The checkpoint Saccharomyces cerevisiae Rad9 protein contains a tandem tudor domain that recognizes DNA.

International audienceDNA damage checkpoints are signal transduction pathways that are activated after genotoxic insults to protect genomic integrity. At the site of DNA damage, 'mediator' proteins are in charge of recruiting 'signal transducers' to molecules 'sensing' the damage. Budding yeast Rad9, fission yeast Crb2 and metazoan 53BP1 are presented as mediators involved in the activation of checkpoint kinases. Here we show that, despite low sequence conservation, Rad9 exhibits a tandem tudor domain structurally close to those found in human/mouse 53BP1 and fission yeast Crb2. Moreover, this region is important for the resistance of Saccharomyces cerevisiae to different genotoxic stresses. It does not mediate direct binding to a histone H3 peptide dimethylated on K79, nor to a histone H4 peptide dimethylated on lysine 20, as was demonstrated for 53BP1. However, the tandem tudor region of Rad9 directly interacts with single-stranded DNA and double-stranded DNAs of various lengths and sequences through a positively charged region absent from 53BP1 and Crb2 but present in several yeast Rad9 homologs. Our results argue that the tandem tudor domains of Rad9, Crb2 and 53BP1 mediate chromatin binding next to double-strand breaks. However, their modes of chromatin recognition are different, suggesting that the corresponding interactions are differently regulated

Undulator design for Laser Plasma Based Free electron laser

The fourth generation of synchrotron radiation sources, commonly referred to as the Free Electron Laser (FEL), provides an intense source of brilliant X-ray beams enabling the investigation of matter at the atomic scale with unprecedented time resolution. These sources require the use of conventional linear accelerators providing high electron beam performance. The achievement of chirped pulse amplification allowing lasers to be operated at the Terawatt range, opened the way for the Laser Plasma Acceleration (LPA) technique where high energy electron bunches with high current can be produced within a very short centimeter-scale distance. Such an advanced acceleration concept is of great interest to be qualified by an FEL application for compact X-ray light sources. We explore in this paper what the LPA specificities imply on the design of the undulator, part of the gain medium. First, the LPA concept and state-of-art are presented showing the different operation regimes and what electron beam parameters are likely to be achieved. The LPA scaling laws are discussed afterwards to better understand what laser or plasma parameters have to be adjusted in order to improve electron beam quality. The FEL is secondly discussed starting with the spontaneous emission, followed by the different FEL configurations, the electron beam transport to the undulator and finally the scaling laws and correction terms in the high gain case. Then, the different types of compact undulators that can be implemented for an LPA based FEL application are analyzed. Finally, examples of relevant experiments are reported by describing the transport beamline, presenting the spontaneous emission characteristics achieved so far and the future prospects

The ThomX project status

Work supported by the French Agence Nationale de la recherche as part of the program EQUIPEX under reference ANR-10-EQPX-51, the Ile de France region, CNRS-IN2P3 and Université Paris Sud XI - http://accelconf.web.cern.ch/AccelConf/IPAC2014/papers/wepro052.pdfA collaboration of seven research institutes and an industry has been set up for the ThomX project, a compact Compton Backscattering Source (CBS) based in Orsay - France. After a period of study and definition of the machine performance, a full description of all the systems has been provided. The infrastructure work has been started and the main systems are in the call for tender phase. In this paper we will illustrate the definitive machine parameters and components characteristics. We will also update the results of the different technical and experimental activities on optical resonators, RF power supplies and on the electron gun

Injection d'un laser à électrons libres (exemples de SPARC, UVSOR-II et perspectives pour ARC-EN-CIEL)

Ce travail porte sur le fonctionnement d un Laser a Electrons Libres (LEL) en configuration Injectée. Trois exemples sont présentés : celui de UVSOR-II (Okazaki, Japon), celui de SPARC (Frascati, Italie) et ceux du projet ARC-EN-CIEL (France). Sur l exemple de UVSOR-II, injecté avec un laser Ti :Sa a 1 kHz, des thématiques variées ont et e abordées : dynamique électronique, cohérence spatiale, structure spectrale et distribution angulaire du rayonnement, optimisation de la source avec une polarisation variable. Sur l exemple de SPARC, l injection d une source harmonique générée dans les gaz (HHG) est envisagée. Cette combinaison originale, offrant un rayonnement spatialement et temporellement cohérent de forte intensité de l UV aux rayons X, constitue une source d avenir. Une source harmonique dédiée a et e mise au point pour le LEL de SPARC et devrait permettre d ici fin 2008, outre des études systématiques de la combinaison LEL-HHG, la démonstration de nouvelles configurations de LEL injectés. Enfin, au cours des simulations effectuées pour le dimensionnement des sources de rayonnement d ARC-EN-CIEL, un nouveau régime de propagation de l impulsion LEL a été observé et reste en cours d etude.This work presents a general study on Free Electron Lasers (FEL) in the seeded configuration. Three examples are given : the UVSOR-II FEL (Okazaki, Japan), the SPARC FEL (Frascati, Italy) and the ARC EN CIEL project FEL (France). In the case of the UVSOR II FEL, seeded with a Ti :Sa laser at 1 kHz repetition rate, several studies have been performed : electron beam dynamics, spatial coherence, spectral structure and angular distribution of the radiation, optimization in helical mode. In the case of the SPARC FEL, the injection of a harmonic source generated in rare gas (HHG) is foreseen. This original combination stands as an attractive source for users with a high temporal and spatial coherence degree together with a high intensity from UV to X rays. A dedicated harmonic source has been designed, assembled and tested for the SPARC FEL. The operation of the combined devices should start in Winter 2008, allowing fine characterization of the HHG-FEL association and further demonstration of original HGHG FELs configuration. Finally, during the simulation studies performed for the design of the ARC EN CIEL light sources, a new propagation regime of the FEL pulse has been observed and is still under study.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF