Ribonuclease Dicer belongs to the family of RNase III endoribonucleases, the enzymes that specifically hydrolyze phosphodiester bonds found in double-stranded regions of RNAs. Dicer enzymes are mostly known for their essential role in the biogenesis of small regulatory RNAs. A typical Dicer-type RNase consists of a helicase domain, a domain of unknown function (DUF283), a PAZ (Piwi-Argonaute-Zwille) domain, two RNase III domains, and a double-stranded RNA binding domain; however, the domain composition of Dicers varies among species. Dicer and its homologues developed only in eukaryotes; nevertheless, the two enzymatic domains of Dicer, helicase and RNase III, display high sequence similarity to their prokaryotic orthologs. Evolutionary studies indicate that a combination of the helicase and RNase III domains in a single protein is a eukaryotic signature and is supposed to be one of the critical events that triggered the consolidation of the eukaryotic RNA interference. In this review, we provide the genetic insight into the domain organization and structure of Dicer proteins found in vertebrate and invertebrate animals, plants and fungi. We also discuss, in the context of the individual domains, domain deletion variants and partner proteins, a variety of Dicers’ functions not only related to small RNA biogenesis pathways. 相似文献
The paper presents a theoretical analysis of stresses generated during convective drying of kaolin, based on elastic and viscoelastic models. The equations of these models were solved analytically for a cylindrically shaped sample; the distribution and evolution of the radial and circumferential stresses are illustrated in diagrams. The acoustic emission method was used in experimental tests for identification on line of the time period during which the stresses reach their maximal values. A better correlation has been found between the experimental tests and the theoretical predictions obtained on the basis of the viscoelastic model. 相似文献
The activity of NOx storage-reduction (NSR) catalysts is greatly reduced by sulfur poisoning, caused by the SO2 present in the exhaust stream. Desorption of sulfur species from poisoned NSR catalysts occurs at temperatures in excess of 600 °C using reducing atmospheres and conventional heating. In this work, microwave (MW) heating has been used to promote desulfurization of poisoned NSR catalysts. The experiments were carried out by heating the catalyst with MW radiation and using hydrogen as the reducing gas. Desorption of H2S at 200 °C was observed. Desorption at even lower temperatures (150 °C) was observed when water was introduced to the system. In the presence of water, sulfur species desorbed as both H2S and SO2. An overall reduction of sulfur species of about 60% was obtained. The use of MW heating proves to be an efficient way to achieve regeneration of poisoned NSR catalysts. 相似文献
Nos observations au secondaire et au collégial et les travaux menés sur la transition secondaire postsecondaire en mathématiques ont permis de documenter un ensemble de ruptures dans le passage d'un ordre à l'autre, soulignant l'importance de s'attarder à l'articulation entre ces deux ordres. C'est afin de mieux comprendre ces articulations possibles qu'une recherche collaborative a été menée avec des enseignants des deux ordres. L'analyse, puisant ses fondements en ethnométhodologie, fait apparaître l'utilisation du symbolisme comme un thème central de cette articulation interordres, et permet de retracer une trajectoire d'harmonisation qui se développe durant les rencontres en lien avec cette utilisation. 相似文献
A unique strain gauge based method is developed to identify the magnitude and location of a load on a slender beam with variable cross sections, and pinned, firm rest, soft rest, pinned‐fixed, and fixed boundary conditions. Four uniaxial strain gauges are mounted to the bottom surface of the beam, and the bending moment diagram of the beam can be constructed using measured strains on the beam. By combining individually scaled strain gauge outputs, the magnitude and location of the load can be accurately identified. The strain gauge based force transducer methodology is experimentally validated on prismatic beams with firm rest, soft rest, firm rest‐fixed, and fixed boundary conditions, and a continuously tapered beam with rest boundary conditions. The force transducer methodology is independent of the boundary conditions of the beam, and the error from strain gauge drift due to uniform thermal expansion on a prismatic beam can cancel out. 相似文献
Quenching and partitioning (Q&P) and a novel combined process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble®3S50 thermomechanical simulator. The heat treatments involved intercritical annealing at 800 °C and a two-step Q&P heat treatment with a partitioning time of 100 seconds at 400 °C. The “optimum” quench temperature of 318 °C was selected according to the constrained carbon equilibrium (CCE) criterion. The effects of high-temperature deformation (isothermal and non-isothermal) on the carbon enrichment of austenite, carbide formation, and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT) and scanning transmission electron microscopy (STEM). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples, it was significantly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the deformation-induced austenite-to-ferrite transformation (DIFT) phenomenon. By APT, the carbon accumulation at austenite/martensite interfaces was observed, with higher values for HSQ&P deformed isothermally (≈ 11 at. pct), when compared with non-isothermal HSQ&P (≈ 9.45 at. pct) and Q&P (≈ 7.6 at. pct). Moreover, a local Mn enrichment was observed in a ferrite/austenite interface, indicating ferrite growth under local equilibrium with negligible partitioning (LENP).
Listeria monocytogenes is a pathogen responsible for severe cases of food poisoning. Listeria spp. strains occurring in soil and water environments may serve as a reservoir of resistance determinants for pathogenic L. monocytogenes strains. A large collection of Listeria spp. strains (155) isolated from natural, agricultural, and urban areas was screened for resistance to heavy metals and metalloids, and the presence of resistance determinants and extrachromosomal replicons. Of the tested strains, 35% were resistant to cadmium and 17% to arsenic. Sequence analysis of resistance plasmids isolated from strains of Listeria seeligeri and Listeria ivanovii, and the chromosome of L. seeligeri strain Sr73, identified a novel variant of the cadAC cadmium resistance efflux system, cadA6, that was functional in L. monocytogenes cells. The cadA6 cassette was detected in four Listeria species, including strains of L. monocytogenes, isolated from various countries and sources—environmental, food-associated, and clinical samples. This resistance cassette is harbored by four novel composite or non-composite transposons, which increases its potential for horizontal transmission. Since some cadAC cassettes may influence virulence and biofilm formation, it is important to monitor their presence in Listeria spp. strains inhabiting different environments. 相似文献