12,216 research outputs found
Core genome components and lineage specific expansions in malaria parasites Plasmodium
<p>Abstract</p> <p>Background</p> <p>The increasing resistance of <it>Plasmodium,</it> the malaria parasites, to multiple commonly used drugs has underscored the urgent need to develop effective antimalarial drugs and vaccines. The new direction of genomics-driven target discovery has become possible with the completion of parasite genome sequencing, which can lead us to a better understanding of how the parasites develop the genetic variability that is associated with their response to environmental challenges and other adaptive phenotypes.</p> <p>Results</p> <p>We present the results of a comprehensive analysis of the genomes of six <it>Plasmodium</it> species, including two species that infect humans, one that infects monkeys, and three that infect rodents. The core genome shared by all six species is composed of 3,351 genes, which make up about 22%-65% of the genome repertoire. These components play important roles in fundamental functions as well as in parasite-specific activities. We further investigated the distribution and features of genes that have been expanded in specific Plasmodium lineage(s). Abundant duplicate genes are present in the six species, with 5%-9% of the whole genomes composed lineage specific radiations. The majority of these gene families are hypothetical proteins with unknown functions; a few may have predicted roles such as antigenic variation.</p> <p>Conclusions</p> <p>The core genome components in the malaria parasites have functions ranging from fundamental biological processes to roles in the complex networks that sustain the parasite-specific lifestyles appropriate to different hosts. They represent the minimum requirement to maintain a successful life cycle that spans vertebrate hosts and mosquito vectors. Lineage specific expansions (LSEs) have given rise to abundant gene families in <it>Plasmodium.</it> Although the functions of most families remain unknown, these LSEs could reveal components in parasite networks that, by their enhanced genetic variability, can contribute to pathogenesis, virulence, responses to environmental challenges, or interesting phenotypes.</p
Charmless Two-body decays In Soft-Collinear-Effective-Theory
We provide the analysis of charmless two-body decays under the
framework of the soft-collinear-effective-theory (SCET), where denotes a
light vector (pseudoscalar) meson. Besides the leading power contributions,
some power corrections (chiraly enhanced penguins) are also taken into account.
Using the current available and experimental data on
branching fractions and CP asymmetry variables, we find two kinds of solutions
in fit for the 16 non-perturbative inputs which are essential in the
87 and decay channels. Chiraly enhanced penguins can change
several charming penguins sizably, since they share the same topology. However,
most of the other non-perturbative inputs and predictions on branching ratios
and CP asymmetries are not changed too much. With the two sets of inputs, we
predict the branching fractions and CP asymmetries of other modes especially
decays. The agreements and differences with results in QCD
factorization and perturbative QCD approach are analyzed. We also study the
time-dependent CP asymmetries in channels with CP eigenstates in the final
states and some other channels such as and
. In the perturbative QCD approach, the
penguins in annihilation diagrams play an important role. Although
they have the same topology with charming penguins in SCET, there are many
differences between the two objects in weak phases, magnitudes, strong phases
and factorization properties.Comment: 34 pages, revtex, 2 figures, published at PR
Diquarks and the Semi-Leptonic Decay of in the Hybrid Scheme
In this work we use the heavy-quark-light-diquark picture to study the
semileptonic decay in the so-called
hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for
larger (corresponding to small recoil), which is the invariant mass
square of , whereas the perturbative QCD approach for smaller
to calculate the form factors. The turning point where we require the form
factors derived in the two approaches to be connected, is chosen near
. It is noted that the kinematic parameter which is
usually adopted in the perturbative QCD approach, is in fact exactly the same
as the recoil factor used in HQET where , are the
four velocities of and respectively. We find that the
final result is not much sensitive to the choice, so that it is relatively
reliable. Moreover, we apply a proper numerical program within a small range
around to make the connection sufficiently smooth and we
parameterize the form factor by fitting the curve gained in the hybrid scheme.
The expression and involved parameters can be compared with the ones gained by
fitting the experimental data. In this scheme the end-point singularities do
not appear at all. The calculated value is satisfactorily consistent with the
data which is recently measured by the DELPHI collaboration within two standard
deviations.Comment: 16 pages, including 4 figures, revtex
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