Prospectives

Tiré de: Prospectives, vol. 3, no 1 (février 1967)Titre de l'écran-titre (visionné le 24 janv. 2013

Prospectives

Tiré de: Prospectives, vol. 3, no 2 (avril 1967)Titre de l'écran-titre (visionné le 24 janv. 2013

Prospectives

Tiré de: Prospectives, vol. 3, no 2 (avril 1967)Titre de l'écran-titre (visionné le 24 janv. 2013

Regulation of Tubulin dynamics by the +Tip tracking protein Mal3

The Microtubule (MT) network is a central component of the eukaryotic cell cytoskeleton. In the fission yeast S. pombe, a complex of three proteins specifically tracks MT +ends and stabilizes MTs in the cell. It is composed of the proteins Mal3, Tip1 and Tea2. Mal3, the S. pombe homologue of EB1, is a highly conserved ubiquitous protein found to be at the centre of many MT related processes. Tip1 is a CLIP170 homologue and Tea2 a kinesin-like motor protein. The mechanism by which they target the growing end of MTs and stabilize them is still unknown. A combination of biochemistry, electron microscopy and crystallography were used in an attempt to get a more precise understanding of the MT stabilization by this +Tip complex. Protein-A pull-down of the endogenous complex and analysis of its constituents by mass spectrometry revealed that Tea2 and Tip1 form a tight stoichiometric complex, making a much more labile interaction with Mal3. Biochemical experiments, light scattering and DIC microscopy demonstrate that Mal3 stabilizes the MT structure in a stoichiometric fashion by suppressing catastrophe events. 3D helical reconstruction of electron micrographs of Mal3 bound to the MT show that it most probably stabilizes the MT structure by bridging protofilaments together. Deletion mutant analysis suggests that contact with one of the protofilaments is via an interaction between the charged tails of tubulin and Mal3. Mal3 MT binding domain structure was solved by X-ray crystallography so that eventually it may be docked into a higher resolution electron microscopy map to provide a more precise structural insight on how Mal3 stabilizes the MT lattice. The EM analysis also shows that Mal3 regulates MT structure in vitro by restraining their protofilament number to 13, which is the number always found in vivo, and by driving the assembly of MTs with a high proportion of A-lattice. It is the first time that a protein is found to promote formation of A-lattice MTs. The fact that EB1 is such a ubiquitous protein reopens the question of MT structure in cells and has important implications for in vivo MT dynamics.Rob Cros

Prospectives

Tiré de: Prospectives, vol. 2, no 6 (déc. 1966)Titre de l'écran-titre (visionné le 24 janv. 2013

L’arme non létale dans la stratégie militaire des Etats-Unis : imaginaire stratégique et genèse de l’armement

Cette analyse a pour but de dégager les attenants du processus de légitimation dont le concept de non-létalité a fait l’objet au sein du débat stratégique américain depuis le début des années 1990. La mise en service expérimentale en 2006 en Irak, dans le contexte de la gestion post-conflit, de systèmes non létaux à énergie dirigée, destinés au contrôle des foules et à la protection des postes de garde rappelle l’actualité cruciale du phénomène. Présentées comme potentiellement révolutionnaires, ces armes « non létales » de nouvelle génération, aujourd’hui requalifiées dans la doctrine militaire comme « armes à létalité réduite », représentent sans aucun doute une mutation épistémologique majeure dans l’histoire de la conception et de la production de l’armement. Cet article vise à analyser la portée réelle et les faux-semblants de cette supposée rupture stratégique et tactique. Il ne sera pas fait ici état, sinon de manière marginale, des enjeux juridiques liés à la non-létalité.This article focuses on the process of legitimization of the concept of non-lethality that has developed in the US strategic debate since the 1990’s. The experimental use in 2006 in Iraq, in the contexte of the management of the post-conflict phase, of energy directed non-lethal weapons systems, in order to contribute to crowd control and the protection of checkpoints, shows the topicality of the phenomenon. Presented as potentially revolutionnary, these new generation of “non-lethal” weapons, currently dubbed “less than lethal”, undoubtely represents a major epistemic shift in the history of the conception and production of weapons systems. This article aims at analyzing the actual reach and pretences of this supposed strategic and tactical breakthrough. The legal aspects of non-lethality will not be considered here

Géologie du Sahara algérien et aperçu géologique sur le Sahara de l'Océan Atlantique à la Mer Rouge. Texte

Extrait des documents relatifs à la mission de Laghouat - el-Goléa - Ouargla - Biskra

Engineered ferritin for lanthanide binding

Ferritin H-homopolymers have been extensively used as nanocarriers for diverse applications in the targeted delivery of drugs and imaging agents, due to their unique ability to bind the transferrin receptor (CD71), highly overexpressed in most tumor cells. In order to incorporate novel fluorescence imaging properties, we have fused a lanthanide binding tag (LBT) to the C-terminal end of mouse H-chain ferritin, HFt. The HFt-LBT possesses one high affinity Terbium binding site per each of the 24 subunits provided by six coordinating aminoacid side chains and a tryptophan residue in its close proximity and is thus endowed with strong FRET sensitization properties. Accordingly, the characteristic Terbium emission band at 544 nm for the HFt-LBT Tb(III) complex was detectable upon excitation of the tag enclosed at two order of magnitude higher intensity with respect to the wtHFt protein. X-ray data at 2.9 Å and cryo-EM at 7 Å resolution demonstrated that HFt-LBT is correctly assembled as a 24-mer both in crystal and in solution. On the basis of the intrinsic Tb(III) binding properties of the wt protein, 32 additional Tb(III) binding sites, located within the natural iron binding sites of the protein, were identified besides the 24 Tb(III) ions coordinated to the LBTs. HFt-LBT Tb(III) was demonstrated to be actively uptaken by selected tumor cell lines by confocal microscopy and FACS analysis of their FITC derivatives, although direct fluorescence from Terbium emission could not be singled out with conventional, 295–375 nm, fluorescence excitation