The Devon Island Expedition

In 1959 the Arctic Institute of North America undertook an integrated program of long term research on Devon Island in the Queen Elizabeth Islands of arctic Canada. The co-ordinated studies were designed to help understand the interrelationships between the glacier ice of Devon Island, the ocean in Jones Sound, and the encompassing atmosphere. They are being carried out over a 3-year period under the leadership of Spencer Apollonio. The main effort is concentrated on attempts to evaluate such factors as physical, chemical, and biological variations in the arctic waters of Jones Sound caused by discharging glaciers; evaporation and transfer of moisture between the ocean waters and the ice-cap and glaciers; and the overall influences of solar radiation energy on the mass balance of the ice-cap, the biological production in the sea, and the growth and decay of sea-ice. Some supplementary studies in archaeology and geology are included in the expedition's work because of the marked deficiency of knowledge in those subjects for Devon Island. In the late summer of 1960 a main base was established on the north shore of Devon Island near Cape Skogn by an advance party of eight men taken in with their materials by the Canada Department of Transport icebreaker "d'Iberville". During a 3-week period buildings were erected and routes inland and to the ice-cap explored and marked, while an archaeological reconnaissance of the Cape Sparbo area was made by a small party under Mr. Gordon Lowther of McGill University. Everything was installed for a beginning of the 3-year program in April 1961. During the months of April to September 1961 21 men worked on extensive programs in geophysics, glaciology, marine biology and oceanography, meteorology, and surveying. Intensive work was also completed in archaeology and geology. ..

La démobilisation étudiante au Mexique : le double visage de la répression (juillet-décembre 1968)

Cet article est consacré à l’analyse de la mobilisation et démobilisation dans le cas du mouvement étudiant de 1968 dans la ville de Mexico. En partant d’un rappel du contexte où s’enracine la lutte et en suivant les échanges de coups entre protagonistes durant les sept mois du conflit, il s’intéresse au rôle de la répression dans le processus de mobilisation et démobilisation. En étudiant, d’une part, la dynamique interne du mouvement en lien avec la configuration sociopolitique qui la rend possible ou la limite et, d’autre part, des témoignages d’activistes afin de cerner la perception des coûts et des risques de la mobilisation, cet article souligne que le poids de la répression dans le cycle de protestation prend sens quand la répression est liée aux risques de la participation et à sa dimension émotionnelle dans une configuration spécifique.This article analyses the process of mobilization and demobilization in the case of the 1968 student movement in Mexico City. It begins with a reminder of the context in which the struggle is rooted, and goes on analyzing the fight between protagonists during seven months of conflict; it focuses on the role of repression in the process of mobilization and demobilization. By studying, on the one hand, the internal dynamics of the movement in relation to the socio-political configuration making possible or limiting this same dynamics, and, on the other, testimonies of activists to identify the perception of the mobilization’s costs and risks, this article highlights that the weight of repression in the protest cycle makes sense if linked to the costs and risks of participation and to the emotional dimension of repression in a specific configuration

La démobilisation étudiante au Mexique : le double visage de la répression (juillet-décembre 1968)

Cet article est consacré à l’analyse de la mobilisation et démobilisation dans le cas du mouvement étudiant de 1968 dans la ville de Mexico. En partant d’un rappel du contexte où s’enracine la lutte et en suivant les échanges de coups entre protagonistes durant les sept mois du conflit, il s’intéresse au rôle de la répression dans le processus de mobilisation et démobilisation. En étudiant, d’une part, la dynamique interne du mouvement en lien avec la configuration sociopolitique qui la rend possible ou la limite et, d’autre part, des témoignages d’activistes afin de cerner la perception des coûts et des risques de la mobilisation, cet article souligne que le poids de la répression dans le cycle de protestation prend sens quand la répression est liée aux risques de la participation et à sa dimension émotionnelle dans une configuration spécifique.This article analyses the process of mobilization and demobilization in the case of the 1968 student movement in Mexico City. It begins with a reminder of the context in which the struggle is rooted, and goes on analyzing the fight between protagonists during seven months of conflict; it focuses on the role of repression in the process of mobilization and demobilization. By studying, on the one hand, the internal dynamics of the movement in relation to the socio-political configuration making possible or limiting this same dynamics, and, on the other, testimonies of activists to identify the perception of the mobilization’s costs and risks, this article highlights that the weight of repression in the protest cycle makes sense if linked to the costs and risks of participation and to the emotional dimension of repression in a specific configuration

Crystal Structure of Human AKT1 with an Allosteric Inhibitor Reveals a New Mode of Kinase Inhibition

