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International audience; Viruses are obligate parasites that rely on their host's cellular machinery for replication. To facilitate their replication cycle, many viruses have been shown to remodel the cellular architecture by inducing the formation of membraneless organelles (MLOs). Eukaryotic cells have evolved MLOs that are highly dynamic, self-organizing microenvironments that segregate biological processes and increase the efficiency of reactions by concentrating enzymes and substrates. In the context of viral infections, MLOs can be utilized by viruses to complete their replication cycle. This review focuses on the pathway used by the HIV-1 virus to remodel the nuclear landscape of its host, creating viral/host niches that enable efficient viral replication. Specifically, we discuss how the interaction between the HIV-1 capsid and the cellular factor CPSF6 triggers the formation of nuclear MLOs that support nuclear reverse transcription and viral integration in favored regions of the host chromatin. This review compiles current knowledge on the origin of nuclear HIV-MLOs and their role in early post-nuclear entry steps of the HIV-1 replication cycle.

International audience

International audience; A number of studies across different model systems revealed that chromatin undergoes significant changes in dynamics in response to DNA damage. These include local motion changes at damage sites, increased nuclear exploration of both damaged and undamaged loci, and directed motions to new nuclear locations associated with certain repair pathways. These studies also revealed the need for new analytical methods to identify directed motions in a context of mixed trajectories, and the importance of investigating nuclear dynamics over different time scales to identify diffusion regimes. Here we provide an overview of the current understanding of this field, including imaging and analytical methods developed to investigate nuclear dynamics in different contexts. These dynamics are essential for genome integrity. Identifying the molecular mechanisms responsible for these movements is key to understanding how their misregulation contributes to cancer and other genome instability disorders.

Among the five-year government-funded World Class University Projects in Korea, the category-3 program approved at Hanyang University in Seoul led to an exploratory effort to go from neutron-rich nuclei to dense matter in neutron stars. The principal results in what transpired in the effort -- and what followed afterwards -- are described with the focus on the possibly important, hitherto unexplored, role played in nuclear dynamics of topology and hidden symmetries of QCD. The potential link to the proton mass problem is pointed out., 16 pages, no figures; invited paper to IJMPE, references corrected

International audience; We present a theoretical model to investigate double-core-hole-state formation in molecules through sequential absorption of two x-ray photons from a femtosecond laser pulse. A complete time-dependent quantum description taking into account x-ray absorption and nuclear dynamics explicitly and Auger decay phenomenologically is established within the local approximation. Using this model, we assess the impact of the nuclear dynamics on double-core photoionization processes in the case of the carbon monoxide molecule. We show that sequential absorption of two x-ray photons modifies significantly the vibrational distribution of the photoelectron spectra of the double-core-hole states compared to direct single x-ray photon absorption. Depending on the shape of the potential energy curves involved in the sequential absorption processes, lower or higher vibrational levels may be favored. Furthermore, in the case where the final state is dissociative, the electron spectrum is further broaden and blue-shifted in the two-photon process.

International audience; Creation of deep core holes leads to extensive nuclear dynamics on a few femtosecond timescale despite the very short (τ ≤ 1 fs) lifetime of such states. This is because the 1st steps of the relaxation processes (i.e. both radiative and non-radiative decays) generate intermediate states with one and multiple holes in core orbitals. As an example, ultrafast dissociation is observed in three well-distinguishable LVV Auger decay channels for HCl following Cl1s→σ* excitation.

