4,895 research outputs found
The ribosomal protein RACK1 is required for microRNA function in both C. elegans and humans
Despite the importance of microRNAs (miRNAs) in gene regulation, it is unclear how the miRNA-Argonaute complex-or miRNA-induced silencing complex (miRISC)-can regulate the translation of their targets in such diverse ways. We demonstrate here a direct interaction between the miRISC and the ribosome by showing that a constituent of the eukaryotic 40S subunit, receptor for activated C-kinase (RACK1), is important for miRNA-mediated gene regulation in animals. In vivo studies demonstrate that RACK1 interacts with components of the miRISC in nematodes and mammals. In both systems, the alteration of RACK1 expression alters miRNA function and impairs the association of the miRNA complex with the translating ribosomes. Our data indicate that RACK1 can contribute to the recruitment of miRISC to the site of translation, and support a post-initiation mode of miRNA-mediated gene repression. © 2011 European Molecular Biology Organization
Tests of the Las Campanas Distant Cluster Survey from Confirmation Observations for the ESO Distant Cluster Survey
The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic
study of the galaxy cluster population at two epochs, z~0.5 and z~0.8, drawn
from the Las Campanas Distant Cluster Survey (LCDCS). We report results from
the initial candidate confirmation stage of the program and use these results
to probe the properties of the LCDCS. Of the 30 candidates targeted, we find
statistically significant overdensities of red galaxies near 28. Of the ten
additional candidates serendipitously observed within the fields of the
targeted 30, we detect red galaxy overdensities near six. We test the
robustness of the published LCDCS estimated redshifts to misidentification of
the brighest cluster galaxy (BCG) in the survey data, and measure the spatial
alignment of the published cluster coordinates, the peak red galaxy
overdensity, and the brightest cluster galaxy. We conclude that for LCDCS
clusters out to z~0.8, 1) the LCDCS coordinates agree with the centroid of the
red galaxy overdensity to within 25'' (~150 h^{-1} kpc) for 34 out of 37
candidates with 3\sigma galaxy overdensities, 2) BCGs are typically coincident
with the centroid of the red galaxy population to within a projected separation
of 200 h^{-1} kpc (32 out of 34 confirmed candidates), 3) the red galaxy
population is strongly concentrated, and 4) the misidentification of the BCG in
the LCDCS causes a redshift error >0.1 in 15-20% of the LCDCS candidates. These
findings together help explain the success of the surface brightness
fluctuations detection method.Comment: 10 pages, 9 figures, accepted for publication in the November 10
issue of Ap
The Galaxy Populations of X-Ray Detected, Poor Groups
(Abridged) We determine the quantitative morphology and star formation
properties of galaxies in six nearby X-ray detected, poor groups using
multi-object spectroscopy and wide-field R imaging. We measure structural
parameters for each galaxy by fitting a PSF-convolved, two component model to
their surface brightness profiles. To compare directly the samples, we fade,
smooth, and rebin each galaxy image so that we effectively observe each galaxy
at the same redshift (9000 km/s) and physical resolution (0.87h^(-1) kpc). We
compare results for the groups to a sample of field galaxies. We find that: 1)
Galaxies spanning a wide range in morphological type and luminosity are
well-fit by a de Vaucouleurs bulge with exponential disk profile. 2)
Morphologically classifying these nearby group galaxies by their bulge fraction
(B/T) is fairly robust on average, even when their redshift has increased by up
to a factor of four and the effective resolution of the images is degraded by
up to a factor of five. 3) The fraction of bulge-dominated systems in these
groups is higher than in the field (~50% vs. ~20%). 4) The fraction of
bulge-dominated systems in groups decreases with increasing radius, similar to
the morphology-radius (~density) relation observed in galaxy clusters. 5)
Current star formation in group galaxies is correlated with significant
morphological asymmetry for disk-dominated systems (B/T<0.4). 6) The group
galaxies that are most disk-dominated (B/T<0.2) are less star forming and
asymmetric on average than their counterparts in the field.Comment: Accepted for publication in the Astrophysical Journal (26 pages + 12
figures); Figs 1 & 2 also available at
http://www.ucolick.org/~vy/astronomy/groups_figs.tar.g
The SBF Survey of Galaxy Distances. I. Sample Selection, Photometric Calibration, and the Hubble Constant
We describe a program of surface brightness fluctuation (SBF) measurements
for determining galaxy distances. This paper presents the photometric