AKT1 (NP_005154.2) is a member of the serine/threonine AGC protein kinase family involved in cellular metabolism, growth, proliferation and survival. The three human AKT isozymes are highly homologous multi-domain proteins with both overlapping and distinct cellular functions. Dysregulation of the AKT pathway has been identified in multiple human cancers. Several clinical trials are in progress to test the efficacy of AKT pathway inhibitors in treating cancer. Recently, a series of AKT isozyme-selective allosteric inhibitors have been reported. They require the presence of both the pleckstrin-homology (PH) and kinase domains of AKT, but their binding mode has not yet been elucidated. We present here a 2.7 Å resolution co-crystal structure of human AKT1 containing both the PH and kinase domains with a selective allosteric inhibitor bound in the interface. The structure reveals the interactions between the PH and kinase domains, as well as the critical amino residues that mediate binding of the inhibitor to AKT1. Our work also reveals an intricate balance in the enzymatic regulation of AKT, where the PH domain appears to lock the kinase in an inactive conformation and the kinase domain disrupts the phospholipid binding site of the PH domain. This information advances our knowledge in AKT1 structure and regulation, thereby providing a structural foundation for interpreting the effects of different classes of AKT inhibitors and designing selective ones

Independent Ion Migration in Suspensions of Strongly Interacting Charged Colloidal Spheres

We report on sytematic measurements of the low frequency conductivity in aequous supensions of highly charged colloidal spheres. System preparation in a closed tubing system results in precisely controlled number densities between 1E16/m3 and 1E19/m^3 (packing fractions between 1E-7 and 1E-2) and electrolyte concentrations between 1E-7 and 1E-3 mol/l. Due to long ranged Coulomb repulsion some of the systems show a pronounced fluid or crystalline order. Under deionized conditions we find s to depend linearily on the packing fraction with no detectable influence of the phase transitions. Further at constant packing fraction s increases sublinearily with increasing number of dissociable surface groups N. As a function of c the conductivity shows pronounced differences depending on the kind of electrolyte used. We propose a simple yet powerful model based on independent migration of all species present and additivity of the respective conductivity contributions. It takes account of small ion macro-ion interactions in terms of an effectivly transported charge. The model successfully describes our qualitatively complex experimental observations. It further facilitates quantitative estimates of conductivity over a wide range of particle and experimental parameters.Comment: 32 pages, 17 figures, 2 tables, Accepted by Physical Review

Expression of Actin-interacting Protein 1 Suppresses Impaired Chemotaxis of Dictyostelium Cells Lacking the Na+-H+ Exchanger NHE1

Dictyostelium cells lacking the intracellular pH regulator NHE1 have defective chemotaxis. A modifier screen and reconstitution studies show expression of recombinant actin interacting protein 1 (Aip1) suppresses the Ddnhe1-phenotype. Aip1 promotes cofilin-dependent actin remodeling, which is likely a major determinant in pH-dependent chemotaxis

Metallation and mismetallation of iron and manganese proteins in vitro and in vivo: the class I ribonucleotide reductases as a case study

How cells ensure correct metallation of a given protein and whether a degree of promiscuity in metal binding has evolved are largely unanswered questions. In a classic case, iron- and manganese-dependent superoxide dismutases (SODs) catalyze the disproportionation of superoxide using highly similar protein scaffolds and nearly identical active sites. However, most of these enzymes are active with only one metal, although both metals can bind in vitro and in vivo. Iron(II) and manganese(II) bind weakly to most proteins and possess similar coordination preferences. Their distinct redox properties suggest that they are unlikely to be interchangeable in biological systems except when they function in Lewis acid catalytic roles, yet recent work suggests this is not always the case. This review summarizes the diversity of ways in which iron and manganese are substituted in similar or identical protein frameworks. As models, we discuss (1) enzymes, such as epimerases, thought to use Fe[superscript II] as a Lewis acid under normal growth conditions but which switch to Mn[superscript II] under oxidative stress; (2) extradiol dioxygenases, which have been found to use both Fe[superscript II] and Mn[superscript II], the redox role of which in catalysis remains to be elucidated; (3) SODs, which use redox chemistry and are generally metal-specific; and (4) the class I ribonucleotide reductases (RNRs), which have evolved unique biosynthetic pathways to control metallation. The primary focus is the class Ib RNRs, which can catalyze formation of a stable radical on a tyrosine residue in their β2 subunits using either a di-iron or a recently characterized dimanganese cofactor. The physiological roles of enzymes that can switch between iron and manganese cofactors are discussed, as are insights obtained from the studies of many groups regarding iron and manganese homeostasis and the divergent and convergent strategies organisms use for control of protein metallation. We propose that, in many of the systems discussed, “discrimination” between metals is not performed by the protein itself, but it is instead determined by the environment in which the protein is expressed.National Institutes of Health (U.S.) (Grant GM81393