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We study the effect of Coulomb correlations on the ultrafast optical dynamics of small metal particles. We demonstrate that a surface-induced dynamical screening of the electron-electron interactions leads to quasiparticle scattering with collective surface excitations. In noble-metal nanoparticles, it results in an interband resonant scattering of d-holes with surface plasmons. We show that this size-dependent many-body effect manifests itself in the differential absorption dynamics for frequencies close to the surface plasmon resonance. In particular, our self-consistent calculations reveal a strong frequency dependence of the relaxation, in agreement with recent femtosecond pump-probe experiments., 8 pages + 4 figures, final version accepted to PRL

The dynamics of electrons heated with femtosecond optical pulses is investigated in silver nanoparticles. The electron-lattice relaxation is compared for particles in various surrounding matrixes.

The Diadromus pulchellus ascovirus (DpAV) has been isolated from laboratory strains of Diadromus pulchellus and in natural wild populations collected from the Antibes locality (southern France). The DpAV genome was found in the cells of the head, thorax and abdomen of this hymenopteran wasp. DpAV virions are present in the female genitalia and are transmitted to the nymphal lepidopteran host, Acrolepiopsis assectella, at each oviposition of the female wasp. The presence of the DpAV genome in all Diadromus somatic cells suggests that it is inherited by vertical transmission. DpAV is amplified in the host tissues during the larval development of D. pulchellus in A. assectella. Cell lysis due to amplification of the virus does not prevent the development of the hymenopteran larva. Virus amplification appears to be slower in nymphs parasitized by D. pulchellus than in nymphs artificially infected with DpAV alone. Lysis of the nymphal cells due to viral replication seems to be synchronous with egg hatching and the development of the hymenopteran larva. The features of DpAV and its relationship with the parasitoid wasp D. pulchellus during its development are compared to those of the ichnoviruses.

The present report describes the use of computer analyses to reveal a hobo -like element in the genome of Caenorhabditis elegans . This hobo -like sequence is 3039 bp long, contains two inverted terminal repeats of 25–27 bp and probably does not encoded a functional transposase. Sequence comparisons suggest that each transposase of hobo elements probably has a D(D/S)E motif. Thus the transposases of the hAT superfamily of transposons appear to be close to the other transposases and intregrases.

In order to make a comparison between the properties of low molecular weight poly(phenyleneethynylene) type compounds and the corresponding high molecular weight polymers, we have synthesized oligomers and model molecules of poly(phenyleneethynylene) derivatives by two different routes. This paper describes the synthesis and the X-ray and optical characterization of conjugated soluble oligomers, as well as model trimers and pentamers of the same structure in which the solubility was improved by fixing flexible alkyl chains of 10 or 12 carbons to the backbone. The electron density on the phenyl ring was also enhanced or reduced by introducing either electron-donor or electron-acceptor groups. The oligomers were synthesized by polycondensation using a palladium catalyzed coupling reaction, between a bromoaryl and an ethynylaryl unit, with HBr elimination. This method allows the insertion of a triple bond between two phenyl groups. It was initially used in our laboratory in order to obtain high molecular weight polymers. It has been adapted to favor the production of lower molecular weight compounds, by shortening the reaction time or by an important increase of the amount of catalyst. The trimers and pentamers were synthesized step by step by using a route which involves a selective protection-deprotection method, followed by the palladium coupling reaction. Model compounds and oligomers were characterized by UV-visible and Raman spectroscopies, as well as nonlinear optical measurements of the third order susceptibilities (chi((3))) These measurements allowed us to show the influence of the donor/acceptor groups and the chain lengths on the absorption wavelength. In addition, the nonlinear optical measurements show that the chi((3)) value of the pentamer (1.6 x 10(-10) esu) is close to the value of the polymer (4.6 x 10(-10) esu).

The spin dynamics in nickel films is studied with femtosecond magneto-optical pump-probe techniques. The onset of an ultrafast demagnetization is observed as the spin temperature, induced by femtosecond optical pulses, raises close to the Curie point T C .

The dynamics of th wavepacket associated to the high frequency C=C molecular motion (23 fs period) of a polydiacetylene backbone is reported.

The ultrafast dynamics of poly[1.6‐di(n‐carbazolyl‐2.4hexadiyne] (pDCH) has been investigated with femtosecond optical pulses. A transient configuration change of the pDCH backbone occurs in the first 50 fs leading to a butatrienic‐like structure in the excited state. This process is followed by a thermalization of free excitons in the coordinate space with a time constant ∼150 fs.

