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J Houmard

Publications and source records attributed to J Houmard.

At least 19 recordsLinked to original sources
PubMed2001

Convergence of two global transcriptional regulators on nitrogen induction of the stress-acclimation gene nblA in the cyanobacterium Synechococcus sp. PCC 7942.

Cyanobacteria respond to environmental stress conditions by degrading their phycobilisomes, the light harvesting complexes for photosynthesis. The expression of nblA, a key gene in this process, is controlled by the response regulator NblR in Synechococcus sp. PCC 7942. Here we show that, under nitrogen stress, nblA is also regulated by NtcA, the global regulator for nitrogen control. NtcA activation of nblA was found to be nitrogen-specific and did not take place under sulphur stress. Transcripts from the two major transcription start points (tsp) for the nblA gene were induced in response to nitrogen and sulphur starvation. The most active one (tspII) required both NblR and NtcA to induce full nblA expression under nitrogen starvation. NblR and NtcA bound in vitro to a DNA fragment from the nblA promoter region, suggesting that, under nitrogen stress, both NblR and NtcA activate the main regulated promoter (PnblA-2) by direct DNA-binding. The structure of PnblA-2 differs from that of the canonical NtcA-activated promoter and it is therefore proposed to represent a novel type of NtcA-dependent promoter. We analysed expression patterns from ntcA and selected NtcA targets in NtcA(-), NblR(-) and wild-type strains, and discuss data suggesting further interrelations between phycobilisome degradation and nitrogen assimilation regulatory pathways.

Bacterial Proteins↗
PubMed2000

A new appraisal of the prokaryotic origin of eukaryotic phytochromes.

The evolutionary origin of the phytochromes of eukaryotes is controversial. Three cyanobacterial proteins have been described as "phytochrome-like" and have been suggested to be potential ancestors of these essential photoreceptors: Cph1 from Synechocystis PCC 6803, showing homology to phytochromes along its entire length and known to attach a chromophore; and PlpA from Synechocystis PCC 6803 and RcaE from Fremyella diplosiphon, both showing homology to phytochromes most strongly only in the C-terminal region and not known to bind a chromophore. We have reexamined the evolution of the photoreceptors using for PCR amplification a highly conserved region encoding the chromophore-binding domain in both Cph1 and phytochromes of plants and have identified genes for phytochrome-like proteins (PLP) in 11 very diverse cyanobacteria. The predicted gene products contain either a Cys, Arg, Ile, or Leu residue at the putative chromophore binding site. In 10 of the strains examined only a single gene was found, but in Calothrix PCC 7601 two genes (cphA and cphB) were identified. Phylogenetic analysis revealed that genes encoding PLP are homologues that share a common ancestor with the phytochromes of eukaryotes and diverged before the latter. In contrast, the putative sensory/regulatory proteins, including PlpA and RcaE, that lack a part of the chromophore lyase domain essential for chromophore attachment on the apophytochrome, are only distantly related to phytochromes. The Ppr protein of the anoxygenic photosynthetic bacterium Rhodospirillum centenum and the bacterial phytochrome-like proteins (BphP) of Deinococcus radiodurans and Pseudomonas aeruginosa fall within the cluster of cyanobacterial phytochromes.

Amino Acid Sequence↗
PubMed2000

Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov. strain PCC 9511, the first axenic chlorophyll a2/b2-containing cyanobacterium (Oxyphotobacteria).

The formal description of Prochlorococcus marinus Chisholm et al. 1992, 299 was based on the non-axenic nomenclatural type, strain CCMP 1375T. The purification and properties of the axenic strain PCC 9511, derived from the same primary culture (SARG) as the type species, are reported here. Prochlorococcus PCC 9511 differs from the latter in possessing horseshoe-shaped thylakoids, exhibiting a low chlorophyll b2 content and lacking phycoerythrin, but shares these phenotypic properties with Prochlorococcus strain CCMP 1378. This relationship was confirmed by 16S rRNA sequence analyses, which clearly demonstrated that the axenic isolate is not co-identic with the nomenclatural type. Strain PCC 9511 has a low mean DNA base composition (32 mol% G+C) and harbours the smallest genome of all known oxyphotobacteria (genome complexity 1.3 GDa = 2 Mbp). Urea and ammonia are the preferred sources of nitrogen for growth, whereas nitrate is not utilized. Several different organic phosphorus compounds efficiently replace phosphate in the culture medium, indicative of ecto-phosphohydrolase activity. In order to distinguish strain PCC 9511 from the nomenclatural type, a new subspecies is proposed, Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov.

