The Experts below are selected from a list of 969 Experts worldwide ranked by ideXlab platform
Jean Houmard - One of the best experts on this subject based on the ideXlab platform.
-
Promoter recognition by a cyanobacterial RNA polymerase: in vitro studies with the Calothrix sp. PCC 7601 transcriptional factors RcaA and RcaD
Plant Molecular Biology, 1998Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Lin Jia, Thérèse Coursin, Jean HoumardAbstract:To study the transcriptional apparatus and the mechanisms that control gene expression in cyanobacteria, the RNA polymerase was purified from the filamentous Calothrix sp. PCC 7601 and used in in vitro transcription assays. Conditions required for specific transcription initiation to occur were analyzed with the eleven Calothrix PCC 7601 genes for which the 5′ ends have been mapped. Most of the transcripts directly obtained did not have the expected size, providing a test for looking at specific transcription factors. Addition of RcaA, a protein that binds to the promoter region of the phycobiliprotein cpeBA operon, restored accurate initiation of transcription in the in vitro system for three phycobiliprotein promoters. RcaA thus is a transcription factor that allows to mimick in vivo transcription. In parallel, the functional properties of the Escherichia coli and cyanobacterial RNA polymerases were compared. The enteric enzyme could not precisely initiate transcription at the promoter of a phycobiliprotein gene and, reciprocally, the cyanobacterial RNA polymerase could initiate transcription at P_lacUV5, but not from wild-type P_lac promoters. The different behaviours of the enzymes are discussed in the light of the structural differences that exist between subunits of the RNA polymerases.
-
specific initiation of transcription at a cyanobacterial promoter with rna polymerase purified from Calothrix sp pcc 7601
Molecular Microbiology, 1994Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Andre Sobczyk, Jean HoumardAbstract:Summary Although in cyanobacteria many genes have been shown to be transcriptionally controlled by specific stimuli, little is known about promoter structure and the form of RNA polymerase that recognizes individual promoters. RNA polymerase holoenzyme has been purified from Calothrix sp. PCC 7601. its polypeptide composition resembles that of the plant chloroplast enzymes. To study transcription in cyanobacteria further, we have analysed the promoter-recognition properties of the purified enzyme. In vitro transcription was assayed with the promoter of the phycocyanin gene (cpc1) that is expressed whatever the incident light conditions. Transcription initiation at the same start point as in vivo was obtained with the Calothrix sp. PCC 7601 purified enzyme and the Escherichia coli core enzyme supplemented with a Calothrix sp. PCC 7601 sigma factor, but not with the E. coli holoenzyme.
-
electron transport regulates cellular differentiation in the filamentous cyanobacterium Calothrix
The Plant Cell, 1993Co-Authors: Douglas A Campbell, Jean Houmard, N T De MarsacAbstract:Differentiation of the filamentous cyanobacteria Calothrix sp strains PCC 7601 and PCC 7504 is regulated by light spectral quality. Vegetative filaments differentiate motile, gas-vacuolated hormogonia after transfer to fresh medium and incubation under red light. Hormogonia are transient and give rise to vegetative filaments, or to heterocystous filaments if fixed nitrogen is lacking. If incubated under green light after transfer to fresh medium, vegetative filaments do not differentiate hormogonia but may produce heterocysts directly, even in the presence of combined nitrogen. We used inhibitors of thylakoid electron transport (3-[3,4-dichlorophenyl]-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) to show that the opposing effects of red and green light on cell differentiation arise through differential excitations of photosystems I and II. Red light excitation of photosystem I oxidizes the plastoquinone pool, stimulating differentiation of hormogonia and inhibiting heterocyst differentiation. Conversely, net reduction of plastoquinone by green light excitation of photosystem II inhibits differentiation of hormogonia and stimulates heterocyst differentiation. This photoperception mechanism is distinct from the light regulation of complementary chromatic adaptation of phycobilisome constituents. Although complementary chromatic adaptation operates independently of the photocontrol of cellular differentiation, these two regulatory processes are linked, because the general expression of phycobiliprotein genes is transiently repressed during hormogonium differentiation. In addition, absorbance by phycobilisomes largely determines the light wavelengths that excite photosystem II, and thus the wavelengths that can imbalance electron transport.