Copies of mariner-like element (MLE) transposons in two species, the bumble bee, Bombus terrestris, and the ant, Myrmica ruginodis, were sequenced. The full-sized elements are 1250 bp long in both species and include 28-bp inverted terminal repeats. The five copies sequenced were approximately 75% similar to a mariner element (peach) of Drosophila mauritiana. The distribution of MLE in 27 hymenopteran species was studied by PCR and Southern blot hybridization; 93% of the species contained one or more of the four major forms of the element. They are inserted in their host genomes, in the middle of a degenerated 30-bp palindrome, which is itself located in an 85-bp conserved region with a purine-rich tail at one of its ends. The hymenopteran MLEs lie in a specific insertion site, suggesting that this region is conserved. It is thus possible that this region may be a selectively neutral insertion site, which would explain why these elements are widespread in hymenopteran genomes and are not eliminated by male haploidy.

Coherent light scattering is an ideal tool to investigate the microscopic interactions that take place in various diluted or condensed phase systems1. It is of particular interest in semiconductors where the Coulomb interaction between electrons and holes brings new features in the dynamics of the polarization established by ultrashort optical pulses2. Due to this Coulomb coupling the coherent emission observed in different wave-mixing geometries behaves in a non-trivial fashion. The usual description of the material relaxation with a simple transverse time T 2, as is done for atomic-like systems3, is no longer sufficient. Although the underlying physics is more complex, one may picture these different regimes by analogy with oscillators: the exponential T 2 behavior corresponds to a damped harmonic oscillator, while the Coulomb interacting system leads to a non-exponential damping, as with nonlinear coupled oscillators.

Background Female endoparasitic ichneumonid wasps inject virus-like particles into their caterpillar hosts to suppress immunity. These particles are classified as ichnovirus virions and resemble ascovirus virions, which are also transmitted by parasitic wasps and attack caterpillars. Ascoviruses replicate DNA and produce virions. Polydnavirus DNA consists of wasp DNA replicated by the wasp from its genome, which also directs particle synthesis. Structural similarities between ascovirus and ichnovirus particles and the biology of their transmission suggest that ichnoviruses evolved from ascoviruses, although molecular evidence for this hypothesis is lacking. Results Here we show that a family of unique pox-D5 NTPase proteins in the Glypta fumiferanae ichnovirus are related to three Diadromus pulchellus ascovirus proteins encoded by ORFs 90, 91 and 93. A new alignment technique also shows that two proteins from a related ichnovirus are orthologs of other ascovirus virion proteins. Conclusion Our results provide molecular evidence supporting the origin of ichnoviruses from ascoviruses by lateral transfer of ascoviral genes into ichneumonid wasp genomes, perhaps the first example of symbiogenesis between large DNA viruses and eukaryotic organisms. We also discuss the limits of this evidence through complementary studies, which revealed that passive lateral transfer of viral genes among polydnaviral, bacterial, and wasp genomes may have occurred repeatedly through an intimate coupling of both recombination and replication of viral genomes during evolution. The impact of passive lateral transfers on evolutionary relationships between polydnaviruses and viruses with large double-stranded genomes is considered in the context of the theory of symbiogenesis.

Using femtosecond optical spectroscopy, we study the ultrafast dynamics of the surface plasmon polaritons in gold arrays of subwavelength holes. A large time dependent spectral broadening and shift of the surface plasmon resonances are reported. The experimental results are modeled by the diffraction of a transverse electromagnetic field through the nanostructure, taking into account both the electron dynamics near the interband transitions and the Drude-like conductivity of the metal. Our analysis, using either a theoretical or an experimentally determined dielectric function of gold, suggests that the losses propagation in plasmonic devices is strongly influenced by intrinsic and extrinsic electron scattering mechanisms.

Background Mariner-like elements (MLEs) are widespread DNA transposons in animal genomes. Although in vitro transposition reactions require only the transposase, various factors depending on the host, the physico-chemical environment and the transposon sequence can interfere with the MLEs transposition in vivo. Results The transposition of Mos1, first isolated from drosophila mauritiana, depends of both the nucleic acid sequence of the DNA stuffer (in terms of GC content), and its length. We provide the first in vitro experimental demonstration that MITEs of MLE origin, as small as 80 to 120-bp, are able to transpose. Excessive temperature down-regulates Mos1 transposition, yielding excision products unable to re-integrate. Finally, the super-helicity of the DNA transposon donor has a dramatic impact on the transposition efficiency. Conclusion The study highlights how experimental conditions can bias interpretation of mariner excision frequency and quality. In vitro, the auto-integration pathway markedly limits transposition efficiency to new target sites, and this phenomenon may also limit events in the natural host. We propose a model for small transposons transposition that bypasses DNA bending constraints.

