582 research outputs found
Improvement of Forage Quality by Means of Biotechnology: Stable Transformation of Warm-Season Grasses by Particle Bombardment
We have used a simple and inexpensive, self-built particle acceleration apparatus for direct delivery of DNA to cultured cells of warm-season grasses. High levels of transient expression of the b-glucuronidase gene were obtained following bombardment of embryogenic suspension cells and calli of bahiagrass (Paspalum notatum FlĂĽgge) and dallisgrass (Paspalum dilatatum Poir). Furthermore, stable transformed calli of both species have been obtained using this simple particle gun
Transformation in Lotus Corniculatus: Towards Low-Lignin Pasture Through Antisense RNA
We have developed a rapid and reproducible transformation system for bird’s-foot trefoil (Lotus corniculatus L.) by using Agrobacterium-mediated T-DNA transfer and the incorporation of the antisense gene for cinnamyl alcohol dehydrogenase (CAD) from Aralia cordata into Lotus for lignin reduction. The presence of the transferred antisense gene in regenerated plants has been confirmed by PCR analysis
Why highly expressed proteins evolve slowly
Much recent work has explored molecular and population-genetic constraints on
the rate of protein sequence evolution. The best predictor of evolutionary rate
is expression level, for reasons which have remained unexplained. Here, we
hypothesize that selection to reduce the burden of protein misfolding will
favor protein sequences with increased robustness to translational missense
errors. Pressure for translational robustness increases with expression level
and constrains sequence evolution. Using several sequenced yeast genomes,
global expression and protein abundance data, and sets of paralogs traceable to
an ancient whole-genome duplication in yeast, we rule out several confounding
effects and show that expression level explains roughly half the variation in
Saccharomyces cerevisiae protein evolutionary rates. We examine causes for
expression's dominant role and find that genome-wide tests favor the
translational robustness explanation over existing hypotheses that invoke
constraints on function or translational efficiency. Our results suggest that
proteins evolve at rates largely unrelated to their functions, and can explain
why highly expressed proteins evolve slowly across the tree of life.Comment: 40 pages, 3 figures, with supporting informatio
A Comprehensive Framework for Human Resources for Health System Development in Fragile and Post-Conflict States
Noriko Fujita and colleagues offer a comprehensive framework for human resource system development, based upon experiences in three fragile and post-conflict health systems: Afghanistan, the Democratic Republic of Congo, and Cambodia
Development of a 66 kV-5 kA Class HTS Power Cable with IBAD/PLD REBCO Tapes
AbstractHigh temperature superconducting (HTS) cables are able to achieve large power capacity and low-loss power transmission. In the Japanese national project, Fujikura Ltd. worked on developing a 66 kV-5 kArms HTS power cable using high critical current (Ic) REBa2Cu3Ox (REBCO, RE = rare earth) tapes. One of the technical targets in this project is to reduce AC loss to less than 2W/m at 5 kArms. The REBCO tapes with 240 A/4mm-width of Ic at 77K, self field, which were fabricated by Ion-beam-assisted-deposition (IBAD) and Pulsed Laser Deposition (PLD) method, were applied to a HTS power cable in order to achieve extremely low AC loss. As a result, we have succeeded in developing a 20 m-long 66 kV-5 kArms HTS power cable. The measured AC loss was achieved 1.4W/m at 77K and 1.0W/m at 67K at 5 kArms
Amplified biochemical oscillations in cellular systems
We describe a mechanism for pronounced biochemical oscillations, relevant to
microscopic systems, such as the intracellular environment. This mechanism
operates for reaction schemes which, when modeled using deterministic rate
equations, fail to exhibit oscillations for any values of rate constants. The
mechanism relies on amplification of the underlying stochasticity of reaction
kinetics within a narrow window of frequencies. This amplification allows
fluctuations to beat the central limit theorem, having a dominant effect even
though the number of molecules in the system is relatively large. The mechanism
is quantitatively studied within simple models of self-regulatory gene
expression, and glycolytic oscillations.Comment: 35 pages, 6 figure
From Bipolar to Elliptical: Simulating the Morphological Evolution of Planetary Nebulae
The majority of Proto-planetary nebulae (PPN) are observed to have bipolar
morphologies. The majority of mature PN are observed to have elliptical shapes.
In this paper we address the evolution of PPN/PN morphologies attempting to
understand if a transition from strongly bipolar to elliptical shape can be
driven by changes in the parameters of the mass loss process. To this end we
present 2.5D hydrodynamical simulations of mass loss at the end stages of
stellar evolution for intermediate mass stars. We track changes in wind
velocity, mass loss rate and mass loss geometry. In particular we focus on the
transition from mass loss dominated by a short duration jet flow (driven during
the PPN phase) to mass loss driven by a spherical fast wind (produced by the
central star of the PN). We address how such changes in outflow characteristics
can change the nebula from a bipolar to an elliptical morphology. Our results
show that including a period of jet formation in the temporal sequence of PPN
to PN produces realistic nebular synthetic emission geometries. More
importantly such a sequence provides insight, in principle, into the apparent
difference in morphology statistics characterizing PPN and PN systems. In
particular we find that while jet driven PPN can be expected to be dominated by
bipolar morphologies, systems that begin with a jet but are followed by a
spherical fast wind will evolve into elliptical nebulae. Furthermore, we find
that spherical nebulae are highly unlikely to ever derive from either bipolar
PPN or elliptical PN.Comment: Accepted for publication in the MNRAS, 15 pages, 7 figure
Atypical presentation of "takotsubo cardiomyopathy" without ST segment elevation: a case report
Signatures of arithmetic simplicity in metabolic network architecture
Metabolic networks perform some of the most fundamental functions in living
cells, including energy transduction and building block biosynthesis. While
these are the best characterized networks in living systems, understanding
their evolutionary history and complex wiring constitutes one of the most
fascinating open questions in biology, intimately related to the enigma of
life's origin itself. Is the evolution of metabolism subject to general
principles, beyond the unpredictable accumulation of multiple historical
accidents? Here we search for such principles by applying to an artificial
chemical universe some of the methodologies developed for the study of genome
scale models of cellular metabolism. In particular, we use metabolic flux
constraint-based models to exhaustively search for artificial chemistry
pathways that can optimally perform an array of elementary metabolic functions.
Despite the simplicity of the model employed, we find that the ensuing pathways
display a surprisingly rich set of properties, including the existence of
autocatalytic cycles and hierarchical modules, the appearance of universally
preferable metabolites and reactions, and a logarithmic trend of pathway length
as a function of input/output molecule size. Some of these properties can be
derived analytically, borrowing methods previously used in cryptography. In
addition, by mapping biochemical networks onto a simplified carbon atom
reaction backbone, we find that several of the properties predicted by the
artificial chemistry model hold for real metabolic networks. These findings
suggest that optimality principles and arithmetic simplicity might lie beneath
some aspects of biochemical complexity
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