We demonstrate that reversible chemical reactions occur at TiO2/gas and CH3NH3PbI3/gas interfaces on a time scale of seconds to minutes. The chemisorption strongly affects their electronic ...properties, mainly acting to deplete TiO2 of free electrons and passivate surface traps on the perovskite. Although the chemistry is not directly probed, we infer that reversible chemistry occurs at the solid-state TiO2/CH3NH3PbI3 interface. Equilibrium or steady-state concentrations established for adsorbed species associated with each material would be voltage- and illumination-dependent due to free or photocarriers being a main reactant. Interfacial chemistry provides an additional physical mechanism to explain the origins of normal and anomalous hysteretic current–voltage characteristics of perovskite devices. Furthermore, chemical reactions help us to understand why measured perovskite ion-transport properties and the nature of hysteresis are highly dependent on interfaces.
The pentavalent organoarsenical arsinothricin (AST) is a natural product synthesized by the rhizosphere bacterium Burkholderia gladioli GSRB05. AST is a broad‐spectrum antibiotic effective against ...human pathogens such as carbapenem‐resistant Enterobacter cloacae. It is a non‐proteogenic amino acid and glutamate mimetic that inhibits bacterial glutamine synthetase. The AST biosynthetic pathway is composed of a three‐gene cluster, arsQML. ArsL catalyzes synthesis of reduced trivalent hydroxyarsinothricin (R‐AST‐OH), which is methylated by ArsM to the reduced trivalent form of AST (R‐AST). In the culture medium of B. gladioli, both trivalent species appear as the corresponding pentavalent arsenicals, likely due to oxidation in air. ArsQ is an efflux permease that is proposed to transport AST or related species out of the cells, but the chemical nature of the actual transport substrate is unclear. In this study, B. gladioli arsQ was expressed in Escherichia coli and shown to confer resistance to AST and its derivatives. Cells of E. coli accumulate R‐AST, and exponentially growing cells expressing arsQ take up less R‐AST. The cells exhibit little transport of their pentavalent forms. Transport was independent of cellular energy and appears to be equilibrative. A homology model of ArsQ suggests that Ser320 is in the substrate binding site. A S320A mutant exhibits reduced R‐AST‐OH transport, suggesting that it plays a role in ArsQ function. The ArsQ permease is proposed to be an energy‐independent uniporter responsible for downhill transport of the trivalent form of AST out of cells, which is oxidized extracellularly to the active form of the antibiotic.
The pentavalent organoarsenical arsinothricin (AST) synthesized by the rhizosphere bacterium Burkholderia gladioli GSRB05 is a broad‐spectrum antibiotic effective against human pathogens. B. gladioli ArsQ is an efflux permease responsible for downhill transport of the trivalent form of AST out of cells, which is oxidized extracellularly to the active form of the antibiotic.
Device physics A transistor fabricated from the crystalline phase of an organic semiconductor material could provide a path to improved switching speeds - rivalling those of devices built from ...inorganic materials such as silicon. The development of molecules and polymers with improved material properties has led to organic materials routinely overtaking amorphous silicon in terms of mobility, but the performance of organic field-effect transistors remains unsatisfactory for high-frequency applications. Julie Euvrard and Barry P. Rand are in the Department of Electrical and Computer Engineering and at the Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544, USA. e-mails: julie.euvrard@princeton.edu; brand@princeton.edu "The bottlenecks oforganic semiconductors determine the design ofdevices that are commercialized."
Habitat heterogeneity is a major structuring agent of ecological assemblages promoting beta diversity and ultimately contributing to overall higher global diversity. The exact processes by which ...heterogeneity increases diversity are scale dependent and encompass variation in other well-known processes, e.g., productivity, disturbance, and temperature. Thus, habitat heterogeneity likely triggers multiple and cascading diversity effects through ecological assemblages. Submarine canyons, a pervasive feature of the world's oceans, likely increase habitat heterogeneity at multiple spatial scales similar to their terrestrial analogues. However, our understanding of how processes regulating diversity, and the potential for cascading effects within these important topographic features, remains incomplete. Utilizing remote-operated vehicles (ROVs) for coring and video transects, we quantified faunal turnover in the deep-sea benthos at a rarely examined scale (1 m-1 km). Macrofaunal community structure, megafaunal density, carbon flux, and sediment characteristics were analyzed for the soft-bottom benthos at the base of cliff faces in Monterey Canyon (northeast Pacific Ocean) at three depths. We documented a remarkable degree of faunal turnover and changes in overall community structure at scales
<
100 m, and often
<
10 m, related to geographic features of a canyon complex. Ultimately, our findings indicated that multiple linked processes related to habitat heterogeneity, ecosystem engineering, and bottom-up dynamics are important to deep-sea biodiversity.