Large quantities of satellite DNA families ( 15%25% of the genome) were found in the DNA of two species of parasitic wasps, Diadromus pulchellus and Eupelmus vuilleti. In both species the satellite DNA was found to consist wholly or largely of a single family unique to that species. Several clones of each family were obtained and sequenced. Palindromes in each consensus sequence suggest the formation in vivo of hairpin structures that may play a role in the mode of heterochromatin condensation in these insects. The ancestral repeating motifs were determined from the consensus sequences. Plausible scenarios are presented for the evolution of the two satellite DNAs. The occurrence of only one family of satellite DNAs in both species may indicate that, in male haploids, such families have shorter persistence times than necessary for the origins of new duplicated sequences.

The ultrafast magnetization dynamics induced in ferromagnetic thin films by femtosecond optical pulses is investigated in real space. Our experimental method allows us to retrieve the three-dimensional trajectory of the magnetization vector over a large temporal range, from ∼100fsto∼1ns. This approach carries important information both on the initial spin dynamics and the magnetization precession. An ultrafast decrease of the magnetization modulus, occurring within ∼100fs, reveals the initial laser induced demagnetization. It is accompanied by a reorientation of the magnetization vector, taking place during the first picosecond, a process which strongly depends on the material anisotropy. Finally, the three-dimensional trajectory of the magnetization during its precession and damping undertakes a complex pathway as the magnetization modulus varies until the energy is dissipated to the environment in the nanosecond time scale.

Some remarks are made on the validity of a commonly used analytical model based on the rigorous coupled wave analysis to describe the optical response of one-dimensional metallic gratings.

We measure the dynamics of the quantum phase coherence of the wave function describing interacting electrons and holes optically excited into the continuum of a GaAs/AlGaAs quantum well. We achieve this by spectrally resolving both the transient four-wave mixing signal and the differential transmission signal arising from such interacting carriers. We observe a dynamical blue shift of the coherent four-wave mixing emission spectrum with respect to the excitation laser pulse and interpret this as a direct manifestation of the dynamic Coulomb correlation effects in this many-body system.

The transmission spectra of CdS platelets are studied at room temperature with a time-resolved pump-probe technique. These measurements are also performed during the switching between the two transmission levels of the bistable crystal induced by the pump pulse. In this case, the third beam from a cw argon laser holds the sample around the switching threshold. These spectral and temporally resolved experiments allow the analysis of the switching dynamics of such absorptive bistable devices. Les spectres de transmission de plaquettes de CdS sont etudies a temperature ambiante par une technique de pompe et sonde avec resolution temporelle. Ces mesures ont ete effectuees durant la commutation, induite par l'impulsion de pompe, entre les deux niveaux de transmission du bistable. Dans ce cas, le faisceau d'un laser a argon continu maintient le cristal pres du seuil de commutation. Ces experiences spectrales et resolues en temps permettent d'analyser la dynamique de commutation dans ces dispositifs bistables absorptifs.

A temporal and spectral analysis is made of high intensity nanosecond laser pulses when propagating through polycrystalline CuCl samples of different thickness. The spectral region investigated is around the two-photon resonance of the biexciton. The dynamical behaviour of the nonlinear transmission is studied when varying the laser incident intensity, its photon energy, and the sample thickness. It is shown that the experimental results can be explained, when calculating the transient dielectric function. The importance of the dynamics of excitons and biexcitons is stressed. Nous analysons le comportement temporel et spectral d'impulsions laser de quelques nanosecondes de duree et de grande intensite, lorsqu'elles se propagent dans des echantillons polycrystallins de CuCl de differentes epaisseurs. La region spectrale etudiee est la resonance biphotonique du biexciton. La dynamique de la transmission nonlineaire est mesuree en fonction de l'intensite du faisceau incident, de l'energie des photons et de l'epaisseur des echantillons. Nous montrons que les resultats experimentaux obtenus peuvent etre expliquees a partir du calcul de la fonction dielectrique transitoire. Nous mettons en evidence l'importance de la dynamique des excitons et des biexcitons.

Using the dielectric function calculated for a three-level system in the presence of two coherent light fields, renormalization effects are discussed due to a finite level population, to two-photon transitions, and to exciton—biexcition transitions for CuCl. En utilisant la fonction dielectrique calculee pour un systeme a trois niveaux en presence de deux champs coherents, nous discutons differents effets de renormalisation dus aux populations des differents niveaux, aux transitions a deux photons et aux transitions entre excitons et biexcitons dans CuCl.

At very low temperature, the reflection properties of CuCl samples under high pulsed light excitation conditions are investigated by a “pump and probe” technique. The non-linear reflection changes are shown to have different origins and different time scales: excitonic effects lead to a new reflection structure near the energy of the longitudinal exciton (∼ 1 ns time scale) and interaction with non-thermalized acoustical phonons to a decrease of the exciton reflection maximum (∼ 60 ns). Nous etudions, a tres basse temperature, par une technique de “sonde et de pompe” la reflexion d'echantillons de CuCl, places dans des conditions d'excitation intense par une source lumineuse puisee. Les changements non-lineaires de reflexion observes ont differentes origines et differentes durees: des effets excitoniques entraǐnant l'apparition d'une nouvelle structure de reflexion pres de l'energie de l'exciton longitudinal (d'une duree de l'ordre de la nanoseconde) une interaction avec des phonons acoustiques non-thermalises entraǐnant la diminution du maximum de reflexion (duree d'environ 60 ns).

