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J Houmard

Publications and source records attributed to J Houmard.

At least 37 records · Page 2Linked to original sources
PubMed1991

Gas vesicle synthesis in the cyanobacterium Pseudanabaena sp.: occurrence of a single photoregulated gene.

Gas vesicles are subcellular inclusions found in a large number of aquatic prokaryotes. The gvpA gene, which frequently occurs as a multigene family, encodes the major gas vesicle structural protein. In several cyanobacteria, another gene, gvpC, encodes a different protein which might be a dispensable element for gas vesicle formation. We report here the molecular characterization of a gvpA gene in Pseudanabaena sp. PCC 6901. In this planktonic cyanobacterium, it is the only gvp gene which could be detected, and electrophoretic analysis of isolated gas vesicles revealed the presence of a single protein. A monocistronic mRNA species corresponds to the transcription of the gvpA gene and the abundance of the gvpA mRNA is inversely correlated with photosynthetic photon flux indicating that a light-dependent transcriptional regulation is likely to be involved in the control of gas vacuolation in this strain.

Amino Acid Sequence↗
PubMed1991

Characterization of two insertion sequences, IS701 and IS702, from the cyanobacterium Calothrix species PCC 7601.

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.

Amino Acid Sequence↗
PubMed1990

Blood lactate threshold differences between arterialized and venous blood.

The purpose of this study was to investigate the differences between lactate thresholds determined from venous and arterialized blood. Seven endurance-trained college males performed an incremental bicycle ergometer exercise test until exhaustion. At the end of each 3 min stage, blood was sampled simultaneously from a hyperemized ear-lobe and an antecubital vein for the measurement of blood lactate (La-). Two-minute rest intervals separated each stage. Arterialized blood La-concentrations ([La-]) were significantly higher than venous blood at 350 W (14.5 and 9.7 mmol.l-1), maximal exercise (15.5 and 11.39 mmol.l-1), and throughout recovery. Arterialized [La-] was significantly higher than venous blood at the onset of blood La- accumulation (OBLA) (4.0 and 2.8 +/- 0.1 mmol.l-1), the individual anaerobic threshold (IAT) (3.4 +/- 0.3 and 2.1 +/- 0.1 mmol.l-1), and the ventilatory threshold (VT) (4.7 +/- 0.9 and 3.2 +/- 0.6 mmol.l-1). No significant differences were found between either La-threshold for arterialized or venous blood. The oxygen consumption (VO2) at OBLA was significantly lower when determined from arterialized blood La (2.3 +/- 0.2 and 2.8 +/- 0.2 l.min-1). No significant differences existed between the LT, OBLA, and IAT threshold-VO2 determinations from arterialized blood; however, significant differences were found between IAT-OBLA (2.1 +/- 0.2 and 2.8 +/- 0.2 l.min-1) and LT (2.2 +/- 0.2 l.min-1)-OBLA from venous blood. These results indicate that differences between venous and arterialized blood [La-] need to be considered when comparing different anaerobic threshold determinations.

Adult↗
PubMed1990

Molecular characterization of the terminal energy acceptor of cyanobacterial phycobilisomes.

Cyanobacteria harvest light energy through multimolecular structures, the phycobilisomes, regularly arrayed at the surface of the photosynthetic membranes. Phycobilisomes consist of a central core from which rods radiate. A large polypeptide (LCM, 75-120 kDa) is postulated to act both as terminal energy acceptor and as a linker polypeptide that stabilizes the phycobilisome architecture. We report here the characterization of the gene (apcE) that encodes this LCM polypeptide in Calothrix sp. PCC 7601. It is located upstream from the genes encoding the major components of the phycobilisome core (allophycocyanin) and is part of the same operon. The deduced amino acid sequence shows that the N-terminal region of LCM shares homology with the other phycobiliprotein subunits and thus constitutes the chromoprotein domain. The other part of the molecule is made up of four repeated domains that are highly homologous to the N-terminal regions of the phycocyanin rod linker polypeptides. The predicted secondary structure of the different domains of the LCM is discussed in relation to the different roles and properties of this large molecule.

Amino Acid Sequence↗
PubMed1990

Highly repetitive DNA sequences in cyanobacterial genomes.