-
molecular characterization of the gene encoding glutamine synthetase in the cyanobacterium Calothrix sp pcc 7601
Biochemical and Biophysical Research Communications, 1992Co-Authors: Khalil Elmorjani, Jean Houmard, Sylviane Liotenberg, Nicole Tandeau De MarsacAbstract:In order to study the regulation of the synthesis of glutamine synthetase in response to changes in environmental parameters (light and nitrogen sources), we have cloned and sequenced the glnA gene from the filamentous cyanobacterium Calothrix PCC 7601. This gene consists of 472 codons and encodes a polypeptide of M(r) 52,290 highly homologous to that from Anabaena PCC 7120, but more distant from those identified from other procaryotes. The relative abundance of the two glnA transcripts (1.6 and 1.8 kb) is equivalent in cells grown under either red or green light, but the 1.6-kb species predominates in nitrate-grown cells and the 1.8-kb species in ammonia-grown cells. The very high identity (74%) observed between the 374-bp long nucleotide sequence upstream from the Calothrix and Anabaena glnA genes suggests the existence of similar regulatory signals for the control of glnA expression in both cyanobacteria.
-
characterization of two insertion sequences is701 and is702 from the cyanobacterium Calothrix species pcc 7601
Molecular Microbiology, 1991Co-Authors: Didier Mazel, Jean Houmard, A M Castets, Cecile Bernard, Rakefet Schwarz, Tandeau N De MarsacAbstract:We describe the characterization of two insertion elements, IS701 and IS702, isolated from Calothrix species PCC 7601. These insertion elements were cloned from spontaneous pigmentation mutants. Both show the characteristics of typical bacterial insertion sequences, i.e. they present long terminal inverted repeats and they duplicate target DNA upon insertion. These elements share no homology with the only other cyanobacterial insertion sequence described so far, IS891. At least 15 copies of IS701 and 9 copies of IS702 were detected by hybridization experiments in the Calothrix 7601 genome. Their occurrence in several cyanobacterial strains is also reported.
Nicole Tandeau De Marsac - One of the best experts on this subject based on the ideXlab platform.
-
Promoter recognition by a cyanobacterial RNA polymerase: in vitro studies with the Calothrix sp. PCC 7601 transcriptional factors RcaA and RcaD
Plant Molecular Biology, 1998Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Lin Jia, Thérèse Coursin, Jean HoumardAbstract:To study the transcriptional apparatus and the mechanisms that control gene expression in cyanobacteria, the RNA polymerase was purified from the filamentous Calothrix sp. PCC 7601 and used in in vitro transcription assays. Conditions required for specific transcription initiation to occur were analyzed with the eleven Calothrix PCC 7601 genes for which the 5′ ends have been mapped. Most of the transcripts directly obtained did not have the expected size, providing a test for looking at specific transcription factors. Addition of RcaA, a protein that binds to the promoter region of the phycobiliprotein cpeBA operon, restored accurate initiation of transcription in the in vitro system for three phycobiliprotein promoters. RcaA thus is a transcription factor that allows to mimick in vivo transcription. In parallel, the functional properties of the Escherichia coli and cyanobacterial RNA polymerases were compared. The enteric enzyme could not precisely initiate transcription at the promoter of a phycobiliprotein gene and, reciprocally, the cyanobacterial RNA polymerase could initiate transcription at P_lacUV5, but not from wild-type P_lac promoters. The different behaviours of the enzymes are discussed in the light of the structural differences that exist between subunits of the RNA polymerases.
-
specific initiation of transcription at a cyanobacterial promoter with rna polymerase purified from Calothrix sp pcc 7601
Molecular Microbiology, 1994Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Andre Sobczyk, Jean HoumardAbstract:Summary Although in cyanobacteria many genes have been shown to be transcriptionally controlled by specific stimuli, little is known about promoter structure and the form of RNA polymerase that recognizes individual promoters. RNA polymerase holoenzyme has been purified from Calothrix sp. PCC 7601. its polypeptide composition resembles that of the plant chloroplast enzymes. To study transcription in cyanobacteria further, we have analysed the promoter-recognition properties of the purified enzyme. In vitro transcription was assayed with the promoter of the phycocyanin gene (cpc1) that is expressed whatever the incident light conditions. Transcription initiation at the same start point as in vivo was obtained with the Calothrix sp. PCC 7601 purified enzyme and the Escherichia coli core enzyme supplemented with a Calothrix sp. PCC 7601 sigma factor, but not with the E. coli holoenzyme.
