Showing papers by "Centre national de la recherche scientifique published in 1990"

The monadic second-order logic of graphs. I. recognizable sets of finite graphs

Abstract: The notion of a recognizable set of finite graphs is introduced. Every set of finite graphs, that is definable in monadic second-order logic is recognizable, but not vice versa. The monadic second-order theory of a context-free set of graphs is decidable.

Two distinct estrogen‐regulated promoters generate transcripts encoding the two functionally different human progesterone receptor forms A and B.

Abstract: The human progesterone receptor (hPR) cDNA, synthesized from T47D breast cancer cells, and the hPR gene 5'-flanking region were cloned and sequenced. Comparison of the cDNA-deduced amino acid sequence with other PR homologues demonstrated the modular structure characteristic of nuclear receptors. As in the case of the chicken homologue, there are two hPR forms, A and B, which originate from translational initiation at AUG2 (codon 165) and AUG1, respectively. Northern blot analysis of T47D mRNA using various cDNA derived probes identified two classes of hPR mRNAs, one of which could code for hPR form B, while the other one lacked the 5' region upstream of AUG1. S1 nuclease mapping and primer extension analyses confirmed that the second class of hPR transcripts are initiated between +737 and +842 and thus encode hPR form A, but not form B. By using the hPR gene 5'-flanking sequences as promoter region in chimeric genes, we show that a functional promoter (located between -711 and +31) directs initiation of hPR mRNAs from the authentic start sites located at +1 and +15. Most importantly, initiation of transcription from chimeric genes demonstrated the existence of a second promoter located between +464 and +1105. Transient co-transfection experiments with vectors expressing the human estrogen receptor showed that both promoters were estrogen inducible, although no classical estrogen responsive element was detected in the corresponding sequences. When transiently expressed, the two hPR forms similarly activated transcription from reporter genes containing a single palindromic progestin responsive element (PRE), while form B was more efficient at activating the PRE of the mouse mammary tumor virus long terminal repeat. Transcription from the ovalbumin promoter, however, was induced by hPR form A, but not by form B.

Calibration of the C-14 timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals

Abstract: Uranium-thorium ages obtained by mass spectrometry from corals raised off the island of Barbados confirm the high precision of this technique over at least the past 30,000 years. Comparison of the U-Th ages with C-14 ages obtained on the Holocene samples shows that the U-Th ages are accurate, because they accord with the dendrochronological calibration. Before 9,000 yr BP, the C-14 ages are systematically younger than the U-Th ages, with a maximum difference of about 3500 yr at about 20,000 yr BP. The U-Th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration.

Superconductivity in narrow-band systems with local nonretarded attractive interactions

Abstract: In narrow-band systems electrons can interact with each other via a short-range nonretarded attractive potential. The origin of such an effective local attraction can be polaronic or it can be due to a coupling between electrons and excitons or plasmons. It can also result from purely chemical (electronic) mechanisms, especially in compounds with elements favoring disproportionation of valent states. These mechanisms are discussed and an exhaustive list of materials in which such local electron pairing occurs is given. The authors review the thermodynamic and electromagnetic properties of such systems in several limiting scenarios: (i) Systems with on-site pairing which can be described by the extended negative-$U$ Hubbard model. The strong-attraction limit of this model, at which it reduces to a system of tightly bound electron pairs (bipolarons) on a lattice, is extensively discussed. These electron pairs behaving as hard-core charged bosons can exhibit a superconducting state analogous to that of superfluid $^{4}\mathrm{He}$ II. The change-over from weak-attraction BCS-like superconductivity to the superfluidity of charged hard-core bosons is examined. (ii) Systems with intersite pairing described by an extended Hubbard model with $Ug0$ and nearest-neighbor attraction and/or nearest-neighbor spin exchange as well as correlated hopping. (iii) A mixture of local pairs and itinerant electrons interacting via a charge-exchange mechanism giving rise to a mutually induced superconductivity in both subsystems. The authors discuss to what extent the picture of local pairing, and in particular superfluidity of hard-core charged bosons on a lattice, can be an explanation for the superconducting and normal-state properties of the high-${T}_{c}$ oxides: doped BaBi${\mathrm{O}}_{3}$ and the cuprates.

Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs

Abstract: The aminoacyl-transfer RNA synthetases (aaRS) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology. Out of the 18 known aaRS, only 9 referred to as class I synthetases (GlnRS, TyrRS, MetRS, GluRS, ArgRS, ValRS, IleRS, LeuRS, TrpRS), display two short common consensus sequences ('HIGH' and 'KMSKS') which indicate, as observed in three crystal structures, the presence of a structural domain (the Rossman fold) that binds ATP. We report here the sequence of Escherichia coli ProRS, a dimer of relative molecular mass 127,402, which is homologous to both ThrRS and SerRS. These three latter aaRS share three new sequence motifs with AspRS, AsnRS, LysRS, HisRS and the beta subunit of PheRS. These three motifs (motifs 1, 2 and 3), in a search through the entire data bank, proved to be specific for this set of aaRS (referred to as class II). Class II may also contain AlaRS and GlyRS, because these sequences have a typical motif 3. Surprisingly, this partition of aaRS in two classes is found to be strongly correlated on the functional level with the acylation occurring either on the 2' OH (class I) or 3' OH (class II) of the ribose of the last nucleotide of tRNA.

A novel metalloproteinase gene specifically expressed in stromal cells of breast carcinomas

Abstract: A gene has been identified that is expressed specifically in stromal cells surrounding invasive breast carcinomas. On the basis of its sequence, the product of this gene, named stromelysin-3, is a new member of the family of metalloproteinase enzymes which degrade the extracellular matrix. The suggestion is that stromelysin-3 is one of the stroma-derived factors that have long been postulated to play an important part in progression of epithelial malignancies.

Symbiotic host-specificity of Rhizobium meliloti is determined by a sulphated and acylated glucosamine oligosaccharide signal.

Abstract: Rhizobia are symbiotic bacteria that elicit the formation on leguminous plants of specialized organs, root nodules, in which they fix nitrogen. In various Rhizobium species, such as R. leguminosarum and R. meliloti, common and host-specific nodulation (nod) genes have been identified which determine infection and nodulation of specific hosts. Common nodABC genes as well as host-specific nodH and nodQ genes were shown recently, using bioassays, to be involved in the production of extracellular Nod signals. Using R. meliloti strains overproducing symbiotic Nod factors, we have purified the major alfalfa-specific signal, NodRm-1, by gel permeation, ion exchange and C18 reverse-phase high performance liquid chromatography. From mass spectrometry, nuclear magnetic resonance, (35)S-labelling and chemical modification studies, NodRm-1 was shown to be a sulphated beta-1,4-tetrasaccharide of D-glucosamine (Mr 1,102) in which three amino groups were acetylated and one was acylated with a C16 bis-unsaturated fatty acid. This purified Nod signal specifically elicited root hair deformation on the homologous host when added in nanomolar concentration.

Single pentacene molecules detected by fluorescence excitation in a p-terphenyl crystal.

Abstract: Experiments clearly prove that narrow peaks in the fluorescence-excitation spectrum of a pentacene-doped p-terphenyl crystal stem from single molecules. This claim is supported by the distribution, width, and height of the peaks, as well as by the correlation of the emitted light and the sudden drops and surges of the emission of certain peaks. We attribute these to the hole burning of a single molecule. These results show the feasibility of the optical study of a single molecule and its local environment.

Structural anomalies, oxygen ordering and superconductivity in oxygen deficient Ba2YCu3Ox

Abstract: We report the characterization of series of oxygen deficient Ba2YCu3Ox samples for 7 ≥ x ≥ 6 prepared by Zr gettered annealing at 440°C. Measurements include complete crystal structure analysis at 5 K by powder neutron diffraction, electron microscopy study of the oxygen ordering, and magnetic measurements of the superconducting transitions, with particular attention to the transition widths. The results show for the first time that the 90 K and 60 K plateaus in Tc as a function of oxygen stoichiometry are associated with plateaus in the effective valence of the plane coppers. We also correlate the disappearance of superconductivity for x