Proteins engaged in macromolecular complexes interacting with chromatin move throughout the nucleus by diffusive processes, transiently and repetitively contacting their target sites. Diffusion and interactions play important roles in gene expression by defining the target gene search time. In the work presented in this thesis we monitored the mobility of the Positive Transcription Elongation factor b (P-TEFb) responsible for the phosphorylation of the RNA polymerase II C-terminal domain and showed that its relatively high mobility is regulated by the 7SK small nuclear ribonucleoprotein complex (7SK snRNP). Without the 7SK regulating complex, transient interactions of the P-TEFb cycline T1 component with RNA polymerase II prevent the nuclear distribution of the elongation factor therefore restricting its activity to sites of high polymerase concentration and limiting its recruitment to new sites. This observation demonstrates that the fast mobility of proteins required for the stochastic assembly of nuclear molecular machines is not only a physical property of macromolecules but a biophysical parameter tightly controlled by cellular regulators., Cette thèse a pour but l'analyse de la dynamique de facteurs de transcription dans le noyau. Les interactions entre molécules nucléaires dans des cellules vivantes ont été décrites comme étant suffisamment transitoires pour que la dynamique de ces molécules puisse être considérée comme étant de la diffusion effective [MISTELI2001, PHAIR]. Etant donné la géométrie des chemins possibles dans le noyau et la haute densité de ce compartiment en molécules diverses, il a été démontré par de nombreux calculs que la diffusion est non seulement le moyen de transport la moins gourmande en énergie, mais également la plus efficace. Ceci nous mène à nous demander comment la cellule permet de contrôler son état transcriptionnel global au vu de la nature stochastique du déplacement de ces facteurs de transcription. Jusqu'à présent, la recherche de cible a été souvent étudiée en utilisant le " temps de premier passage ", c'est-à-dire le temps que met une particule diffusant librement pour atteindre sa cible. Dans le cas d'un compartiment aussi complexe que le noyau, où de nombreuses interactions non spécifiques peuvent avoir lieu, et avec une quantité limitée de protéines distribuées de façon homogène, le temps nécessaire pour qu'une protéine trouve sa cible est en complet décalage avec l'efficacité à laquelle fonctionnent les systèmes biologiques.

Proteins engaged in macromolecular complexes interacting with chromatin move throughout the nucleus by diffusive processes, transiently and repetitively contacting their target sites. Diffusion and interactions play important roles in gene expression by defining the target gene search time. In the work presented in this thesis we monitored the mobility of the Positive Transcription Elongation factor b (P-TEFb) responsible for the phosphorylation of the RNA polymerase II C-terminal domain and showed that its relatively high mobility is regulated by the 7SK small nuclear ribonucleoprotein complex (7SK snRNP). Without the 7SK regulating complex, transient interactions of the P-TEFb cycline T1 component with RNA polymerase II prevent the nuclear distribution of the elongation factor therefore restricting its activity to sites of high polymerase concentration and limiting its recruitment to new sites. This observation demonstrates that the fast mobility of proteins required for the stochastic assembly of nuclear molecular machines is not only a physical property of macromolecules but a biophysical parameter tightly controlled by cellular regulators.; Cette thèse a pour but l'analyse de la dynamique de facteurs de transcription dans le noyau. Les interactions entre molécules nucléaires dans des cellules vivantes ont été décrites comme étant suffisamment transitoires pour que la dynamique de ces molécules puisse être considérée comme étant de la diffusion effective [MISTELI2001, PHAIR]. Etant donné la géométrie des chemins possibles dans le noyau et la haute densité de ce compartiment en molécules diverses, il a été démontré par de nombreux calculs que la diffusion est non seulement le moyen de transport la moins gourmande en énergie, mais également la plus efficace. Ceci nous mène à nous demander comment la cellule permet de contrôler son état transcriptionnel global au vu de la nature stochastique du déplacement de ces facteurs de transcription. Jusqu'à présent, la recherche de cible a été souvent étudiée en utilisant le " temps de premier passage ", c'est-à-dire le temps que met une particule diffusant librement pour atteindre sa cible. Dans le cas d'un compartiment aussi complexe que le noyau, où de nombreuses interactions non spécifiques peuvent avoir lieu, et avec une quantité limitée de protéines distribuées de façon homogène, le temps nécessaire pour qu'une protéine trouve sa cible est en complet décalage avec l'efficacité à laquelle fonctionnent les systèmes biologiques.