The carboxy-terminal binding protein (CtBP)-interacting protein (CtIP) is known to function in 5′ strand resection during homologous recombination, similar to the budding yeast Sae2 protein, but its ...role in this process is unclear. Here, we characterize recombinant human CtIP and find that it exhibits 5′ flap endonuclease activity on branched DNA structures, independent of the MRN complex. Phosphorylation of CtIP at known damage-dependent sites and other sites is essential for its catalytic activity, although the S327 and T847 phosphorylation sites are dispensable. A catalytic mutant of CtIP that is deficient in endonuclease activity exhibits wild-type levels of homologous recombination at restriction enzyme-generated breaks but is deficient in processing topoisomerase adducts and radiation-induced breaks in human cells, suggesting that the nuclease activity of CtIP is specifically required for the removal of DNA adducts at sites of DNA breaks.
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•Human CtIP exhibits 5′ flap endonuclease activity•Catalytic activity is dependent on phosphorylation•Resection of “clean” breaks does not require catalytic activity•Resection of ends with adducts requires catalytic activity
The human CtIP is important for resection of DNA double-strand break ends. Makharashvili et al. show that the human CtIP protein has a phosphorylation-dependent nuclease activity that is specifically required for efficient resection of double-strand breaks containing adducts.
Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox) has been used for decades as an antimicrobial growth promoter for poultry and swine. Roxarsone is excreted in chicken manure unchanged and can be ...microbially transformed into a variety of arsenic-containing compounds such as 3-amino-4-hydroxyphenylarsonic acid (HAPA(V)) that contaminate the environment and present a potential health hazard. To cope with arsenic toxicity, nearly every prokaryote has an ars (arsenic resistance) operon, some of which confer resistance to roxarsone. Pseudomonas putida KT2440 is a robust environmental isolate capable of metabolizing many aromatic compounds and is used as a model organism for biodegradation of aromatic compounds. Here we report that P. putida KT2440 (ΔΔars) in which the two ars operons had been deleted retains resistance to highly toxic trivalent Rox(III), the likely active form of roxarsone. In this study, a genomic library constructed from P. putida KT2440 (ΔΔars) was used to screen for resistance to Rox(III) in Escherichia coli. One gene, termed, PpnfnB, was identified that encodes a putative 6,7-dihydropteridine reductase. Cells expressing PpnfnB reduce the nitro group of Rox(III), and purified NfnB catalyzes FMN-NADPH-dependent nitroreduction of Rox(III) to less toxic HAPA(III). This identifies a key step in the breakdown of synthetic aromatic arsenicals.
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•A Pseudomonas putida strain with the ars operons deleted strain is resistant to highly toxic trivalent roxarsone (Rox(III))•Both wild type P. putida wild type and the ars deletion strains reduce Rox(III) to HAPA(III).•The PpnfnB gene from a genomic library of P. putida was identified by selection for Rox(III) resistance in E. coli.•The NfnB enzyme catalyzes FMN-NADPH-dependent nitroreduction, reducing Rox(III) to less toxic HAPA(III).•Niitroreduction is an alternative pathway for resistance to roxarsone
B cell progenitors require paracrine signals such as interleukin-7 (IL-7) provided by bone marrow stromal cells for proliferation and survival. Yet, how B cells regulate access to these signals in ...vivo remains unclear. Here we show that proB and IL-7
cells form a cell circuit wired by IL-7R signaling, which controls CXCR4 and focal adhesion kinase (FAK) expression and restricts proB cell movement due to increased adhesion to IL-7
CXCL12
cells. PreBCR signaling breaks this circuit by switching the preB cell behavior into a fast-moving and lower-adhesion state via increased CXCR4 and reduced FAK/α4β1 expression. This behavioral change reduces preB cell exposure to IL-7, thereby attenuating IL-7R signaling in vivo. Remarkably, IL-7 production is downregulated by signals provided by preB cells with unrepaired double-stranded DNA breaks and by preB acute lymphoblastic leukemic cells. Combined, these studies revealed that distinct cell circuits control the quality and homeostasis of B cell progenitors.
Background: Drinking water in multiple water districts in the Mid-Ohio Valley has been contaminated with perfluorooctanoic acid (PFOA), which was released by a nearby DuPont chemical plant. Two ...highly contaminated water districts began granular activated carbon filtration in 2007. Objectives: To determine the rate of decline in serum PFOA, and its corresponding half-life, during the first year after filtration. Methods: Up to six blood samples were collected from each of 200 participants from May 2007 until August 2008. The primary source of drinking water varied over time for some participants; our analyses were grouped according to water source at baseline in May—June 2007. Results: For Lubeck Public Service District customers, the average decrease in serum PFOA concentrations between May—June 2007 and May—August 2008 was 32 ng/mL (26%) for those primarily consuming public water at home (n = 130), and 16 ng/mL (28%) for those primarily consuming bottled water at home (n = 17). For Little Hocking Water Association customers, the average decrease in serum PFOA concentrations between November—December 2007 and May—June 2008 was 39 ng/mL (11%) for consumers of public water (n = 39) and 28 ng/mL (20%) for consumers of bottled water (n = 11). The covariate-adjusted average rate of decrease in serum PFOA concentration after water filtration was 26% per year (95% confidence interval, 25-28% per year). Conclusions: The observed data are consistent with first-order elimination and a median serum PFOA half-life of 2.3 years. Ongoing follow-up will lead to improved half-life estimation.
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