U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years

Abstract: THE study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep-sea sediments1,2. The direct approach of dating sea level indicators stagnated during the past decade, mainly because the samples required to complete our knowledge of the past glaciations are below the present-day sea level3–7. Using the 14C ages of Acropora palmata samples collected by drilling offshore the island of Barbados, Fairbanks8 presented the first detailed chronology for the last deglaciation. This radiocarbon chronology is limited to the past 30 kyr because of the short half-life of 14C (5,730 yr); we must therefore rely on other dating methods to obtain information for the whole last glacial cycle. During the past four years 230Th–234U dating of corals by thermal-ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical α counting method9–14. We have used this technique to measure U–Th ages in coral samples from the Barbados collection and from subaerially exposed outcrops (see also ref. 15). Here we present results bearing on the sea level record for the past 130,000 years; we conclude that the last deglaciation started 3,000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr BP (before present).

Role of the two activating domains of the oestrogen receptor in the cell-type and promoter-context dependent agonistic activity of the anti-oestrogen 4-hydroxytamoxifen.

Abstract: Various oestrogen responsive reporter genes and vectors expressing truncated or chimeric human oestrogen receptors (hER) containing either of the two independent hER transcriptional activation functions (TAF-1 and TAF-2) have been transfected into HeLa cells, chicken embryo fibroblast (CEF) or yeast cells to investigate the agonistic activity of the anti-oestrogen 4-hydroxytamoxifen (OHT). We demonstrate that the agonistic effect of OHT on the whole hER is due to the cell-type and promoter-context dependent activity of TAF-1. In similar experiments, we show that the anti-oestrogen, ICI 164,384, does not exhibit any oestrogenic activity and, therefore, acts always as a pure antagonist, even though it does not inhibit the activity of the isolated TAF-1. We also confirm that the wild type human oestrogen receptor has no ligand independent transcriptional activity. The implications of our results for the variable antagonist/agonist activity of anti-oestrogens in vivo are discussed.

How to draw a planar graph on a grid

Abstract: Answering a question of Rosenstiehl and Tarjan, we show that every plane graph withn vertices has a Fary embedding (i.e., straight-line embedding) on the 2n−4 byn−2 grid and provide anO(n) space,O(n logn) time algorithm to effect this embedding. The grid size is asymptotically optimal and it had been previously unknown whether one can always find a polynomial sized grid to support such an embedding. On the other hand we show that any setF, which can support a Fary embedding of every planar graph of sizen, has cardinality at leastn+(1−o(1))√n which settles a problem of Mohar.

Head stabilization during various locomotor tasks in humans. I. Normal subjects.

Abstract: Head kinematics were studied in ten normal subjects while they executed various locomotor tasks The movement of the body was recorded with a video system which allowed a computer reconstruction of motion of joint articulations and other selected points on the body in three dimensions Analyses focus on head translation along the vertical axis and rotation in the sagittal plane This was done by recording the displacement of a line approximating the plane of horizontal semi-circular canals (the Frankfort plane: F-P) Four conditions were studied: free walking (W) walking in place (WIP) running in place (R) and hopping (H) In the 4 experimental conditions, amplitude and velocity of head translation along the vertical axis ranged from 1 cm to 25 cm and 015 m/s to 18 m/s In spite of the disparities in the tasks regarding the magnitude of dynamic components, we found a significant stabilization of the F-P around the earth horizontal Maximum amplitude of F-P rotation did not exceed 20° in the 4 situations Vertical angular velocities increased from locomotion tasks to the dynamic equilibrium task although the maximum values remained less than 140°/s Predominant frequencies of translations and rotations in all the tasks were within the range 04–35 Hz and harmonics were present up to 6–8 Hz During walking in darkness, mean head position is tilted downward, with the F-P always below the earth horizontal Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, WIP and R, but during H the amplitude decreased by 37% Residual head angular displacement is found to compensate for head translation during the 4 conditions Our study emphasizes the importance of head stabilization as part of the postural control system and described as a basis for inertial guidance