Bacterial Typing Techniques↗
PubMed2000

Synechocystis strain PCC 6803 cya2, a prokaryotic gene that encodes a guanylyl cyclase.

Synechocystis strain PCC 6803 exhibits similar levels of cyclic AMP (cAMP) and cyclic GMP (cGMP). A thorough analysis of its genome showed that Cya2 (Sll0646) has all the sequence determinants required in terms of activity and purine specificity for being a guanylyl cyclase. Insertional mutagenesis of cya2 caused a marked reduction in cGMP content without altering the cAMP content. Thus, Cya2 represents the first example of a prokaryotic guanylyl cyclase.

Amino Acid Sequence↗
PubMed1998

Expression of the psbA gene in the marine oxyphotobacteria Prochlorococcus spp.

The oxygenic photosynthetic prokaryotes Prochlorococcus marinus SS120 (CCMP1375) and Prochlorococcus sp. MED4 (CCMP 1378) were previously shown to exhibit different pigmentation and ecophysiological characteristics. The former strain has a much lower divinyl-Chl a to b ratio and is adapted to lower photon flux densities than the latter. In contrast to the cyanobacteria examined so far, both strains possess only one copy of the psbA gene, encoding the D1 protein of photosystem II core. In acclimated steady-state cultures, psbA transcript levels were always higher at high irradiances in both strains. Upon a shift from low to high light, the psbA transcript levels increased in both strains but more quickly in MED4 than in SS120. They decreased during the opposite shift. Iron-starved MED4 cells overexpressed psbA at all assayed irradiances, suggesting that this species, representative of populations from naturally iron-depleted oceanic areas, may have developed a particular compensation mechanism. The similar effects of DCMU and DBMIB on the expression of psbA suggest that light regulation of psbA in Prochlorococcus may be mediated by the electron transport chain. The energy state of cells could, however, also be involved in this regulation, since cultures of both strains subjected to darkness showed psbA levels significantly lower when glucose was added.

Cyanobacteria↗
PubMed1998

A role for the signal transduction protein PII in the control of nitrate/nitrite uptake in a cyanobacterium.

In the cyanobacterium Synechococcus sp. strain PCC 7942, ammonium exerts a rapid and reversible inhibition of the nitrate and nitrite uptake, and the PII protein (GlnB) is differentially phosphorylated depending on the intracellular N/C balance. RNA/DNA hybridizations, as well as nitrate and nitrite uptake experiments, were carried out with the wild-type strain and a PII-null mutant. The transcriptional control by ammonium of the expression of the nir-nrt ABCD-narB operon remained operative in the mutant but, in contrast to the wild-type strain, the mutant took up nitrate and nitrite even in the presence of ammonium. Moreover, the wild-type phenotype was restored by insertion of a copy of the wild-type glnB gene in the genome of the PII-null mutant. These results indicate that the unphosphorylated form of PII is involved in the short-term inhibition by ammonium of the nitrate and nitrite uptake in Synechococcus sp. strain PCC 7942.

Ammonium Chloride↗
PubMed1998

Promoter recognition by a cyanobacterial RNA polymerase: in vitro studies with the Calothrix sp. PCC 7601 transcriptional factors RcaA and RcaD.

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 PlacUV5, but not from wild-type Plac promoters. The different behaviours of the enzymes are discussed in the light of the structural differences that exist between subunits of the RNA polymerases.

Binding Sites↗
PubMed1998

Normal forces and myofibrillar disruption after repeated eccentric exercise.

To investigate the "rapid-adaptation" phenomenon, we examined force, neural, and morphological adaptations in 12 subjects who performed 100 eccentric contractions with the quadriceps muscle (bout 1) and repeated the same exercise after a 2-wk hiatus (bout 2). Two days after bout 1, quadriceps muscle strength and surface electromyographic (EMG) activity declined approximately 37 and 28%, respectively, in the control group (n = 6). At day 2 after bout 1, significant increases occurred in patellar tendon reflex amplitude (approximately 25%), muscle soreness (fivefold), and serum creatine kinase (220%), and 65 +/- 12% of the total number of pixels in the EMG indicated myofibrillar disruption. At day 7 after bout 1, all variables returned to normal. At day 2 after bout 2, no significant changes occurred in force, EMG, creatine kinase, or soreness, but reflex amplitude increased, and 23 +/- 4% of the total number of pixels in the EMG still indicated myofibrillar disruption. The results suggest that the rapid force recovery following eccentric exercise is mediated at least in part by neural factors and that this recovery may occur independently of cell disruption.

