1,721,199 research outputs found
Isolation of a cDNA encoding a Rab-related small GTP-binding protein (Accession No. AJ001367) from carrot cells
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Dihydrofolate reductase from Daucus carota cell suspension cultures: purification, molecular and kinetic characterization
No full textThe purification of dihydrofolate reductase (5, 6, 7, 8 tetrahydrofolate: NADP+ oxidoreductase, E.C.: 1.5.1.3) from Daucus carota to apparent homogeneity, is described. The enzyme is a soluble protein with a molecular weight of 183 000k +-2500, composed of identical subunits of 58 400+-1000. The enzyme is only
weakly recognized by antibodies against human DHFR. The carrot DHFR is characterized by a pH optimum of 5.9, Km values for dihydrofolate and NADPH of 3.7 μM and 2.2 μM, respectively and a turnover number of 4750 or 1500 when referring to the 183 K form or the 58 K monomer, respectively. Molecular and kinetic properties are remarkably different from those reported for the soybean enzyme. Sensitivity to methotrexate is similar to that of bacterial and mammalian enzymes while sensitivity to trimethoprim and dihydrotriazine is intermediate between the two groups of organisms
Studies on the intron-dependent meristematic expression of the dihydrofolate reductase/thymidylate synthase (DRTS) genes of Arabidopsis thaliana
No full textIn plants, dihydrofolate reductase (DHFR) and thymidylate synthase (TS) constitute a bifunctional enzyme (DRTS) which is essential for the synthesis of DNA precursors in proliferating or endoreduplicating cells. Previous characterizations of the three AtDRTS genes of Arabidopsis thaliana revealed distinctive patterns of expression and a crucial positive control of AtDRTS1 expression in apical meristems by an intragenic region containing the second intron of the gene [1]. In this study we report that the strong meristematic expression of AtDRTS2 is also strictly dependent on the first intron located in the 5’UTR of the gene. However, sequence comparisons of the first intron of AtDRTS2 and the second intron of AtDRTS1 could not detect common regions and a serial mutation analysis of the first AtDRTS2 intron could not identify regulatory elements enabling the meristematic activity of the gene. Nevertheless, the 5’UTR of AtDRTS2 is capable to confer strong meristematic expression when placed downstream of the AtDRS1 promoter suggesting an interchangeability between the two different introns and lack of specificity between promoter and intronic sequences. In addition, we found that the 5’UTR of AtDRTS2 acts at the transcriptional level and can confer meristematic activity also to the promoter of the AtBAM3 gene of A. thaliana, which is strongly and specifically expressed only in leaf tissues. This meristematic activating capacity, however, is not observed with a minimal 35S promoter which indicates that the first intron of AtDRTS2 cannot act autonomously as a promoter by itself but must interplay with additional regulatory regions
Field coverage and weed mapping by UAV swarms
Full text linkThe demands from precision agriculture (PA) for high-quality information at the individual plant level require to re-think the approaches exploited to date for remote sensing as performed by unmanned aerial vehicles (UAVs). A swarm of collaborating UAVs may prove more efficient and economically viable compared to other solutions. To identify the merits and limitations of a swarm intelligence approach to remote sensing, we propose here a decentralised multi-agent system for a field coverage and weed mapping problem, which is efficient, intrinsically robust and scalable to different group sizes. The proposed solution is based on a reinforced random walk with inhibition of return, where the information available from other agents (UAVs) is exploited to bias the individual motion pattern. Experiments are performed to demonstrate the efficiency and scalability of the proposed approach under a variety of experimental conditions, accounting also for limited communication range and different routing protocols. © 2017 IEEE
An Organ-On-A-Chip Engineered Platform to Study the Microbiota–Gut–Brain Axis in Neurodegeneration
No full textAfter decades of research, the etiology of neurodegenerative disorders such as Alzheimer's or Parkinson's disease is still mostly unknown. Recent findings indicate that the microorganisms in the human gut might be involved in neurodegenerative pathways. Here, we discuss an innovative groundbreaking bioengineering approach that could make a difference in this intriguing scenario
Transient dual porosity behavior for horizontal wells draining heterogeneous reservoirs.
No full textPaper of 71st Western Regional Meeting, Bakersfield (CA
Understanding the Role of Time-Varying Targets in Adaptive Distributed Area Coverage Control
No full textAmong the research community, interest is sparkling about the critical challenges of real-world applications where drones are deployed for tasks such as surveillance, environmental monitoring, and search-and-rescue missions. Within this context, coverage control can be seen as a basic behavior, a building block for complex and dynamic missions. Oftentimes, the environment is inherently dynamic, with variable points of interest subject to fluctuations in their importance and distribution. Additionally, the configuration of the drone fleet, including the number and positions of drones, may vary due to logistical constraints or mission-specific requirements. This experimental article presents the results of a comprehensive study focusing on a novel coverage algorithm based on Voronoi diagrams in the context of drone deployment. The primary objective is to empirically demonstrate the robustness of the proposed algorithm in real settings and dynamically changing environment with varying drone configurations. To substantiate our approach’s efficacy, we conducted an experimental study encompassing an extensive set of simulations, which were assessed using a predefined set of metrics. At the same time, the algorithm has been field tested employing a fleet of quad-copters in a series of proof-of-concept experiments that involved the deployment of up to seven aerial units
Selection of methotrexate-resistant cell lines in Daucus carota: biochemical analysis and genetic characterization by protoplast fusion
No full textIn this work we report the isolation and characterization of carrot cell lines resistant to methotrexate (Mtx). Selection of spontaneous variants was accomplished by one step and two step exposure to Mtx. Among lines that showed normal Mtx uptake, no difference from the parental line was found in inactivation of the inhibitor or affinity of dihydrofolate reductase (DHFR) for Mtx.
One step resistant lines, when maintained in a medium lacking Mtx for at least 75 days, showed a DHFR specific activity and capacity to bind Mtx 3 -4 times that of the parental one and these values remained stable up to 6 months. DHFR activity appeared to be very low in cell lines grown with Mtx, due to the presence of an inhibitor, possibly Mtx itself, in the cell extract.
Nevertheless, measurement of the amount of DHFR using antibodies to the pure enzyme indicated that the level of the enzyme is about the same in lines maintained either in the presence or in the absence of Mtx. Genetic analysis by protoplast fusion has shown that resistance is a dominant or semidominant trait
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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