Cell Cycle-Dependent Induction of Homologous Recombination by a Tightly Regulated I-SceI Fusion Protein

Double-strand break repair is executed by two major repair pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). Whereas NHEJ contributes to the repair of ionizing radiation (IR)-induced double strand breaks (DSBs) throughout the cell cycle, HR acts predominantly during the S and G2 phases of the cell cycle. The rare-cutting restriction endonuclease, I-SceI, is in common use to study the repair of site-specific chromosomal DSBs in vertebrate cells. To facilitate analysis of I-SceI-induced DSB repair, we have developed a stably expressed I-SceI fusion protein that enables precise temporal control of I-SceI activation, and correspondingly tight control of the timing of onset of site-specific chromosome breakage. I-SceI-induced HR showed a strong, positive linear correlation with the percentage of cells in S phase, and was negatively correlated with the G1 fraction. Acute depletion of BRCA1, a key regulator of HR, disrupted the relationship between S phase fraction and I-SceI-induced HR, consistent with the hypothesis that BRCA1 regulates HR during S phase

Optimal siting, sizing, and enforcement of marine protected areas

The design of protected areas, whether marine or terrestrial, rarely considers how people respond to the imposition of no-take sites with complete or incomplete enforcement. Consequently, these protected areas may fail to achieve their intended goal. We present and solve a spatial bio-economic model in which a manager chooses the optimal location, size, and enforcement level of a marine protected area (MPA). This manager acts as a Stackelberg leader, and her choices consider villagers’ best response to the MPA in a spatial Nash equilibrium of fishing site and effort decisions. Relevant to lower income country settings but general to other settings, we incorporate limited enforcement budgets, distance costs of traveling to fishing sites, and labor allocation to onshore wage opportunities. The optimal MPA varies markedly across alternative manager goals and budget sizes, but always induce changes in villagers’ decisions as a function of distance, dispersal, and wage. We consider MPA managers with ecological conservation goals and with economic goals, and identify the shortcomings of several common manager decision rules, including those focused on: (1) fishery outcomes rather than broader economic goals, (2) fish stocks at MPA sites rather than across the full marinescape, (3) absolute levels rather than additional values, and (4) costless enforcement. Our results demonstrate that such naïve or overly narrow decision rules can lead to inefficient MPA designs that miss economic and conservation opportunities

Étude de la recombinaison en volume des électrons avec les trous piégés, dans le cristal d'anthracène

The recombination of free electrons with holes trapped on a localized impurity level (detrapping time 140 ms, 300 oK) is coulombic. The measured recombination rate constant is Re = 2.2 ± 0.2 × 10-7 cm3 s-1 with the electric field along c', in order of magnitude agreement with the Langevin formula. The difference could be due to a small distortion of the crystal, or of the energy bands, in the vicinity of the impurity. The analysis of the results shows that some previously given values of R (free-free) are too high, due to non-consideration of electrostatic effects. The method allows in principle the measurement of the spatial distribution of the trapped holes.La recombinaison des électrons libres avec les trous piégés sur un niveau d'impureté (temps de séjour à 300 °K : 140 ms) est coulombienne. La constante de vitesse correspondante est Re = 2,2 ± 0,2 × 10 -7 cm3 s-1 lorsque le champ est appliqué dans la direction c'. Cette valeur est du même ordre de grandeur mais plus petite d'un facteur 3 que celle donnée par Re = 4π qui exprime la constante de vitesse de recombinaison coulombienne dans un tel milieu. L'effet de canalisation par le champ électrique est insuffisant pour expliquer cette différence, qui peut être due à une déformation du cristal ou des bandes d'énergie, au voisinage de l'impureté. L'analyse quantitative des expériences montre que plusieurs mesures antérieures de la constante de recombinaison des porteurs libres R donnent des valeurs trop fortes de 100 % environ, faute de tenir compte de l'interaction électrostatique entre les distributions volumiques de charges positives et négatives. La méthode utilisée permet en principe de déterminer sous certaines conditions la distribution spatiale de trous piégés dans un cristal

Interaction of triplet excitons with trapped and free holes in crystalline anthracene. Exciton quenching, current enhancement and magnetic field effects

The effect of interaction between free triplet excitons and free or (mainly) trapped holes is studied in crystalline anthracene, both on the triplet lifetime and the detrapping of holes. The rate constant of the triplet-hole interaction is R = (5.5 ± 2) 10^-12 cm3 s-1 for trapped holes and R' = (2 ± 1) 10^-9 cm3 s-1 for free holes; these values are comparable to those expected for diffusion limited processes, by triplet and hole diffusivity respectively. The efficiency of detrapping by triplets is large ≳ 0.1. The effect of a magnetic field on the photocurrent is investigated, as a function of intensity and orientation of the field. A model for the triplet-doublet interaction similar to that for the triplet-triplet interaction, where triplet-doublet pairs formation is considered, is used to calculate the rate constants for pair formation (4 × 10^-11 cm3 s-1) separation (2 x 10^8 s-1) and reaction (3 x 10^7 s-1). The values of the parameters D and E of the triplet exciton may be determined too. The study of the variation of the effect with the applied voltage shows evidence of the importance of free holes.On étudie l'effet de l'interaction entre excitons triplets libres et trous libres ou (principalement) piégés dans le cristal d'anthracène, à la fois sur la durée de vie des triplets et sur le dépiégeage des trous. On détermine les constantes de vitesse d'interaction des triplets avec les trous piégés R = (5,5 ± 2) 10^-12 cm3 s -1 et les trous libres R' = (2 ± 1).10^-9 cm3 s-1, valeurs proches de celles qu'on prévoit pour des processus limités par la diffusion des triplets et des trous respectivement. On trouve que l'efficacité du dépiégeage par les triplets est élevée ≳ 0,1. On analyse ensuite l'effet d'un champ magnétique sur le photocourant en fonction de l'intensité et de la direction de ce champ. Un modèle de l'interaction triplet-triplet, où l'on considère la formation de paires TD rend compte des observations et permet de calculer des constantes de vitesse pour la formation de ces paires (4 × 10^-11 cm 3 s-1), leur séparation (2 × 10^8 s-1) et leur réaction (3 x 10^7 s-1). On peut également ainsi retrouver les valeurs des paramètres D et E de l'exciton triplet. L'étude de la variation de cet effet avec la tension met en évidence l'importance des trous libres

Strong transparency required for carbon credit mechanisms

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this recordThe credibility of carbon offset mechanisms is threatened by many issues related to their true effectiveness. We advocate that these issues cannot be effectively addressed without a dramatic improvement in transparency across the entire value chain of carbon offsetting, a crucial step for achieving a reduction in carbon emissions.Natural Environment Research Council (NERC

Strong transparency required for carbon credit mechanisms

The credibility of carbon offset mechanisms is threatened by many issues related to their true effectiveness. We advocate that these issues cannot be effectively addressed without a dramatic improvement in transparency across the entire value chain of carbon offsetting, a crucial step for achieving a reduction in carbon emissions