calibration of our sample and of SBF in general. Basing our zero point on
observations of Cepheid variable stars, we find that the absolute SBF magnitude
in the Kron-Cousins I band correlates well with the mean (V-I)o color of a
galaxy according to
M_Ibar = (-1.74 +/- 0.07) + (4.5 +/- 0.25) [ (V-I)o - 1.15 ]
for 1.0 < (V-I) < 1.3. This agrees well with theoretical estimates from
stellar population models. Comparisons between SBF distances and a variety of
other estimators, including Cepheid variable stars, the Planetary Nebula
Luminosity Function (PNLF), Tully-Fisher (TF), Dn-sigma, SNII, and SNIa,
demonstrate that the calibration of SBF is universally valid and that SBF error
estimates are accurate. The zero point given by Cepheids, PNLF, TF (both
calibrated using Cepheids), and SNII is in units of Mpc; the zero point given
by TF (referenced to a distant frame), Dn-sigma and SNIa is in terms of a
Hubble expansion velocity expressed in km/s. Tying together these two zero
points yields a Hubble constant of H_0 = 81 +/- 6 km/s/Mpc. As part of this
analysis, we present SBF distances to 12 nearby groups of galaxies where
Cepheids, SNII, and SNIa have been observed.Comment: 29 pages plus 8 figures; LaTeX (AASTeX) uses aaspp4.sty (included);
To appear in The Astrophysical Journal, 1997 February 1 issue; Compressed
PostScript available from ftp://mars.tuc.noao.edu/sbf
Steady-State Contrast Response Functions Provide a Sensitive and Objective Index of Amblyopic Deficits
Purpose. Visual deficits in amblyopia are neural in origin, yet are difficult to characterize with functional magnetic resonance imagery (fMRI). Our aim was to develop an objective electroencephalography (EEG) paradigm that can be used to provide a clinically useful index of amblyopic deficits. Methods. We used steady-state visual evoked potentials (SSVEPs) to measure full contrast response functions in both amblyopic (n = 10, strabismic or mixed amblyopia, mean age: 44 years) and control (n = 5, mean age: 31 years) observers, both with and without a dichoptic mask. Results. At the highest target contrast, the ratio of amplitudes across the weaker and stronger eyes was highly correlated (r = 0.76) with the acuity ratio between the eyes. We also found that the contrast response function in the amblyopic eye had both a greatly reduced amplitude and a shallower slope, but that surprisingly dichoptic masking was weaker than in controls. The results were compared with the predictions of a computational model of amblyopia and suggest a modification to the model whereby excitatory (but not suppressive) signals are attenuated in the amblyopic eye. Conclusions. We suggest that SSVEPs offer a sensitive and objective measure of the ocular imbalance in amblyopia and could be used to assess the efficacy of amblyopia therapies currently under development
Recovering 3D structural properties of galaxies from SDSS-like photometry
Because of the 3D nature of galaxies, an algorithm for constructing spatial
density distribution models of galaxies on the basis of galaxy images has many
advantages over surface density distribution approximations. We present a
method for deriving spatial structure and overall parameters of galaxies from
images and estimate its accuracy and derived parameter degeneracies on a sample
of idealised model galaxies. The test galaxies consist of a disc-like component
and a spheroidal component with varying proportions and properties. Both
components are assumed to be axially symmetric and coplanar. We simulate these
test galaxies as if observed in the SDSS project through ugriz filters, thus
gaining a set of realistically imperfect images of galaxies with known
intrinsic properties. These artificial SDSS galaxies were thereafter remodelled
by approximating the surface brightness distribution with a 2D projection of a
bulge+disc spatial distribution model and the restored parameters were compared
to the initial ones. Down to the r-band limiting magnitude 18, errors of the
restored integral luminosities and colour indices remain within 0.05 mag and
errors of the luminosities of individual components within 0.2 mag. Accuracy of
the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and
becomes worse for galaxies with low B/D, but the general balance between bulges
and discs is not shifted systematically. Assuming that the intrinsic disc axial
ratio is < 0.3, the inclination angles can be estimated with errors < 5deg for
most of the galaxies with B/D < 2 and with errors < 15deg up to B/D = 6. Errors
of the recovered sizes of the galactic components are below 10% in most cases.
In general, models of disc components are more accurate than models of
spheroidal components for geometrical reasons.Comment: 15 pages, 13 figures, accepted for publication in RA
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