-
molecular characterization of the gene encoding glutamine synthetase in the cyanobacterium Calothrix sp pcc 7601
Biochemical and Biophysical Research Communications, 1992Co-Authors: Khalil Elmorjani, Jean Houmard, Sylviane Liotenberg, Nicole Tandeau De MarsacAbstract:In order to study the regulation of the synthesis of glutamine synthetase in response to changes in environmental parameters (light and nitrogen sources), we have cloned and sequenced the glnA gene from the filamentous cyanobacterium Calothrix PCC 7601. This gene consists of 472 codons and encodes a polypeptide of M(r) 52,290 highly homologous to that from Anabaena PCC 7120, but more distant from those identified from other procaryotes. The relative abundance of the two glnA transcripts (1.6 and 1.8 kb) is equivalent in cells grown under either red or green light, but the 1.6-kb species predominates in nitrate-grown cells and the 1.8-kb species in ammonia-grown cells. The very high identity (74%) observed between the 374-bp long nucleotide sequence upstream from the Calothrix and Anabaena glnA genes suggests the existence of similar regulatory signals for the control of glnA expression in both cyanobacteria.
-
Hormogonium Differentiation in the Cyanobacterium Calothrix: A Photoregulated Developmental Process.
The Plant Cell, 1991Co-Authors: T. Damerval, Gerard Guglielmi, Jean Houmard, Nicole Tandeau De MarsacAbstract:Hormogonium differentiation is part of the developmental cycle in many heterocystous cyanobacteria. Hormogonia are involved in the dispersal and survival of the species in its natural habitat. The formation of these differentiated filaments has been shown to depend on several environmental conditions, including spectral light quality. We report here morphological and ultrastructural changes associated with the formation of hormogonia, as well as optimal light conditions required for their differentiation in the cyanobacterium Calothrix sp PCC 7601. The action spectrum for hormogonium differentiation is similar to that which triggers complementary chromatic adaptation because red and green radiation display antagonistic effects in both cases. However, these two photoregulated processes also show major differences. Transcription analyses of genes that are specifically expressed during hormogonium differentiation, as well as of genes encoding phycobiliproteins, suggest that two different photoregulatory pathways may exist in this cyanobacterium.
Richard W Castenholz - One of the best experts on this subject based on the ideXlab platform.
-
UV-acclimation responses in natural populations of cyanobacteria (Calothrix sp.).
Environmental Microbiology, 2003Co-Authors: Jesse G. Dillon, Scott R Miller, Richard W CastenholzAbstract:Summary Phenotypic acclimation to changing conditions is typically thought to be beneficial to organisms in the environment. UV radiation is an important parameter affecting photosynthetic organisms in natural environments. We measured the response of photosynthetic carbon fixation in populations of cyanobacteria inhabiting a hot spring following acclimation to different UV treatments. These two very closely related populations of cyanobacteria, differing in their content of the extracellular UV-screening pigment scytonemin, were acclimated in situ under natural solar irradiance modified by filters that excluded both UVA/B, only UVB or transmitted both UVA/B. Cells from each preacclimation treatment were subsequently assayed for photosynthetic performance under all UV conditions (incubation treatment) giving a two-factor experimental design for each population. No acclimation filter treatment effects were observed even after two months under different acclimation treatments. This suggests that UV photoacclimation does not occur in either of these populations, regardless of the presence of scytonemin. By contrast, cells showed significant UV-inhibition during 1 h incubations under full sun. The population with high levels of scytonemin usually had lower rates of photosynthetic carbon fixation than the scytonemin-lacking population. However, the degree of UV inhibition, especially UVA inhibition, was higher for the cells without scytonemin pigment. These results suggest that closely related natural cyanobacterial populations respond differently to natural irradiance conditions and may be adopting different strategies of UV tolerance.
-
the synthesis of the uv screening pigment scytonemin and photosynthetic performance in isolates from closely related natural populations of cyanobacteria Calothrix sp
Environmental Microbiology, 2003Co-Authors: Jesse G. Dillon, Richard W CastenholzAbstract:Summary Two populations of the cyanobacterium Calothrix sp. found in Yellowstone thermal spring outflows differ greatly in their contents of scytonemin, a UV-screen- ing pigment, and in their photosynthetic carbon assimilation rates. Clonal isolates from both popula- tions were used to investigate these phenotypic dif- ferences. Identical partial 16S rDNA sequences ( ~ 900 bp) suggest a very close relationship between the two Calothrix populations and indicate that envi- ronmental differences may, in part, explain the field observations. The effects of native spring water on scytonemin synthesis and photosynthesis were tested during experiments using plated cells. Results show differences in the spring water environment were at least partly responsible for the differences in scytonemin content observed in the field. Further- more, spring water effects on photosynthetic perfor- mance suggest adaptation in these strains to their spring of origin. Controlled experiments performed using cultures grown in artificial liquid medium showed no significant difference in photosynthetic carbon uptake between strains. However, significant differences were detected in their ability to synthesize scytonemin indicating genetic differences between populations. These findings suggest that both genetic and environmental differences are responsible for the naturally occurring variation in scytonemin content and photosynthetic ability in these two closely related populations.