We characterized three distinct families of repeated sequences in the genome of the cyanobacterium Calothrix sp. strain PCC 7601. These repeated sequences were present at a level of about 100 copies per Calothrix genome and consisted of tandemly amplified heptanucleotides. These elements were named short tandemly repeated repetitive (STRR) sequences. We used the three different Calothrix STRR sequences as probes to perform Southern hybridization experiments with DNAs extracted from various cyanobacterial strains, Bacillus subtilis, and Escherichia coli. The three different STRR sequences were found as repetitive genomic DNA components specific to the heterocystous strains tested. The role of the STRR sequences, as well as their possible use in taxonomic studies, is discussed.

Bacillus subtilis↗
PubMed1989

Occurrence and distribution of gas vesicle genes among cyanobacteria.

Gas vesicles (GV) are specialized cell inclusions providing many aquatic procaryotes with buoyancy. In the cyanobacterium Calothrix sp. strain PCC 7601, at least four genes are involved in GV formation. One of those, gvpA1, encodes the major structural GV protein (70 amino acids) and belongs to a multigene family (gvpA1, gvpA2, gvpD). The fourth gene, gvpC, encodes a 162-amino-acid protein, the function of which is still unclear. We used the Calothrix gvpA1 and gvpC genes as probes to perform Southern hybridization experiments with DNA extracted from various cyanobacterial strains. The gvpA gene was found in all the strains that synthesize GV, indicating that its product is an obligatory component of GV. Furthermore, it was found to occur as multiple copies in most of the strains tested. The gvpC gene was only detected in some strains able to synthesize a large amount of GV within a short period. This suggests that the gvpC gene product is a dispensable protein for GV formation and is involved in the efficiency of the assembly process. Based on the occurrence of the gvp genes and on DNA-DNA hybridization patterns, genus assignments are discussed.

Bacterial Proteins↗
PubMed1988

Genes encoding core components of the phycobilisome in the cyanobacterium Calothrix sp. strain PCC 7601: occurrence of a multigene family.

The phycobilisome is the major light-harvesting complex of cyanobacteria. It is composed of a central core from which six rods radiate. Allphycocyanin, an alpha beta oligomer (alpha AP and beta AP), is the main component of the core which also contains three other phycobiliproteins (alpha APB, beta 18.3, and L92CM) and a small linker polypeptide (L7.8C). By heterologous DNA hybridization, two EcoRI DNA fragments of 3.5 and 3.7 kilobases have been cloned from the chromatically adapting cyanobacterium Calothrix sp. strain PCC 7601. Nucleotide sequence determination has allowed the identification of five apc genes: apcA1 (alpha AP1), apcA2 (alpha AP2), apcB1 (beta AP1), apcC (L7.8C), and apcE (L92CM). Four of these genes are adjacent on the chromosome and form the apcEA1B1C gene cluster. In contrast, no genes have been found close to the apcA2 gene which is carried by the 3.5-kilobase EcoRI fragment. Transcriptional analysis and 5'-end-mapping experiments were performed. The results obtained demonstrate that the apcEA1B1C gene cluster forms an operon from which segmented transcripts originate, whereas the apcA2 gene behaves as a monocistronic unit. Qualitatively, the same transcripts were identified regardless of the light wavelengths received during cell growth. The deduced amino acid sequences of the apc gene products are very similar to their known homologs of either cyanobacterial or eucaryotic origin. It was interesting, however, that in the apcA1 and apcA2 genes, whose products correspond to alpha-type allophycocyanin subunits, nucleotide sequences were more conserved (67%) than were the deduced amino acid sequences (59%).

Amino Acid Sequence↗
PubMed1988

Isolation and molecular characterization of the gene encoding allophycocyanin B, a terminal energy acceptor in cyanobacterial phycobilisomes.

Phycobilisomes are the major constituents of the light-harvesting apparatus in both cyanobacteria and red algae and consist of a central core with radiating rods. From a genomic library of the cyanobacterium Calothrix 7601, a DNA fragment encoding allophycocyanin B, one of the two terminal energy acceptors of the core, was isolated and its nucleotide sequence was determined. Unlike all the other known genes encoding phycobiliproteins, the allophycocyanin B gene, apcD, is transcribed as a monocistronic unit. Mapping of the transcripts was performed and, in contrast to some of the Calothrix genes that encode rod components, transcription was shown to occur regardless of chromatic light received during cell growth.

Amino Acid Sequence↗
PubMed1987

Transcriptional analysis of the cyanobacterial gvpABC operon in differentiated cells: occurrence of an antisense RNA complementary to three overlapping transcripts.