An attempt to unify the structure of polymerases

Abstract: With the great availability of sequences from RNA- and DNAdependent RNA and DNA polymerases, it has become possible to delineate a few highly conserved regions for various polymerase types. In this work a DNA polymerase sequence from bacteriophage SPO2 was found to be homologous to the polymerase domain of the Klenow fragment of polymerase I from Escherichia coli, which is known to be closely related to those from Staphylococcus pneumoniae, Thermits aquaticus and bacteriophages T7 and T5. The alignment of the SPO2 polymerase with the other five sequences considerably narrowed the conserved motifs in these proteins. Three of the motifs matched reasonably all the conserved motifs of another DNA polymerase type, characterized by human polymerase a. It is also possible to find these three motifs in monomeric DNA-dependent RNA polymerases and two of them in DNA polymerase /3 and DNA terminal transferases. These latter two motifs also matched two of the four motifs recently identified in 84 RNA-dependent polymerases. From the known tertiary architecture of the Klenow fragment of E.coli pol I, a spatial arrangement can be implied for these motifs. In addition, numerous biochemical experiments suggesting a role for the motifs in a common function (dNTP binding) also support these inferences. This speculative hypothesis, attempting to unify polymerase structure at least locally, if not globally, under the pol I fold, should provide a useful model to direct mutagenesis experiments to probe template and substrate specificity in polymerases.

Fault injection for dependability validation: a methodology and some applications

Abstract: The authors address the problem of validating the dependability of fault-tolerant computing systems, in particular, the validation of the fault-tolerance mechanisms. The proposed approach is based on the use of fault injection at the physical level on a hardware/software prototype of the system considered. The place of this approach in a validation-directed design process and with respect to related work on fault injection is clearly identified. The major requirements and problems related to the development and application of a validation methodology based on fault injection are presented and discussed. Emphasis is put on the definition, analysis, and use of the experimental dependability measures that can be obtained. The proposed methodology has been implemented through the realization of a general pin-level fault injection tool (MESSALINE), and its usefulness is demonstrated by the application of MESSALINE to the experimental validation of two systems: a subsystem of a centralized computerized interlocking system for railway control applications and a distributed system corresponding to the current implementation of the dependable communication system of the ESPRIT Delta-4 Project. >

Retinoic acid receptors and cellular retinoid binding proteins. I. A systematic study of their differential pattern of transcription during mouse organogenesis.

Abstract: We report here the gene expression patterns, as revealed by in situ hybridisation, of the retinoic acid receptors alpha, beta and gamma (RAR-alpha, -beta and -gamma), and the cellular binding proteins for retinol and retinoic acid (CRBP, CRABP) in non-neural tissues of mouse embryos during the period of organogenesis. At all stages, RAR-alpha transcripts were almost ubiquitous, whereas the distribution of transcripts of the other four genes was distinctive in all systems. At early stages in the formation of an organ, the expression patterns were different in the epithelium, the adjacent mesenchyme, and in mesenchyme more distant from the epithelium, suggesting a role for RA and RA receptors in epithelial-mesenchymal tissue interactions. In the developing face, limb bud and genital tubercle, where large expanses of mesenchyme are present, differential patterns of expression were established before the onset of overt tissue differentiation, suggesting some significance for pattern formation in these regions. The distribution of RAR-beta transcripts in tracheobronchial, intestinal and genital tract epithelial is consistent with the possibility that RAR-beta plays a role in mediating retinoid effects on the differentiated stage of these epithelia. Possible developmental roles of RARs in relation to the expression patterns of other genes are discussed. CRBP expression domains showed a high degree of overlap with RAR-beta and RAR-gamma, and a mutual exclusivity with CRABP expression domains. Correlation of these expression patterns with the morphogenetic effects of vitamin A deficiency and retinoid excess lead us to propose that the function of CRBP is to store and release retinol where high levels of RA are required for specific morphogenetic processes, while CRABP serves to sequester RA in regions where normal developmental functions require RA levels to be low. Where both binding protein genes are expressed in a non-overlapping pattern within a large area of mesenchyme, a gradient of free RA may be created between them by release of retinol-derived RA from CRBP-expressing cells, with binding to CRABP enhancing the steepness of the decline in concentration distant to the source.