-
long term effects of uv and visible irradiance on natural populations of a scytonemin containing cyanobacterium Calothrix sp
FEMS Microbiology Ecology, 1997Co-Authors: Stephan D Brenowitz, Richard W CastenholzAbstract:A natural warm spring stream with a cyanobacterial biofilm community composed almost entirely of Calothrix sp., a species rich in the UV-absorbing sheath pigment scytonemin, was used for 3 month summer experiments to test the following hypotheses: (1) UV radiation is necessary for the synthesis of high scytonemin content in sheaths. (2) High scytonemin content is required for uninhibited photosynthesis under high UV flux. Both of these hypotheses were answered affirmatively in earlier experiments with laboratory cultures of other cyanobacterial species. However, the tests of these hypotheses under natural conditions were necessary to confirm these conclusions, mainly because fluxes of UV and visible radiation and their ratios are very different under field conditions. Intact mats of Calothrix, siliceous substrate cleared of Calothrix, and artificial foam were treated for 3 months under filters transparent to UV radiation and visible light, and under filters that excluded only UV radiation. Neutral density screens were used in combination with filters to reduce the total irradiance over some sections of the stream. After 3 months, under all treatments, the predominant organism was still the same morphotype of Calothrix. Intact Calothrix mats produced high levels of scytonemin over the summer, except under low UV and low visible irradiance, while chlorophyll-a values per unit area remained relatively low and showed little change under all treatments. After 3 months, intact Calothrix mat and colonized mat with substantial scytonemin were not inhibited photosynthetically by UV irradiance. Only colonized populations exposed to ∼12% UV and ∼12% visible irradiance, and with very low scytonemin content, showed significant UV-inhibition. Thus, the correlation between UV protection and scytonemin presence was established experimentally for the first time under solar irradiance in a natural, essentially monospecific population of a cyanobacterium.
Ghislain Schyns - One of the best experts on this subject based on the ideXlab platform.
-
Promoter recognition by a cyanobacterial RNA polymerase: in vitro studies with the Calothrix sp. PCC 7601 transcriptional factors RcaA and RcaD
Plant Molecular Biology, 1998Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Lin Jia, Thérèse Coursin, Jean HoumardAbstract:To study the transcriptional apparatus and the mechanisms that control gene expression in cyanobacteria, the RNA polymerase was purified from the filamentous Calothrix sp. PCC 7601 and used in in vitro transcription assays. Conditions required for specific transcription initiation to occur were analyzed with the eleven Calothrix PCC 7601 genes for which the 5′ ends have been mapped. Most of the transcripts directly obtained did not have the expected size, providing a test for looking at specific transcription factors. Addition of RcaA, a protein that binds to the promoter region of the phycobiliprotein cpeBA operon, restored accurate initiation of transcription in the in vitro system for three phycobiliprotein promoters. RcaA thus is a transcription factor that allows to mimick in vivo transcription. In parallel, the functional properties of the Escherichia coli and cyanobacterial RNA polymerases were compared. The enteric enzyme could not precisely initiate transcription at the promoter of a phycobiliprotein gene and, reciprocally, the cyanobacterial RNA polymerase could initiate transcription at P_lacUV5, but not from wild-type P_lac promoters. The different behaviours of the enzymes are discussed in the light of the structural differences that exist between subunits of the RNA polymerases.
-
specific initiation of transcription at a cyanobacterial promoter with rna polymerase purified from Calothrix sp pcc 7601
Molecular Microbiology, 1994Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Andre Sobczyk, Jean HoumardAbstract:Summary Although in cyanobacteria many genes have been shown to be transcriptionally controlled by specific stimuli, little is known about promoter structure and the form of RNA polymerase that recognizes individual promoters. RNA polymerase holoenzyme has been purified from Calothrix sp. PCC 7601. its polypeptide composition resembles that of the plant chloroplast enzymes. To study transcription in cyanobacteria further, we have analysed the promoter-recognition properties of the purified enzyme. In vitro transcription was assayed with the promoter of the phycocyanin gene (cpc1) that is expressed whatever the incident light conditions. Transcription initiation at the same start point as in vivo was obtained with the Calothrix sp. PCC 7601 purified enzyme and the Escherichia coli core enzyme supplemented with a Calothrix sp. PCC 7601 sigma factor, but not with the E. coli holoenzyme.
