. Starvation for sulfate, phosphate, iron, and calcium does not cause this fragmentation. The affected gene in strain 129, fraC, was cloned by complementation and characterized. It encodes a unique 179-amino-acid protein rich in phenylalanine. Insertional inactivation of the chromosomal copy of fraC results in a phenotype identical to that of strain 129, while complementation using a truncated version of FraC results in only partial complementation of the original mutant. Heterocysts could be induced to form in N-replete cultures of strain 129, as in wild-type cells, by supplying extra copies of the hetR gene on a plasmid. Thus, FraC is required for the integrity of cell junctions in general but is apparently not directly involved in normal differentiation and nitrogen fixation.
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PMID:A short-filament mutant of Anabaena sp. strain PCC 7120 that fragments in nitrogen-deficient medium. 788 9

In Anabaena sp. strain PCC 7120, vegetative cell ferredoxin synthesis under iron starvation was repressed 25-fold, whereas heterocyst ferredoxin synthesis decreased only 2.8-fold. Induction of flavodoxin under iron depletion was independent of the availability of combined nitrogen. Under iron stress but in the presence of combined nitrogen, fdxH and nifH genes were transcriptionally active; although excision of the 11-kb element seemed to be completed, nitrogenase activity and the fdxH gene product were not detectable.
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PMID:Transcriptional and translational analysis of ferredoxin and flavodoxin under iron and nitrogen stress in Anabaena sp. strain PCC 7120. 796 17

Phycobilisomes are the multiprotein complexes predominantly responsible for harvesting light energy in cyanobacteria and some eukaryotic algae. When the cyanobacterium Synechococcus sp. strain PCC 7942 is deprived of an essential nutrient, the phycobilisomes are specifically and rapidly degraded. Degradation may be either partial (after phosphorus deprivation) or complete (after sulfur or nitrogen deprivation). We have developed a visual screen to obtain mutants unable to degrade their phycobilisomes upon nutrient starvation. Complementation of one of these mutants led to the identification of a gene, designated nblA, that encodes a 59 amino acid polypeptide essential for phycobilisome degradation. Transcription of nblA increases dramatically in sulfur- or nitrogen-deprived cells and moderately in phosphorus-deprived cells. Using the phosphorus-regulated alkaline phosphatase (phoA) promoter as a tool, we engineered constructs from which we could control the expression of either sense or antisense nblA. Increased expression of sense nbLA caused complete phycobilisome degradation during phosphorus deprivation, while expression of antisense nblA prevented phycobilisome degradation. Hence, nblA is necessary, and may be sufficient, for the degradation of phycobilisomes under adverse environmental conditions. Further investigation of the mechanism by which nblA causes phycobilisome destruction may reveal general principles that govern the specificity of macromolecular complex degradation.
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PMID:A small polypeptide triggers complete degradation of light-harvesting phycobiliproteins in nutrient-deprived cyanobacteria. 813 38


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