Cyanobacteria are photosynthetic prokaryotes able to colonize almost all kinds of ecosystems. Some of them exhibit differentiation processes and/or may establish tight symbiotic associations. Upon changes in the environmental conditions, the cyanobacterium Calothrix 7601 differentiates hormogonia which are short filaments of small cells resulting from cellular division and fragmentation of the long filaments of vegetative cells. In Calothrix, hormogonia are characterized by their gliding motility and by a massive production of gas vesicles which confer buoyancy. At least four genes are involved in the formation of gas vesicles, three of which are organized in one operon (gvpABC). Four different RNA species, only present after induction of hormogonia differentiation, result from transcription of this operon. Mapping of the 5' and 3' ends of these transcripts demonstrates the presence of gvpA, gvpAB and gvpABC transcripts, all three having the same 5' end. Each of the three transcripts terminates a few bases downstream from stem-and-loop structures. Most interestingly, the fourth transcript is an antisense RNA starting from the 3' end of the gvpB gene and ending within the gvpA gene. This antisense RNA can thus form an homologous duplex with the three other transcripts, thereby being able to impair translation and/or modify mRNA stability.

Chromosome Mapping↗
PubMed1987

A developmentally regulated gvpABC operon is involved in the formation of gas vesicles in the cyanobacterium Calothrix 7601.

In the filamentous cyanobacterium Calothrix PCC7601, gas-vesicle (GV) formation is restricted to specialized filaments, called hormogonia. The differentiation of these cells is controlled by environmental factors, such as light intensity and/or wavelength. The structural gene (gvpA) encoding a GV protein in this cyanobacterium has been previously cloned and sequenced. Two other genes, gvpB and gvpC have been found in the sequence downstream from gvpA. The gvpB gene corresponds to a second copy of gvpA, encoding an identical protein. Unlike the GV protein, the product of the gvpC gene is predominantly hydrophilic, as deduced from nucleotide sequence. Interestingly, the internal part of the gvpC gene is composed of four contiguous repeats, each containing 99 bp, forming highly homologous repeats in the deduced amino acid sequence. Another kind of periodicity has been detected inside the 99-bp repeats, suggesting that the gvpC gene might have evolved by amplification of a 33-bp-long primordial building block. The function of this gene remains to be elucidated. Finally, we have shown that the three genes, gvpA, gvpB, and gvpC, are organized in an operon that is exclusively expressed during GV formation in hormogonia.

Amino Acid Sequence↗
PubMed1987

Improvements in exercise performance: effects of carbohydrate feedings and diet.

In an effort to determine the effects of carbohydrate (CHO) feedings immediately before exercise in both the fasted and fed state, 10 well-trained male cyclists [maximum O2 consumption (VO2 max), 4.35 +/- 0.11 l/min)] performed 45 min of cycling at 77% VO2 max followed by a 15-min performance ride on an isokinetic cycle ergometer. After a 12-h fast, subjects ingested 45 g of liquid carbohydrate (LCHO), solid carbohydrate confectionery bar (SCHO), or placebo (P) 5 min before exercise. An additional trial was performed in which a high-CHO meal (200 g) taken 4 h before exercise was combined with a confectionery bar feeding (M + SCHO) immediately before the activity. At 10 min of exercise, serum glucose values were elevated by 18 and 24% during SCHO and LCHO, respectively, compared with P. At 0 and 45 min no significant differences were observed in muscle glycogen concentration or total use between the four trials. Total work produced during the final 15 min of exercise was significantly greater (P less than 0.05) during M + SCHO (194,735 +/- 9,448 N X m), compared with all other trials and significantly greater (P less than 0.05) during LCHO and SCHO (175,204 +/- 11,780 and 176,013 +/- 10,465 N X m, respectively) than trial P (159,143 +/- 11,407 N X m). These results suggest that, under conditions when CHO stores are less than optimal, exercise performance is enhanced with the ingestion of 45 g of CHO 5 min before 1 h of intense cycling.(ABSTRACT TRUNCATED AT 250 WORDS)

Bicycling↗
PubMed1986

Green light induces transcription of the phycoerythrin operon in the cyanobacterium Calothrix 7601.