Using the density matrix formalism for a three-level system, the dielectric function is derived in the presence of two exciting light fields. Different limiting situations are discussed, the approximations involved and their respective validity. En utilisant le formalisme de la matrice densite pour un systeme a trois niveaux, nous obtenons la fonction dielectrique en preeence de deux champs excitateurs. Nous discutons plusieurs cas limites, les approximations faites et leur validite respective.

An investigation is made of the transmission properties of a test beam through CuCl samples and through Fabry-Perot etalons containing CuCl under simultaneous excitation of a pump beam. For appropriately chosen photon energies of the two beams, the transmission of the test beam through the sample decreases due to nonlinear absorption, or increases when the sample is in a F.P. resonator. The switching behaviour indicates that the nonlinear absorption and dispersion properties of CuCl depend on the exciton and biexciton population dynamics. Nous etudions les proprietes de transmission d'un faisceau test a travers des echantillons de CuCI, seuls ou places dans une cavite: Fabry-Perot, exeites simultanement par un deuxieme faisceau laser intense. Pour un choix approprie des energies de photons des deux faisceaux lumineux, la transmission du faisceau test a travers l'echantillon diminue a cause de l'absorption non-lineaire ou augmente si l'echantillon est place dans une cavite Fabry-Perot. Les caracteristiques de commntation montrent que les proprietes non-linehires d'absorption et de dispersion de CuCl dependent de la dynamique des populations d'excitons et de biexcitons.

Using the density-matrix formalism, the dielectric function of athree-level system under high excitation conditions is determined. The density matrix being calculated by a continuous matrix inversion, non-resonant contributions and saturation effects can be fully accounted for and the stability of absorption and dispersion anomalies may be discussed. Nous calculons la fonction dielectrique d'un systeme a trois niveaux soumis a une forte intensite d'excitation. Le calcul, qui utilise une inversion continue de matrices appliquee au formalisme de la matrice densite, nous permet de tenir compte integralement des effets de saturation ainsi que des contributions non-resonnantes. Nous discutons egalement la stabilite des anomalies qui apparaissent dans l'absorption et dans la dispersion du systeme.

The switching dynamics of photothermal‐induced absorption optical bistability is studied in CdS. The bistable element being held near its switching threshold is switched by a pulse of an excimer laser, which can be regarded as δ shaped in time with respect to the thermal relaxation time of the sample. The dynamics of the switching process is influenced by the transverse relaxation of the temperature in the sample. Under appropriate conditions either a slowing down or a fast switching is observed.

Comparing the magnetization dynamics in CoPd films using time resolved Magneto-Optics and X-rays Magnetic Circular Dichroism, we confirm that the demagnetization dynamics of ferromagnetic metals occurs during the thermalization time of the spins.

To study the photophysical properties of the quinoidal oligothiophene derivative [QQT(CN)4], we measured the optical limiting and transient absorption properties in both solution and thin films using femtosecond laser and ultrafast pump probe experiment, respectively.

We investigated the excited state dynamics of the uv mutant of the green fluorescent protein (GFPuv) using spectrally resolved femtosecond pump–probe spectroscopy. The gain dynamics of GFPuv is characterized by a ‘slow’ picosecond mono-exponential growth contrary to the wild type (GFPwt) where ultrafast components have been previously reported. As GFPwt and GFPuv share the same chromophore, this difference can be attributed to an intrinsic improved homogeneity of the GFPuv sample. The study of a synthetic GFP chromophore allows us to confirm the key-role played by the interactions chromophore–proteic cage in GFP photophysics.

National audience; Les étapes décisives de la photoperception cellulaire sont caractérisées et suivies en temps réel par spectroscopie laser jusqu'à l'échelle de quelques dizaines de femtosecondes. Les protéines photoactives étudiées dans cet article sont impliquées dans des phénomènes naturels majeurs comme la vision (protéines de rétinal modélisées par la bactériorhodopsine), la photomotilité de microorganismes (protéine jaune photoactive et oxyblépharisminoprotéine) et le phototropisme des plantes (cryptochrome). On montre également que la protéine verte fluorescente (GFP) peut être utilisée, en amont de la thérapie génique, comme sonde temporelle de la solubilité cytoplasmique de fragments d'anticorps auxquels elle est fusionnée.