Adaptation, Physiological↗
PubMed1997

Prochlorothrix hollandica PCC 9006: genomic properties of an axenic representative of the chlorophyll a/b-containing oxyphotobacteria.

Prochlorothrix hollandica is an oxygenic photosynthetic prokaryote that differs from the cyanobacteria in having chlorophyll a/b-protein complexes instead of phycobilisomes as major light-harvesting antennae. We report the isolation and culturing of an axenic strain of P. hollandica, available from the Pasteur Culture Collection of Cyanobacteria as strain PCC 9006. The strain has a mean DNA base composition of 51.6 +/- 0.1 mol% G+C and a genomic complexity of 3.37 +/- 0.17 x 10(9) daltons (5,505 kb). A reiterated DNA sequence represents approximately 4.4% of the genome. Restriction enzyme isoschizomers with different sensitivities to base methylation were used to demonstrate that most A residues in the sequence GATC are methylated in P. hollandica DNA and that this methylation increases with culture age. Furthermore, some C residues are methylated, although the specificity of the C methylation system does not match that of well-characterized C methylases. Nucleotide analysis showed that up to approximately 3.5% of both dA and dC residues are methylated in P. hollandica DNA.

Base Pairing↗
PubMed1997

A role for cpeYZ in cyanobacterial phycoerythrin biosynthesis.

Pigment mutant strain FdR1 of the filamentous cyanobacterium Fremyella diplosiphon is characterized by constitutive synthesis of the phycobiliprotein phycoerythrin due to insertional inactivation of the rcaC regulatory gene by endogenous transposon Tn5469. Whereas the parental strain Fd33 harbors five genomic copies of Tn5469, cells of strain FdR1 harbor six genomic copies of the element; the sixth copy in FdR1 is localized to the rcaC gene. Electroporation of FdR1 cells yielded secondary pigment mutant strains FdR1E1 and FdR1E4, which identically exhibited the FdR1 phenotype with significantly reduced levels of phycoerythrin. In both FdR1E1 and FdR1E4, a seventh genomic copy of Tn5469 was localized to the cpeY gene of the sequenced but phenotypically uncharacterized cpeYZ gene set. This gene set is located downstream of the cpeBA operon which encodes the alpha and beta subunits of phycoerythrin. Complementation experiments correlated cpeYZ activity to the phenotype of strains FdR1E1 and FdR1E4. The predicted CpeY and CpeZ proteins share significant sequence identity with the products of homologous cpeY and cpeZ genes reported for Pseudanabaena sp. strain PCC 7409 and Synechococcus sp. strain WH 8020, both of which synthesize phycoerythrin. The CpeY and CpeZ proteins belong to a family of structurally related cyanobacterial proteins that includes the subunits of the CpcE/CpcF phycocyanin alpha-subunit lyase of Synechococcus sp. strain PCC 7002 and the subunits of the PecE/PecF phycoerythrocyanin alpha-subunit lyase of Anabaena sp. strain PCC 7120. Phycobilisomes isolated from mutant strains FdR1E1 and FdR1E4 contained equal amounts of chromophorylated alpha and beta subunits of phycoerythrin at 46% of the levels of the parental strain FdR1. These results suggest that the cpeYZ gene products function in phycoerythrin synthesis, possibly as a lyase involved in the attachment of phycoerythrobilin to the alpha or beta subunit.

Amino Acid Sequence↗
PubMed1994

A phosphorylated DNA-binding protein is specific for the red-light signal during complementary chromatic adaptation in cyanobacteria.

Complementary chromatic adaptation is a mechanism by which some cyanobacteria that are able to synthesize phycoerythrin can adapt their pigment (phycobiliprotein) content to the incident wavelengths of the light. In Calothrix sp. PCC 7601 it concerns phycoerythrin (cpe operon), synthesized under green light, and phycocyanin-2 (cpc2 operon), expressed under red light, and involves transcriptional controls. With cell-free extracts from Calothrix sp. PCC 7601 grown under various light regimes, a protein designated RcaD was found by gel retardation experiments to specifically bind to the cpc2 promoter region and to be present only in red-light-grown cells. This protein was partially purified and its binding activity was shown to be sensitive to an alkaline phosphatase treatment. RcaD can protect two regions of the cpc2 promoter sequence against degradation by DNase I. Because its activity is detected only under the conditions required for cpc2 expression, we propose that RcaD is a positive effector of transcription.

Adaptation, Physiological↗
PubMed1994

Specific initiation of transcription at a cyanobacterial promoter with RNA polymerase purified from Calothrix sp. PCC 7601.