The temporal dynamics of double ionization of ${\text{H}}_{2}$ has been investigated both experimentally and theoretically with few-cycle laser pulses. The main observables are the proton spectra associated with the ${\text{H}}^{+}+{\text{H}}^{+}$ fragmentation channel. The model is based on the time-dependent Schr\"odinger equation and treats the electronic and nuclear coordinates on the same level. Therefore it allows the ultrafast nuclear dynamics to be followed as a function of the laser pulse duration, carrier-envelope phase offset, and peak intensity. We mainly report results in the sequential double-ionization regime above $2\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.3em}{0ex}}\text{W}\phantom{\rule{0.2em}{0ex}}{\text{cm}}^{\ensuremath{-}2}$. The proton spectra are shifted to higher energies as the pulse duration is reduced from 40 down to 10 fs. The good agreement between the model predictions and the experimental data at 10 fs permits a theoretical study with pulse durations down to a few femtoseconds. We demonstrate the very fast nuclear dynamics of the ${\text{H}}_{2}{}_{+}$ ion for a pulse duration as short as 1 fs between the two ionization events, giving $\text{H}_{2}{}^{+}$ from ${\text{H}}_{2}$ and ${\text{H}}^{+}+{\text{H}}^{+}$ from $\text{H}_{2}{}^{+}$. The carrier-envelope phase offset plays a significant role only for pulse durations shorter than 4 fs. At 10 fs, the laser intensity dependence of the proton spectra is fairly well reproduced by the model.

International audience

Molecular imaging in living cells or organisms now allows us to observe macromolecular assemblies with a time resolution sufficient to address cause-and-effect relationships on specific molecules. These emerging technologies have gained much interest from the scientific community since they have been able to reveal novel concepts in cell biology, thereby changing our vision of the cell. One main paradigm is that cells stochastically vary, thus implying that population analysis may be misleading. In fact, cells should be analyzed within time-resolved single-cell experiments rather than being compared to other cells within a population. Technological imaging developments as well as the stochastic events present in gene expression have been reviewed. Here, we discuss how the structural organization of the nucleus is revealed using noninvasive single-cell approaches, which ultimately lead to the resolution required for the analysis of highly controlled molecular processes taking place within live cells. We also describe the efforts being made towards physiological approaches within the context of living organisms.

The purpose and contents of this topical issue, Dynamics and Thermodynamics with Nuclear Degrees of Freedom, which grew out of a series of workshops in the years 2004 and 2005, are introduced. The central topics are the nuclear density functional, nuclear multi-fragmentation, and nuclear phase transitions.

Using a five-state, all-mode vibronic coupling model Hamiltonian derived in a previous publication [A. Markmann et al., J. Chem. Phys. 122, 144320 (2005)], we have calculated the photoelectron spectrum of the pentatetraene cation in the neighborhood of the B (2)E state, which can be represented with charge-localized components. To this end, quantum nuclear dynamics calculations were performed using the multiconfiguration time-dependent Hartree method, taking all 21 vibrational normal modes into account. Compared to experiment, the main features are reproduced but higher accuracy experiments are necessary to gauge the accuracy of the predictions for the vibronic progressions at the rising flank of the spectrum.

Experimental results concerning the Ni-58 + Ni-58 at 30 MeV/u and Ni-58 + Au-197 at 30 and 45 MeV/u reactions are presented. The emission mechanism of hard photons has been exploited to get information on the time evolution of the reactions. From the measured hard gamma multiplicity associated to different classes of heavy residues a quantitative estimate of the reaction centrality has been obtained. Moreover, evidence of a prompt Intermediate Mass Fragment (IMF) emission is shown for the Ni + Au reaction at 45 MeV/u for central collisions exploring the correlation function between thermal photons and IMF's.

The reaction dynamics has been investigated in the 58Ni+58Ni at 30 MeV/u reaction studying energetic proton emission and heavy residue features. Moreover, measuring the hard gamma multiplicity associated to different classes of heavy residues we achieve a quantitative measurement of the reaction centrality. Experimental data have been also compared with dynamical calculations. Protons with energy exceeding more than five times the incident energy per nucleon were measured and their impact parameter dependence seems to indicate the presence of cooperative processes.

URL: http://www-spht.cea.fr/articles/T96/149 Dynamique nucléaire chirale

Motivated by the feasibility of microscopic calculations of the nuclear collective motion we present a practical method for calculating the zero-point energy corrections on the potential energy surfaces. For the case of quadrupole motion, as described by Bohr's Hamiltonian, the zero-point energy corrections are of vibrational and rotational nature. They can be computed in the framework of a theory based on approximations to the generator coordinate method. We present simple prescriptions for the calculation of both quantities. The coupling of vibrational and rotational degrees of freedom at small deformations is dealt with in a simple way. The importance of the zero-point energy correction is exhibited in a static (Hartree-Fock-Bogoliubov) and a dynamic study of 58 Ni.