We have studied the ultrafast magnetization dynamics of ferromagnetic CoPt3 and permalloy dots. The time resolved magneto-optical Kerr measurements are performed with a confocal microscope with an accuracy of 300 nm and 150 fs. The demagnetization and the precession of the magnetization is observed in individual dots. In addition, static and time resolved images of the magnetization are made when the dot is either partially demagnetized or when it is switched to the reverse magnetization by the pump pulse.

Background CrMYC2 is an early jasmonate-responsive bHLH transcription factor involved in the regulation of the expression of the genes of the terpenic indole alkaloid biosynthesis pathway in Catharanthus roseus. In this paper, we identified the amino acid domains necessary for the nuclear targeting of CrMYC2. Findings We examined the intracellular localization of whole CrMYC2 and of various deletion mutants, all fused with GFP, using a transient expression assay in onion epidermal cells. Sequence analysis of this protein revealed the presence of four putative basic nuclear localization signals (NLS). Assays showed that none of the predicted NLS is active alone. Further functional dissection of CrMYC2 showed that the nuclear targeting of this transcription factor involves the cooperation of three domains located in the C-terminal region of the protein. The first two domains are located at amino acid residues 454-510 and 510-562 and contain basic classical monopartite NLSs; these regions are referred to as NLS3 (KRPRKR) and NLS4 (EAERQRREK), respectively. The third domain, between residues 617 and 652, is rich in basic amino acids that are well conserved in other phylogenetically related bHLH transcription factors. Our data revealed that these three domains are inactive when isolated but act cooperatively to target CrMYC2 to the nucleus. Conclusions This study identified three amino acid domains that act in cooperation to target the CrMYC2 transcription factor to the nucleus. Further fine structure/function analysis of these amino acid domains will allow the identification of new NLS domains and will allow the investigation of the related molecular mechanisms involved in the nuclear targeting of the CrMYC2 bHLH transcription factor.

Eukaryotic transcription of messenger RNAs (mRNAs) is a complex multistep process. In parallel with this fundamental mechanism, many proteins will bind to the nascent mRNA in order to process and package it to form an export competent ribonucleoprotein particle (mRNP). These mRNP biogenesis steps are under the surveillance of a quality control system (QC) that will detect all the faulty events that can lead to the formation of an aberrant particle. Aberrant transcripts will be retained in the nucleus and degraded. To study the QC mechanisms, we previously implemented a powerful assay based on the global perturbation of mRNP biogenesis by the bacterial Rho factor. When expressed in the yeast nucleus, Rho will interfere with co-transcriptional mRNP assembly and generates aberrant transcripts which will be substrates for the QC and degradation system. This study extend the previous observations made by the team about implication of some proteins in the QC pathway by genome-wide methods (RNA-seq, ChIP-seq). Moreover, study of the THO complex, which is a packaging and export factor, shows that the Tho2 subunit is involved in the tagging of aberrant transcripts and in recruitment of the exonuclease Rrp6 on its targets. Finally, we are giving insights about the presence, in yeast, of a second degradation pathway for aberrant mRNPs different from the canonical pathway involving Rrp6.; La transcription des ARN messagers (ARNm), chez les eucaryotes est un processus complexe nécessitant de nombreuses étapes. En parallèle de ce mécanisme fondamentale, de nombreuses protéines vont se fixer à l’ARNm naissant afin de le maturer et de l’empaqueter pour former une particule ribonucléoprotéique (mRNP) compétente pour l’export vers le cytoplasme, où aura lieu la traduction. Les étapes de biogénèse de cette mRNP sont soumises à la surveillance par un système de contrôle qualité (QC) qui détectera tout évènement conduisant à une mauvaise formation de la particule. Les transcrits aberrants sont retenus au noyau pour y être dégradés par l’exosome. Afin de provoquer l’apparition massive d’ARNm aberrants dans le noyau de notre modèle d’étude, la levure S. cerevisiae, nous utilisons le facteur bactérien Rho. L’hélicase translocase Rho, une fois exprimée, va venir perturber l’assemblage co-transcriptionnel des mRNPs et ainsi générer des transcrits aberrants qui seront substrats de la machinerie de QC et dégradation. La présente étude étend les précédentes observations faites par l’équipe quant à l’implication de certaines protéines dans le système de QC par des approches globales (RNA-seq, ChIP-seq). De plus, l’étude du complexe THO, impliqué dans l’empaquetage et le transport de la mRNP, révèle l’implication d’une de ses sous-unités dans le marquage des ARNm aberrants ainsi qu’un lien de première importance dans le recrutement de l’exonucléase Rrp6 sur ces cibles à dégrader. Enfin, nous montrons, de manière globale l’existence, au sein du noyau des levures, d’une seconde voie de dégradation des ARNs aberrants distincte de la voie canonique passant par Rrp6.

