1,117 research outputs found
A phylogenomic analysis of the Actinomycetales mce operons
BACKGROUND: The genome of Mycobacterium tuberculosis harbors four copies of a cluster of genes termed mce operons. Despite extensive research that has demonstrated the importance of these operons on infection outcome, their physiological function remains obscure. Expanding databases of complete microbial genome sequences facilitate a comparative genomic approach that can provide valuable insight into the role of uncharacterized proteins. RESULTS: The M. tuberculosis mce loci each include two yrbE and six mce genes, which have homology to ABC transporter permeases and substrate-binding proteins, respectively. Operons with an identical structure were identified in all Mycobacterium species examined, as well as in five other Actinomycetales genera. Some of the Actinomycetales mce operons include an mkl gene, which encodes an ATPase resembling those of ABC uptake transporters. The phylogenetic profile of Mkl orthologs exactly matched that of the Mce and YrbE proteins. Through topology and motif analyses of YrbE homologs, we identified a region within the penultimate cytoplasmic loop that may serve as the site of interaction with the putative cognate Mkl ATPase. Homologs of the exported proteins encoded adjacent to the M. tuberculosis mce operons were detected in a conserved chromosomal location downstream of the majority of Actinomycetales operons. Operons containing linked mkl, yrbE and mce genes, resembling the classic organization of an ABC importer, were found to be common in Gram-negative bacteria and appear to be associated with changes in properties of the cell surface. CONCLUSION: Evidence presented suggests that the mce operons of Actinomycetales species and related operons in Gram-negative bacteria encode a subfamily of ABC uptake transporters with a possible role in remodeling the cell envelope
The Infrared Surface Brightness Fluctuation Distances to the Hydra and Coma Clusters
We present IR surface brightness fluctuation (SBF) distance measurements to
NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster.
We explicitly corrected for the contributions to the fluctuations from globular
clusters, background galaxies, and residual background variance. We measured a
distance of 85 +/- 10 Mpc to NGC 4889 and a distance of 46 +/- 5 Mpc to the
Hydra cluster. Adopting recession velocities of 7186 +/- 428 km/s for Coma and
4054 +/- 296 km/s for Hydra gives a mean Hubble constant of H_0 = 87 +/- 11
km/s/Mpc. Corrections for residual variances were a significant fraction of the
SBF signal measured, and, if underestimated, would bias our measurement towards
smaller distances and larger values of H_0. Both NICMOS on the Hubble Space
Telescope and large-aperture ground-based telescopes with new IR detectors will
make accurate SBF distance measurements possible to 100 Mpc and beyond.Comment: 24 pages, 4 PostScript figures, 2 JPEG images; accepted for
publication in Ap
Constraints on the Space Density of Methane Dwarfs and the Substellar Mass Function from a Deep Near-Infrared Survey
We report preliminary results of a deep near-infrared search for
methane-absorbing brown dwarfs; almost five years after the discovery of Gl
229b, there are only a few confirmed examples of this type of object. New J
band, wide-field images, combined with pre-existing R band observations, allow
efficient identification of candidates by their extreme (R-J) colours.
Follow-up measurements with custom filters can then confirm objects with
methane absorption. To date, we have surveyed a total of 11.4 square degrees to
J~20.5 and R~25. Follow-up CH_4 filter observations of promising candidates in
1/4 of these fields have turned up no methane absorbing brown dwarfs. With 90%
confidence, this implies that the space density of objects similar to Gl 229b
is less than 0.012 per cubic parsec. These calculations account for the
vertical structure of the Galaxy, which can be important for sensitive
measurements. Combining published theoretical atmospheric models with our
observations sets an upper limit of alpha <= 0.8 for the exponent of the
initial mass function power law in this domain.Comment: 11 pages + 2 figures To be published in Astrophysical Journal Letter
Infrared Surface Brightness Fluctuations of the Coma Elliptical NGC 4874 and the Value of the Hubble Constant
We have used the Keck I Telescope to measure K-band surface brightness
fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma
cluster. We use deep HST WFPC2 optical imaging to account for the contamination
due to faint globular clusters and improved analysis techniques to derive
measurements of the SBF apparent magnitude. Using a new SBF calibration which
accounts for the dependence of K-band SBFs on the integrated color of the
stellar population, we measure a distance modulus of 34.99+/-0.21 mag (100+/-10
Mpc) for the Coma cluster. The resulting value of the Hubble constant is 71+/-8
km/s/Mpc, not including any systematic error in the HST Cepheid distance scale.Comment: ApJ Letters, in press. Uses emulateapj5.st
Genetic divergence among tomato leafminer populations based on AFLP analysis.