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.

Bacterial Proteins↗
PubMed1993

An in vivo approach to define the role of the LCM, the key polypeptide of cyanobacterial phycobilisomes.

In cyanobacteria, phycobilisomes are regularly arrayed on the surface of the photosynthetic membranes, and their role is to funnel light energy to the underlying photosystem II reaction center. A model has recently been proposed that ascribes to the so-called LCM, a central role in the building up of the phycobilisome, in addition to its role of terminal energy acceptor (Capuano, V., Braux, A.-S., Tandeau de Marsac, N., and Houmard, J. (1991) J. Biol. Chem. 266, 7239-7247). The phycobilisomes of Calothrix sp. PCC 7601 are typically of the type found in most cyanobacteria. Those of Synechococcus PCC 7942 (or PCC 6301) differ in having central cores made up of two instead of three cylinders. We have integrated the Calothrix PCC 7601 apcE gene that encodes the LCM into the chromosome of a Synechococcus PCC 7942 strain. We have observed that the heterologous gene is expressed and that the corresponding product carries a bilin-type chromophore and can be detected in the phycobilisome fraction of the Synechococcus strain. Moreover, it is shown that, in agreement with our model, this LCM can direct the formation of phycobilisomes that have three-cylinder cores.

Bacterial Proteins↗
PubMed1993

Transduction of the light signal during complementary chromatic adaptation in the cyanobacterium Calothrix sp. PCC 7601: DNA-binding proteins and modulation by phosphorylation.

The cyanobacterium Calothrix sp. PCC 7601 can adapt its pigment content in response to changes in the incident light wavelength. It synthesizes, as major light-harvesting pigments, either phycocyanin 2 (PC2, encoded by the cpc2 operon) under red light or phycoerythrin (PE, encoded by the cpeBA operon) under green light conditions. The last step of the signal transduction pathway is characterized by a transcriptional control of the expression of these operons. Partially purified protein extracts were used in gel retardation assays and DNase I footprinting experiments to identify the factors that interact with the promoter region of the cpeBA operon. We found that two proteins, RcaA and RcaB, only detected in extracts of cells grown under green light, behave as positive transcriptional factors for the expression of the cpeBA operon. Treatment of the fractions containing RcaA and RcaB with alkaline phosphatase prevents the binding of RcaA but not of RcaB to the cpeBA promoter region. A post-translational modification of RcaA thus modulates its affinity for DNA.

Adaptation, Physiological↗
PubMed1993

Muscle hypertrophy with large-scale weight loss and resistance training.

The combined effects of exercise and energy restriction on changes in body fat and fat-free mass (FFM) are controversial. This study was conducted to determine whether muscle hypertrophy is possible during weight loss. Fourteen obese females received a 3360-kJ/d liquid diet for 90 d. Seven subjects received a weight training (WT) regimen and seven subjects remained sedentary (C). Biopsy samples were obtained from the vastus lateralis muscle at baseline and after 90 d of treatment. The average weight loss over the 90-d period was 16 kg with approximately 24% of the weight loss from FFM and 76% from fat. The amount and composition of the weight loss did not differ between WT and C groups. The cross-sectional area of slow twitch and fast twitch fibers was unchanged by treatment in C subjects but significantly increased in WT subjects. It appears that weight training can produce hypertrophy in skeletal muscle during severe energy restriction and large-scale weight loss.

Adult↗
PubMed1992

Molecular characterization of the gene encoding glutamine synthetase in the cyanobacterium Calothrix sp. PCC 7601.

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.

Amino Acid Sequence↗
PubMed1991

The "anchor polypeptide" of cyanobacterial phycobilisomes. Molecular characterization of the Synechococcus sp. PCC 6301 apce gene.

In cyanobacteria, light energy is mainly harvested by the phycobiliproteins that form the phycobilisome rods, and funneled to the photosynthetic reaction centers through the core components. Among them, allophycocyanin (alpha AP, beta AP) and the so-called LCM play a major role. This report deals with the characterization of the apcE gene from Synechococcus sp. PCC 6301 which specifies the LCM. It maps upstream from the apcA gene (alpha AP). Transcriptional analyses demonstrate that the apcABC gene cluster (alpha AP, beta AP, and LC7.8) forms an operon, whereas the apcE gene behaves as a monocistronic unit. The functional organization of the apcEABC gene cluster, as well as of the apcE gene product, of Synechococcus 6301 are compared to their counterparts in three other organisms. Finally, a model is proposed for the architecture of the phycobilisome core.

Amino Acid Sequence↗