Eukaryotic transcription of messenger RNAs (mRNAs) is a complex multistep process. In parallel with this fundamental mechanism, many proteins will bind to the nascent mRNA in order to process and package it to form an export competent ribonucleoprotein particle (mRNP). These mRNP biogenesis steps are under the surveillance of a quality control system (QC) that will detect all the faulty events that can lead to the formation of an aberrant particle. Aberrant transcripts will be retained in the nucleus and degraded. To study the QC mechanisms, we previously implemented a powerful assay based on the global perturbation of mRNP biogenesis by the bacterial Rho factor. When expressed in the yeast nucleus, Rho will interfere with co-transcriptional mRNP assembly and generates aberrant transcripts which will be substrates for the QC and degradation system. This study extend the previous observations made by the team about implication of some proteins in the QC pathway by genome-wide methods (RNA-seq, ChIP-seq). Moreover, study of the THO complex, which is a packaging and export factor, shows that the Tho2 subunit is involved in the tagging of aberrant transcripts and in recruitment of the exonuclease Rrp6 on its targets. Finally, we are giving insights about the presence, in yeast, of a second degradation pathway for aberrant mRNPs different from the canonical pathway involving Rrp6., La transcription des ARN messagers (ARNm), chez les eucaryotes est un processus complexe nécessitant de nombreuses étapes. En parallèle de ce mécanisme fondamentale, de nombreuses protéines vont se fixer à l’ARNm naissant afin de le maturer et de l’empaqueter pour former une particule ribonucléoprotéique (mRNP) compétente pour l’export vers le cytoplasme, où aura lieu la traduction. Les étapes de biogénèse de cette mRNP sont soumises à la surveillance par un système de contrôle qualité (QC) qui détectera tout évènement conduisant à une mauvaise formation de la particule. Les transcrits aberrants sont retenus au noyau pour y être dégradés par l’exosome. Afin de provoquer l’apparition massive d’ARNm aberrants dans le noyau de notre modèle d’étude, la levure S. cerevisiae, nous utilisons le facteur bactérien Rho. L’hélicase translocase Rho, une fois exprimée, va venir perturber l’assemblage co-transcriptionnel des mRNPs et ainsi générer des transcrits aberrants qui seront substrats de la machinerie de QC et dégradation. La présente étude étend les précédentes observations faites par l’équipe quant à l’implication de certaines protéines dans le système de QC par des approches globales (RNA-seq, ChIP-seq). De plus, l’étude du complexe THO, impliqué dans l’empaquetage et le transport de la mRNP, révèle l’implication d’une de ses sous-unités dans le marquage des ARNm aberrants ainsi qu’un lien de première importance dans le recrutement de l’exonucléase Rrp6 sur ces cibles à dégrader. Enfin, nous montrons, de manière globale l’existence, au sein du noyau des levures, d’une seconde voie de dégradation des ARNs aberrants distincte de la voie canonique passant par Rrp6.

The goal of this thesis is to develop an harmonic source to cover the energy range of 50-70 eV of the electromagnetic spectrum by high harmonic generation in a rare gas. This source called "tabletop" is obtained from a femtosecond laser system based on the chirped pulse amplification technique. Such source allows probing the magnetization dynamics at the M-edges of transition metals. The interest to probe the magnetization dynamics with X-rays is the chemical selectivity on the elements. This, one can probe the spin dynamics of the chemical element which are responsible for magnetism. For example, in a system containing several elements, one can reach the magnetic properties of each one of its components by adjusting the photon energy to the absorption edge of the element.; L’objectif de cette est de développer une source harmonique permettant de couvrir la gamme d’énergie 50 -70 eV du spectre électromagnétique par la génération d’harmoniques d’ordre élevé dans un gaz rare. Cette source appelée "tabletop" est obtenue à partir d’un système laser femtoseconde basé sur la technique d’amplification à dérive de fréquence. Une telle source permet de réaliser des expériences de dynamique des charges et de l’aimantation aux seuils M des métaux de transition. L’intérêt de sonder la dynamique de l’aimantation dans le domaine des rayons X est la sélectivité chimique sur les éléments. Grâce à la sélectivité chimique, on peut sonder la dynamique des spins des espèces chimiques qui sont responsables du magnétisme. Par exemple, dans un système contenant plusieurs éléments, on peut accéder aux propriétés magnétiques de chacun de ses composants en ajustant l’énergie des photons au seuil d’absorption de l’élément choisi.