Increases in terrestrial carbon storage from the last glacial maximum to the present

Abstract: EVIDENCE from ice cores1 indicates that concentrations of atmospheric carbon dioxide were lower by about 75 p.p.m. during the Last Glacial Maximum (LGM; ∼18,000 years ago) than during the present interglacial (10,000 years ago to the present). The causes of such large changes in atmospheric CO2 remain uncertain. Using a climate model, Prentice and Fung2 have estimated that there was approximately the same amount of carbon in vegetation and soils during the LGM as there was during the present (pre-industrial) interglacial. In contrast, we present here results based on palynological, pedological and sedimentological evidence which indicate that in fact the amount of carbon in vegetation, soils and peatlands may have been smaller during the LGM by ∼1.3x 1012 tonnes. Thus, organic carbon in vegetation and soils has more than doubled (from 0.96 to 2.3 x 1012 tonnes) since the LGM. Oceanic CO2 reservoirs seem to be the only possible source of this large quantity of carbon that has entered the terrestrial biosphere since the LGM (in addition to that which has entered the atmosphere to give the higher interglacial CO2 levels).

The construction of the L3 experiment

Abstract: The L3 experiment is one of the six large detectors designed for the new generation of electron-positron accelerators. It is the only detector that concentrates its efforts on limited goals of measuring electrons, muons and photons. By not attempting to identify hadrons, L3 has been able to provide an order of magnitude better resolution for electrons, muons and photons. Vertices and hadron jets are also studied. The construction of L3 has involved much state of the art technology in new principles of vertex detection and in new crystals for large scale electromagnetic shower detection and ultraprecise muon detection. This paper presents a summary of the construction of L3.

Characterization of a Mycobacterium tuberculosis insertion sequence, IS6110, and its application in diagnosis.

Abstract: An insertion sequence-like element, IS6110, was isolated from a Mycobacterium tuberculosis cosmid library as a repetitive sequence. IS6110 shows similarities with elements of the IS3 family. This insertion sequence was found to be specific to mycobacteria belonging to the M. tuberculosis complex. For detection and identification of M. tuberculosis bacilli in uncultured specimens, oligonucleotides derived from the IS6110 sequence were used as primers and probes in polymerase chain reaction studies. The results obtained were consistent with results of classical identification procedures, bacteriological data, and clinical criteria.

Posttranslational glutamylation of alpha-tubulin

Abstract: The high degree of tubulin heterogeneity in neurons is controlled mainly at the posttranslational level. Several variants of alpha-tubulin can be posttranslationally labeled after incubation of cells with [3H]acetate or [3H]glutamate. Peptides carrying the radioactive moiety were purified by high-performance liquid chromatography. Amino acid analysis, Edman degradation sequencing, and mass spectrometric analysis of these peptides led to the characterization of a posttranslational modification consisting of the successive addition of glutamyl units on the gamma-carboxyl group of a glutamate residue (Glu445). This modification, localized within a region of alpha-tubulin that is important in the interactions of tubulin with microtubule-associated proteins and calcium, could play a role in regulating microtubule dynamics.

Satellite tracking of Wandering albatrosses

Abstract: ALTHOUGH the study of seabirds in their land-based breeding colonies has attracted much attention, an understanding of their ecology at sea, particularly their foraging range and the location of their feeding zones, remains a major challenge1. The foraging range of pelagic feeders nesting on a given colony or island is purely speculative2,3. Since the eighteenth century4, the Wandering albatross (Diomedea exulans) has been thought to be one of the most widely ranging seabirds, and breeders are thought to travel up to 1,800 km from the nest on foraging trips5,6. Here, we describe the first successful tracking of a bird using satellite telemetry. Tracks of Wandering albatrosses in the southwestern Indian Ocean showed that they covered between 3,600 and 15,000 km in a single foraging trip during an incubation shift. They flew at speeds of up to 80 km per h and over distances of up to 900 km per day. They remained active at night, particularly on moonlit nights and wind appeared to have a major influence on the foraging strategy of these albatrosses. Detailed knowledge of their movements at sea may prove critical to the conservation of the Wandering albatross and particularly of the closely related Amsterdam albatross (D. amsterdamensis), both of which are endangered7–9.