The objective of this work was to determine the genetic differences among eight Brazilian populations of the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), from the states of EspĂrito Santo (Santa Tereza), Goiás (Goianápolis), Minas Gerais (Uberlândia and Viçosa), Pernambuco (Camocim de SĂŁo FĂ©lix), Rio de Janeiro (SĂŁo JoĂŁo da Barra) and SĂŁo Paulo (PaulĂnia and SumarĂ©), using the amplified fragment length polymorphism (AFLP) technique. Fifteen combinations of EcoRI and MseI primers were used to assess divergence among populations. The data were analyzed using unweighted pair-group method, based on arithmetic averages (UPGMA) bootstrap analysis and principal coordinate analysis. Using a multilocus approach, these populations were divided in two groups, based on genetic fingerprints. Populations from Goianápolis, Santa Tereza, and Viçosa formed one group. Populations from Camocim de SĂŁo FĂ©lix, PaulĂnia, SĂŁo JoĂŁo da Barra, SumarĂ©, and Uberlândia fitted in the second group. These results were congruent with differences in susceptibility of this insect to insecticides, previously identified by other authors
Human monoclonal islet specific autoantibodies share features of islet cell and 64 kDa antibodies
The first human monoclonal islet cell antibodies of the IgG class (MICA 1-6) obtained from an individual with Type 1 (insulin-dependent) diabetes mellitus were cytoplasmic islet cell antibodies selected by the indirect immunofluorescence test on pancreas sections. Surprisingly, they all recognized the 64 kDa autoantigen glutamate decarboxylase. In this study we investigated which typical features of cytoplasmic islet cell antibodies are represented by these monoclonals. We show by double immunofluorescence testing that MICA 1-6 stain pancreatic beta cells which is in agreement with the beta-cell specific expression of glutamate decarboxylase. In contrast an islet-reactive IgM monoclonal antibody obtained from a pre-diabetic individual stained all islet cells but lacked the tissue specificity of MICA 1-6 and must therefore be considered as a polyreactive IgM-antibody. We further demonstrate that MICA 1-6 revealed typical features of epitope sensitivity to biochemical treatment of the target tissue which has been demonstrated for islet cell antibodies, and which has been used to argue for a lipid rather than a protein nature of target antigens. Our results provide direct evidence that the epitopes recognized by the MICA are destroyed by methanol/chloroform treatment but reveal a high stability to Pronase digestion compared to proinsulin epitopes. Conformational protein epitopes in glutamate decarboxylase therefore show a sensitivity to biochemical treatment of sections such as ganglioside epitopes. MICA 1-6 share typical features of islet cell and 64 kDa antibodies and reveal that glutamate decarboxylase-reactive islet cell antibodies represent a subgroup of islet cell antibodies present in islet cell antibody-positive sera
Infrared Photometry of the Globular Cluster Palomar 6
We present JHK photometry of Palomar 6. Our photometric measurements range
from the RGB-tip to 2 mag below the RHB and our CMDs show that Palomar~6
appears to have a well-defined RHB population. The distance modulus and
interstellar reddening of the cluster are estimated by comparing the magnitude
and color of Palomar 6 RHB stars with respect to those of 47 Tuc. We obtain
(m-M)_0 = 14.28 mag and E(B-V) = 1.30 mag for the cluster and our study
suggests that Palomar~6 is clearly located in the Galaxy's central regions. We
also discuss the metallicity of the cluster using the slope of the RGB. We
obtain [Fe/H] = -1.2 for Palomar~6 and our metallicity estimate is 0.5 - 1.0
dex lower than previous estimates by others.Comment: 14 pages, 4 tables, 12 figures; accepted for publication in AJ (2002
June
A parsec-scale outflow from the luminous YSO IRAS 17527-2439
Imaging observations of IRAS 17527-2439 are obtained in the near-IR JHK
photometric bands and in a narrow-band filter centred at the wavelength of the
H_2 1-0 S(1) line. The continuum-subtracted H_2 image is used to identify
outflows. The data obtained in this study are used in conjunction with Spitzer,
AKARI, and IRAS data. A parsec-scale bipolar outflow is discovered in our H_2
line image, which is supported by the detection in the archival Spitzer images.
The H_2 image exhibits signs of precession of the main jet and shows tentative
evidence for a second outflow. These suggest the possibility of a companion to
the outflow source. There is a strong component of continuum emission in the
direction of the outflow, which supports the idea that the outflow cavity
provides a path for radiation to escape, thereby reducing the radiation
pressure on the accreted matter. The bulk of the emission observed close to the
outflow in the WFCAM and Spitzer bands is rotated counter clockwise with
respect to the outflow traced in H_2, which may be due to precession. The YSO
driving the outflow is identified in the Spitzer images. The spectral energy
distribution (SED) of the YSO is studied using available radiative transfer
models. A model fit to the SED of the central source tells us that the YSO has
a mass of 12.23 M_sun and that it is in an early stage of evolution.Comment: 6 Pages, 5 figures, accepted for publication by Astronomy and
Astrophysic
Shortcuts in a Nonlinear Dynamical Braneworld in Six Dimensions
We consider a dynamical brane world in a six-dimensional spacetime containing
a singularity. Using the Israel conditions we study the motion of a 4-brane
embedded in this setup. We analyse the brane behaviour when its position is
perturbed about a fixed point and solve the full nonlinear dynamics in the
several possible scenarios. We also investigate the possible gravitational
shortcuts and calculate the delay between graviton and photon signals and the
ratio of the corresponding subtended horizons.Comment: 26 pages, 9 figures. References and discussion added. Title changed
to match the version accepted in Class. and Quant. Gra
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