One of the goals of Femtomagnetism is to manipulate the magnetization of materials using femtosecond optical pulses. It has been shown in ferromagnetic films that a magneto-optical (MO) coherent response takes place before the thermalization of the spins populations in a pump and probe MOKE experiment. It results from the coherent spin-photon coupling mediated by the spin-orbit interaction. A simplified description of this effect has been made by considering an eight-level system coupled with the laser field. The MO coherence can be defined by the magnetic field dependent dephasing time T2MO. In the present work, it is shown that the coherent MO response of a bismuth-doped garnet can be directly measured in different degenerated MO four-wave mixing configurations. The importance of well-knowing the spectral phase of the pulse to measure T2MO was studied. Using 10fs near infra-red pulses, T2MO was shown to be (2.8+/-1)fs that is of the same order of the charges dephasing time.; Un des objectifs du Femtomagnetisme est de contrôler l’aimantation des matériaux avec des impulsions laser femtoseconde. Il a été démontré qu’une réponse magnéto-optique (MO) cohérente a lieu avant la thermalisation des populations de spins dans une configuration pompe-sonde MOKE. Elle résulte du couplage cohérent spin-photon dû à l’interaction spin-orbite. Une description simplifiée de cet effet a été faite en tenant compte d’un système à huit niveaux couplés au champ laser. La cohérence MO est définie par le temps de déphasage dépendent du champ T2MO. Dans ce travail, il est montré que la réponse MO cohérente d’un grenat dopé au bismuth peut être mesurée directement avec différentes configurations de mélange à quatre ondes MO. L’importance de connaître la phase spectrale de l’impulsion pour obtenir T2MO a été étudié. Avec des impulsions de 10fs dans le proche infra-rouge, une mesure de T2MO donne (2.8+/-1)fs, c. à d., du même ordre de grandeur que le temps de déphasage des charges.

International audience; The development of numerous programs for the identification of mobile elements raises the issue of the founding concepts that are shared in their design. This is necessary for at least three reasons. First, the cost of designing, developing, debugging and maintaining software could present a danger of distracting biologists from their main bioanalysis tasks that require a lot of energy. Some key concepts on exact repeats are always underlying the search for genomic repeats and we recall the most important ones. All along the chapter, we try to select practical tools that may help the design of new identification pipelines. Second, the huge increase of sequence production capacities requires to use the most efficient data structures and algorithms to scale up tools in front of the data deluge. This paper provides an up-to-date glimpse on the art of string indexing and string matching. Third, there exists a growing knowledge on the architecture of mobile elements built from literature and the analysis of results generated by these pipelines. Besides data management which has led to the discovery of new families or new elements of a family, the community has an increasing need in knowledge management tools in order to compare, to validate or simply to keep trace of mobile elements models. We end the paper with first considerations on what could help the near future of such research on models.

Transposable elements (TEs) are discrete pieces of DNA that can move from one site to another within genomes and sometime between genomes. They are found in all major branches of life. Because of their wide distribution and considerable diversity, they are a considerable source of genomic variation and as such, they constitute powerful drivers of genome evolution. Moreover, it is becoming clear that the epigenetic regulation of certain genes is derived from defense mechanisms against the activity of ancestral transposable elements. TEs now tend to be viewed as natural molecular tools that can reshape the genome, which challenges the idea that TEs are natural tools used to answer biological questions. In the first part of this chapter, we review the classification and distribution of TEs, and look at how they have contributed to the structural and transcriptional reshaping of genomes. In the second part, we describe methodological innovations that have modified their contribution as molecular tools.