Phycobilisomes, the major light-harvesting complexes of cyanobacteria are multimolecular structures made up of chromophoric proteins called phycobiliproteins and non chromophoric linker polypeptides. We report here the isolation and nucleotide sequence of the genes, cpeA and cpeB, which in Calothrix PCC 7601 encode the alpha and beta subunits of phycoerythrin, one of the major phycobiliproteins. In Calothrix PCC 7601, modulation of the polypeptide composition of the phycobilisomes occurs in response to changes of the light wavelength, a phenomenon known as complementary chromatic adaptation. Under green illumination, cells synthesize phycoerythrin and its two specifically associated linker polypeptides (LR35 and LR36), while under red illumination none of these proteins are detected. Using specific probes, a single transcript (1450 nucleotide long) corresponding to the cpe genes was detected but only in green-light-grown cells, establishing the occurrence of transcriptional regulation for the expression of this operon in response to light wavelength changes. The size of this transcript excludes the possibility that the phycoerythrin-associated LR35 and LR36 could be cotranscribed with the cpeA and cpeB genes.

Amino Acid Sequence↗
PubMed1986

Organization and nucleotide sequence of genes encoding core components of the phycobilisomes from Synechococcus 6301.

Cyanobacteria possess specialized organelles, called phycobilisomes, which collect and transfer light energy to the reaction centres of photosystem II, in the photosynthetic membrane. Phycobilisomes consist of a central core, mainly composed of allophycocyanin, from which six rods radiate. We report here the isolation, for the first time, of three genes that encode core components of cyanobacterial phycobilisomes. The genes coding for the alpha- and beta-subunit apoproteins of allophycocyanin (apcA and apcB) were cloned from Synechococcus PCC 6301 and subjected to nucleotide sequence analysis. Dowstream of apcB, we found a third open reading frame (apcC) which, by comparison with known amino acid sequences, was assigned to L7.8c, a linker polypeptide associated with phycobiliproteins within the core of the phycobilisomes. Homologies between amino acid sequences deduced from the nucleotide sequence of the Synechococcus PCC 6301 apc genes and the amino acid sequences published for corresponding proteins either from cyanobacteria or chloroplast-like organelles of eukaryotic organisms, are 75% or more. The genetic organization of this photosynthetic gene cluster relative to that observed in the cyanelle genome of the flagellate Cyanophora paradoxa is discussed.

Amino Acid Sequence↗
PubMed1985

Molecular cloning and nucleotide sequence of a developmentally regulated gene from the cyanobacterium Calothrix PCC 7601: a gas vesicle protein gene.

Since the gas vesicle protein (GVP) is highly conserved among the different gas-vacuolate prokaryotes, a 29-mer oligonucleotide corresponding to a portion of the Anabaena flos-aquae GVP gene was synthesized and used to isolate the GVP structural gene from Calothrix PCC 7601 (= Fremyella diplosiphon). Gas vacuole production in this filamentous cyanobacterium is restricted to hormogonia which occur at a specific stage during the developmental cell cycle. The GVP gene (gvpA) was localized on a 709 bp HindIII-HincII fragment. Nucleotide sequence analysis revealed a 213 bp open reading frame whose deduced amino-acid sequence shows a very high homology with that of the Anabaena flos-aquae GVP. Assuming that the first methionine residue is proteolytically processed, the molecular mass of the Calothrix GVP is 7375 daltons. Sequences resembling the Escherichia coli consensus promoter were found upstream from the gvpA gene. The initiator codon of the gvpA gene is preceded by a polypurine sequence assumed to be the ribosome binding site. Southern hybridizations with a probe specific for the gvpA gene indicated that this gene is not plasmid-borne, and that another homologous gene is present in the Calothrix genome.

Amino Acid Sequence↗
PubMed1981

Electron transport to nitrogenase in Klebsiella pneumoniae: purification and properties of the nifJ protein.

In Klebsiella pneumoniae, the physiological electron flow to nitrogenase involves specifically, in addition to nitrogenase reductase, the products of the nifF and nifJ genes. The J protein was purified to homogeneity and was found to be an iron-sulfur protein devoid of molybdenum. In its native state, the J protein is a dimer of Mr about 245 000, made up of two subunits of the same molecular weight. It contains about 30 mol iron and 24 mol labile sulfur/mol protein. The addition of J protein to crude extracts of a nifJ mutant reestablishes pyruvate-supported acetylene-reducing activity. This activity is further enhanced by addition of pure nitrogenase (Kp1). Based on its physical properties, the J protein is probably an oxidoreductase whose physiological role might be to transfer electrons from a metabolic donor to the F protein. In addition, another protein whose activity is also dependent on the nifJ gene seems to be required for the formation of a fully active Kp1.

Bacterial Proteins↗