365 research outputs found
An ancient spliceosomal intron in the ribosomal protein L7a gene (Rpl7a) of Giardia lamblia
BACKGROUND: Only one spliceosomal-type intron has previously been identified in the unicellular eukaryotic parasite, Giardia lamblia (a diplomonad). This intron is only 35 nucleotides in length and is unusual in possessing a non-canonical 5' intron boundary sequence, CT, instead of GT. RESULTS: We have identified a second spliceosomal-type intron in G. lamblia, in the ribosomal protein L7a gene (Rpl7a), that possesses a canonical GT 5' intron boundary sequence. A comparison of the two known Giardia intron sequences revealed extensive nucleotide identity at both the 5' and 3' intron boundaries, similar to the conserved sequence motifs recently identified at the boundaries of spliceosomal-type introns in Trichomonas vaginalis (a parabasalid). Based on these observations, we searched the partial G. lamblia genome sequence for these conserved features and identified a third spliceosomal intron, in an unassigned open reading frame. Our comprehensive analysis of the Rpl7a intron in other eukaryotic taxa demonstrates that it is evolutionarily conserved and is an ancient eukaryotic intron. CONCLUSION: An analysis of the phylogenetic distribution and properties of the Rpl7a intron suggests its utility as a phylogenetic marker to evaluate particular eukaryotic groupings. Additionally, analysis of the G. lamblia introns has provided further insight into some of the conserved and unique features possessed by the recently identified spliceosomal introns in related organisms such as T. vaginalis and Carpediemonas membranifera
A Family Showing No Evidence of Linkage Between the Ataxia Telangiectasia Gene and Chromosome
We have studied an inbred family in which two cousins presented with the same clinical features of ataxia telangiectasia (AT). Both patients are still ambulatory at ages 25 and 20. Cellular features of both patients are typical of AT and include increased radiosensitivity and an increased level of spontaneously occurring chromosome aberrations in peripheral blood lymphocytes. Linkage studies and haplotype analysis show no clear evidence that the gene for AT in this family is on chromosome 11q22-23. As previously reported AT families from complementation groups AB, C, and D have all shown linkage to this region of 11q22-23. Our study is of importance in suggesting additional locus heterogeneity
Exclusion limits on the WIMP-nucleon cross-section from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si
detectors to search for Weakly Interacting Massive Particles (WIMPs) via their
elastic-scattering interactions with nuclei while discriminating against
interactions of background particles. For recoil energies above 10 keV, events
due to background photons are rejected with >99.9% efficiency, and surface
events are rejected with >95% efficiency. The estimate of the background due to
neutrons is based primarily on the observation of multiple-scatter events that
should all be neutrons. Data selection is determined primarily by examining
calibration data and vetoed events. Resulting efficiencies should be accurate
to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed
fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent
with an earlier analysis with a more restrictive fiducial-volume cut.
Twenty-three WIMP candidate events are observed, but these events are
consistent with a background from neutrons in all ways tested. Resulting limits
on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude
unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}.