Lin Jia - One of the best experts on this subject based on the ideXlab platform.
-
Promoter recognition by a cyanobacterial RNA polymerase: in vitro studies with the Calothrix sp. PCC 7601 transcriptional factors RcaA and RcaD
Plant Molecular Biology, 1998Co-Authors: Ghislain Schyns, Nicole Tandeau De Marsac, Lin Jia, Thérèse Coursin, Jean HoumardAbstract:To study the transcriptional apparatus and the mechanisms that control gene expression in cyanobacteria, the RNA polymerase was purified from the filamentous Calothrix sp. PCC 7601 and used in in vitro transcription assays. Conditions required for specific transcription initiation to occur were analyzed with the eleven Calothrix PCC 7601 genes for which the 5′ ends have been mapped. Most of the transcripts directly obtained did not have the expected size, providing a test for looking at specific transcription factors. Addition of RcaA, a protein that binds to the promoter region of the phycobiliprotein cpeBA operon, restored accurate initiation of transcription in the in vitro system for three phycobiliprotein promoters. RcaA thus is a transcription factor that allows to mimick in vivo transcription. In parallel, the functional properties of the Escherichia coli and cyanobacterial RNA polymerases were compared. The enteric enzyme could not precisely initiate transcription at the promoter of a phycobiliprotein gene and, reciprocally, the cyanobacterial RNA polymerase could initiate transcription at P_lacUV5, but not from wild-type P_lac promoters. The different behaviours of the enzymes are discussed in the light of the structural differences that exist between subunits of the RNA polymerases.
-
adaptation de la cyanobacterie Calothrix pcc 7601 a son environnement caracterisation de deux elements de regulation rcaa et cyaa
1996Co-Authors: Lin JiaAbstract:Les cyanobacteries sont des procaryotes qui effectuent les reactions de la photosynthese en degageant de l'oxygene. Parmi elles, la souche filamenteuse Calothrix pcc 7601 possede des proprietes physiologiques remarquables: elle est photoheterotrophe facultative, elle possede de plus les genes nif et peut differencier des proheterocystes ; elle peut aussi differencier des hormogonies, petites cellules mobiles remplies de vesicules a gaz conferant aux cellules une flottabilite ; enfin, elle peut moduler la nature des pigments de ses antennes photocollectrices (phycobilisomes) selon la qualite spectrale de la lumiere (adaptation chromatique complementaire). En lumiere rouge, les cellules contiennent de la phycocyanine-2 (operon cpc2), tandis qu'en lumiere verte elles contiennent de la phycoerythrine (operons cpe). Cette adaptation resulte d'un controle transcriptionnel des operons correspondants, rcaa et rcab en lumiere verte pour cpeba, rcad en lumiere rouge pour cpc2 etant des proteines affines specifiques. Une methode de purification a ete developpee qui a permis d'obtenir une preparation tres homogene de la proteine rcaa. Par des experiences de transcription in vitro controlee, nous avons montre que rcaa modifiait l'efficacite et la specificite de transcription pour au moins quatre promoteurs d'operons codant pour des phycobiliproteines, et que les proprietes de rcaa en tant que facteur de transcription etaient affectees par son etat de phosphorylation. A partir de la sequence de peptides internes a rcaa, et par des experiences d'amplification de type pcr, le gene rcaa a ete clone. Apres sequencage, il est apparu que rcaa presente beaucoup d'homologie avec les glutamyl tarn synthetases (gltx), observation dont les consequences sont discutees. Un modele est propose pour la regulation transcriptionnelle de l'expression des operons codant pour les composants majeurs des phycobilisomes, lors de l'adaptation chromatique complementaire chez Calothrix pcc 7601. Enfin, le gene cyaa de Calothrix pcc 7601 a ete caracterise. Il code pour une adenylate cyclase (686 residus) de classe iii (universelle) de structure tres originale, la partie n-terminale (aa 1-260) et la partie centrale (aa 321-450) formant deux domaines, respectivement tres similaires aux histidine kinases (sensors) et aux transmetteurs (response regulators) des systemes a deux composants tres repandus dans le monde bacterien