The thesis deals with experimental studies of the laser induced spin dynamics in magnetic nanostructures. First, we studied the spin dynamics of individual ferromagnetic discs of CoPt3 and permalloy (the diameter vary from 0.25 μm to 30 μm). The experimental set-up consists in time resolved Kerr magneto-optical pump probe measurements in the confocal geometry (the spatial resolution is 300 nm; the temporal resolution is 150 fs). We showed that the spin dynamics depends strongly on the pump intensity particularly the spin-lattice time relaxation and the frequency of magnetization precession. We also studied the spatial expansion of the demagnetisation in a single dot. Additionally, we developed a powerful technique named Magneto-Optical Pump Probe Imaging (MOPPI) used for studying the magnetization switching in CoPt films and in individual dots. We explored the influence of different parameters: the laser intensity, the external static magnetic field, and the crystalline character of the sample (alloy, multilayer) on the magnetization switching. Finally, we performed Magnetic Force Microscopy imaging of the laser induced magnetic domains. We also studied the coherent spin dynamics of magnetic nanoparticles (the average diameter varies from 2 nm to 10 nm) excited with femtosecond laser pulses. The analysis of the three spatial components of the magnetization (polar, longitudinal, and transverse) after the optical excitation (> 120 fs) brings useful information about the ultrafast demagnetization, the gyroscopic motion (precession and damping of the magnetization) that preceeds the super-paramagnetic fluctuations. We explored the influence of the magnetic anisotropy on the ultrafast reorientation of the magnetization and we demonstrated that the damping increases when the diameter of particles decreases., La thèse traite d'un point de vue expérimental la dynamique d'aimantation induite par laser femtoseconde de nanostructures magnétiques. En premier lieu, nous nous sommes intéressés à la dynamique de spins dans des plots ferromagnétiques individuels de CoPt3 et de permalloy (le diamètre varie de 0.25 à 30 Μm). Le montage expérimental consiste en des mesures magnéto-optique Kerr pompe sonde en géométrie confocale (la résolution spatiale est 300 nm ; la résolution temporelle est 150 fs). Nous avons montré que la dynamique d'aimantation dépend fortement de la densité d'excitation laser notamment le temps de relaxation spin-réseau et la fréquence de précession. Nous avons également étudié l'expansion spatiale de la désaimantation dans un plot individuel. De plus, nous avons développé une technique d'imagerie résolue en temps permettant d'étudier le renversement d'aimantation dans des films et plots individuels de CoPt. Nous avons exploré l'effet des différents paramètres : intensité laser, champ magnétique appliqué, et la nature cristalline du substrat (alliage, multicouches) sur le renversement d'aimantation. Enfin, nous avons étudié par microscope à force magnétique la structure des domaines magnétiques induite par laser. Nous avons également étudié la dynamique cohérente d'aimantation de nanoparticules magnétiques (le diamètre moyen varie de 2 à 10 nm) excitées par des impulsions laser. L'analyse de la trajectoire d'aimantation dans les trois directions de l'espace (polaire, longitudinal, transverse) après l'excitation optique (> 120 fs) nous a permis de mettre en évidence la désaimantation ultrarapide (~ 200 fs), le mouvement gyroscopique de l'aimantation (précession et l'amortissement de l'aimantation) qui précède les fluctuations super-paramagnétiques. Nous avons exploré le rôle de l'anisotropie magnétique sur la réorientation initiale de l'aimantation et nous avons montré que le damping augmente avec la diminution de la taille de particules.

During this project, we have developed a new far field optical imaging technique,called Photothermal Heterodyne Imaging, which allows for highly sensitive, "background-free"detection of a large variety of individual absorbing nano-objects (metallic nanoparticles with diameterdown to 1.4 nm, semiconductor nanocrystals, carbon nanotubes,. . .) . The photothermalsignal was characterized experimentally on individual gold nanoparticles. Our measurements arein excellent agreement with analytical calculations based on an electrodynamical model. Sincethe photothermal signal arising from an isolated nana-object is directly proportional to the absorbedpower, the PHI method opens new pathways towards quantitative absorption spectroscopy.Surface Plasmon Resonance spectra of individual gold nanoparticles with diameters from 5 to 33nm were recorded. Intrinsic size were unambiguously observed and analyzed within the frame ofMie theory. Absorption spectroscopy of individual CdSe nanocrystals in the multiexcitonic regimewas also performed. The physical origin of the photothermal signal is discussed by confrontingthe photothermal absorption spectrum and the emission spectrum of a same nanocrystal. Finally,the structure of individual semiconducting and metallic carbon nanotubes was characterized afteranalysis of their absorption spectra around the lowest optical resonances., Ce manuscrit décrit le développement de la technique d'Imagerie PhotothermiqueHétérodyne (PHI). Cette nouvelle méthode optique en champ lointain permet de détecter unegrande variété de nano-objets individuels absorbants (nanoparticules métalliques jusqu'à 1.4 nmde diamètre, nanocristaux semiconducteurs, nanotubes de carbone métalliques et semiconducteurs,.. .), sur un fond « noir », avec un très bon rapport signal à bruit. Le signal photothermiquea été caractérisé expérimentalement sur des nanoparticules d'or individuelles. Les mesures obtenuessont comparées à des calculs analytiques issus d'un modèle électrodynamique. Etant donnéque ce signal est directement proportionnel à la puissance absorbée, la méthode PHI ouvre lavoie à des expériences de spectroscopie d'absorption à l'échelle du nano-objet individuel. Dansun premier temps, nous avons sondé la résonance plasmon de surface de nanoparticules d'orindividuelles de 5 à 33 nm de diamètre. Cette étude a abouti à l'observation d'effets de tailleintrinsèques, analysés dans le cadre de la théorie de Mie. Nous avons ensuite mesuré les spectresd'absorption de nanocristaux individuels de CdSe en régime multiexcitonique. Pour un mêmenanocristal, la comparaison des spectres d'absorption photothermique et d'émission permet dediscuter l'origine physique du signal photothermique. Enfin, nous avons caractérisé la structurede nanotubes de carbone semiconducteurs et métalliques individuels en analysant leurs spectresd'absorption autour de leurs premières résonances optiques.