These limits border, but do not exclude, parameter space allowed by
supersymmetry models and accelerator constraints. Results are compatible with
some regions reported as allowed at 3-sigma by the annual-modulation
measurement of the DAMA collaboration. However, under the assumptions of
standard WIMP interactions and a standard halo, the results are incompatible
with the DAMA most likely value at >99.9% CL, and are incompatible with the
model-independent annual-modulation signal of DAMA at 99.99% CL in the
asymptotic limit.Comment: 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D;
v.2:clarified conclusions, added content and references based on referee's
and readers' comments; v.3: clarified introductory sections, added figure
based on referee's comment
Model-Independent Comparison of Direct vs. Indirect Detection of Supersymmetric Dark Matter
We compare the rate for elastic scattering of neutralinos from various nuclei
with the flux of upward muons induced by energetic neutrinos from neutralino
annihilation in the Sun and Earth. We consider both scalar and axial-vector
interactions of neutralinos with nuclei. We find that the event rate in a kg of
germanium is roughly equivalent to that in a - to -m muon
detector for a neutralino with primarily scalar coupling to nuclei. For an
axially coupled neutralino, the event rate in a 50-gram hydrogen detector is
roughly the same as that in a 10- to 500-m muon detector. Expected
experimental backgrounds favor forthcoming elastic-scattering detectors for
scalar couplings while the neutrino detectors have the advantage for
axial-vector couplings.Comment: 10 pages, self-unpacking uuencoded PostScript fil
Indirect Detection of a Light Higgsino Motivated by Collider Data
Kane and Wells recently argued that collider data point to a Higgsino-like
lightest supersymmetric partner which would explain the dark matter in our
Galactic halo. They discuss direct detection of such dark-matter particles in
laboratory detectors. Here, we argue that such a particle, if it is indeed the
dark matter, might alternatively be accessible in experiments which search for
energetic neutrinos from dark-matter annihilation in the Sun. We provide
accurate analytic estimates for the rates which take into account all relevant
physical effects. Currently, the predicted signal falls roughly one to three
orders of magnitude below experimental bounds, depending on the mass and
coupling of the particle; however, detectors such as MACRO, super-Kamiokande,
and AMANDA will continue to take data and should be able to rule out or confirm
an interesting portion of the possible mass range for such a dark-matter
particle within the next five years.Comment: 10 pages, RevTe
Nuclear Shell Model Calculations of Neutralino-Nucleus Cross Sections for Silicon 29 and Germanium 73
We present the results of detailed nuclear shell model calculations of the
spin-dependent elastic cross section for neutralinos scattering from \si29 and
\ge73. The calculations were performed in large model spaces which adequately
describe the configuration mixing in these two nuclei. As tests of the computed
nuclear wave functions, we have calculated several nuclear observables and
compared them with the measured values and found good agreement. In the limit
of zero momentum transfer, we find scattering matrix elements in agreement with
previous estimates for \si29 but significantly different than previous work for
\ge73. A modest quenching, in accord with shell model studies of other heavy
nuclei, has been included to bring agreement between the measured and
calculated values of the magnetic moment for \ge73. Even with this quenching,
the calculated scattering rate is roughly a factor of 2 higher than the best
previous estimates; without quenching, the rate is a factor of 4 higher. This
implies a higher sensitivity for germanium dark matter detectors. We also
investigate the role of finite momentum transfer upon the scattering response
for both nuclei and find that this can significantly change the expected rates.
We close with a brief discussion of the effects of some of the non-nuclear
uncertainties upon the matrix elements.Comment: 31 pages, figures avaiable on request, UCRL-JC-11408
Exclusion Limits on the WIMP-Nucleon Cross-Section from the First Run of the Cryogenic Dark Matter Search in the Soudan Underground Lab
The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si
detectors to seek Weakly Interacting Massive Particles (WIMPs) via their
elastic scattering interactions with nuclei. Simultaneous measurements of both
ionization and phonon energy provide discrimination against interactions of
background particles. For recoil energies above 10 keV, events due to
background photons are rejected with >99.99% efficiency. Electromagnetic events
very near the detector surface can mimic nuclear recoils because of reduced
charge collection, but these surface events are rejected with >96% efficiency
by using additional information from the phonon pulse shape. Efficient use of
active and passive shielding, combined with the the 2090 m.w.e. overburden at
the experimental site in the Soudan mine, makes the background from neutrons
negligible for this first exposure. All cuts are determined in a blind manner
from in situ calibrations with external radioactive sources without any prior
knowledge of the event distribution in the signal region. Resulting
efficiencies are known to ~10%. A single event with a recoil of 64 keV passes
all of the cuts and is consistent with the expected misidentification rate of
surface-electron recoils. Under the assumptions for a standard dark matter
halo, these data exclude previously unexplored parameter space for both
spin-independent and spin-dependent WIMP-nucleon elastic scattering. The
resulting limit on the spin-independent WIMP-nucleon elastic-scattering
cross-section has a minimum of 4x10^-43 cm^2 at a WIMP mass of 60 GeV/c^2. The
minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering
cross-section is 2x10^-37 cm^2 at a WIMP mass of 50 GeV/c^2.Comment: 37 pages, 42 figure
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