184 research outputs found
Equine Rhinitis A Virus and Its Low pH Empty Particle: Clues Towards an Aphthovirus Entry Mechanism?
Equine rhinitis A virus (ERAV) is closely related to foot-and-mouth disease virus (FMDV), belonging to the genus Aphthovirus of the Picornaviridae. How picornaviruses introduce their RNA genome into the cytoplasm of the host cell to initiate replication is unclear since they have no lipid envelope to facilitate fusion with cellular membranes. It has been thought that the dissociation of the FMDV particle into pentameric subunits at acidic pH is the mechanism for genome release during cell entry, but this raises the problem of how transfer across the endosome membrane of the genome might be facilitated. In contrast, most other picornaviruses form ‘altered’ particle intermediates (not reported for aphthoviruses) thought to induce membrane pores through which the genome can be transferred. Here we show that ERAV, like FMDV, dissociates into pentamers at mildly acidic pH but demonstrate that dissociation is preceded by the transient formation of empty 80S particles which have released their genome and may represent novel biologically relevant intermediates in the aphthovirus cell entry process. The crystal structures of the native ERAV virus and a low pH form have been determined via highly efficient crystallization and data collection strategies, required due to low virus yields. ERAV is closely similar to FMDV for VP2, VP3 and part of VP4 but VP1 diverges, to give a particle with a pitted surface, as seen in cardioviruses. The low pH particle has internal structure consistent with it representing a pre-dissociation cell entry intermediate. These results suggest a unified mechanism of picornavirus cell entry
New penicillin-producing Penicillium species and an overview of section Chrysogena
Species classified in Penicillium sect. Chrysogena are primary soil-borne and the most well-known members are P. chrysogenum and P. nalgiovense. Penicillium chrysogenum has received much attention because of its role in the production on penicillin and as a contaminant of indoor environments and various food and feedstuffs. Another biotechnologically important species is P. nalgiovense, which is used as a fungal starter culture for the production of fermented meat products. Previous taxonomic studies often had conflicting species circumscriptions. Here, we present a multigene analysis, combined with phenotypic characters and extrolite data, demonstrating that sect. Chrysogena consists of 18 species. Six of these are newly described here (P. allii-sativi, P. desertorum, P. goetzii, P. halotolerans, P. tardochrysogenum, P. vanluykii) and P. lanoscoeruleum was found to be an older name for P. aethiopicum. Each species produces a unique extrolite profile. The species share phenotypic characters, such as good growth on CYA supplemented with 5 % NaCl, ter- or quarterverticillate branched conidiophores and short, ampulliform phialides (<9 μm). Conidial colours, production of ascomata and ascospores, shape and ornamentation of conidia and growth rates on other agar media are valuable for species identification. Eight species (P. allii-sativi, P. chrysogenum, P. dipodomyis, P. flavigenum, P. nalgiovense, P. rubens, P. tardochrysogenum and P. vanluykii) produce penicillin in culture
Kohler's disease: An unusual cause for a limping child
Kohler's disease: an unusual cause for a limping chil
The Science Case for the Planet Formation Imager (PFI)
Among the most fascinating and hotly-debated areas in contemporary
astrophysics are the means by which planetary systems are assembled from the
large rotating disks of gas and dust which attend a stellar birth. Although
important work has already been, and is still being done both in theory and
observation, a full understanding of the physics of planet formation can only
be achieved by opening observational windows able to directly witness the
process in action. The key requirement is then to probe planet-forming systems
at the natural spatial scales over which material is being assembled. By
definition, this is the so-called Hill Sphere which delineates the region of
influence of a gravitating body within its surrounding environment. The Planet
Formation Imager project (PFI) has crystallized around this challenging goal:
to deliver resolved images of Hill-Sphere-sized structures within candidate
planet-hosting disks in the nearest star-forming regions. In this contribution
we outline the primary science case of PFI. For this purpose, we briefly review
our knowledge about the planet-formation process and discuss recent
observational results that have been obtained on the class of transition disks.
Spectro-photometric and multi-wavelength interferometric studies of these
systems revealed the presence of extended gaps and complex density
inhomogeneities that might be triggered by orbiting planets. We present
detailed 3-D radiation-hydrodynamic simulations of disks with single and
multiple embedded planets, from which we compute synthetic images at
near-infrared, mid-infrared, far-infrared, and sub-millimeter wavelengths,
enabling a direct comparison of the signatures that are detectable with PFI and
complementary facilities such as ALMA. From these simulations, we derive some
preliminary specifications that will guide the array design and technology
roadmap of the facility.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, Paper ID 9146-120, 13 pages, 3 Figure
The last gasps of VY CMa: Aperture synthesis and adaptive optics imagery
We present new observations of the red supergiant VY CMa at 1.25 micron, 1.65
micron, 2.26 micron, 3.08 micron and 4.8 micron. Two complementary
observational techniques were utilized: non-redundant aperture masking on the
10-m Keck-I telescope yielding images of the innermost regions at unprecedented
resolution, and adaptive optics imaging on the ESO 3.6-m telescope at La Silla
attaining extremely high (~10^5) peak-to-noise dynamic range over a wide field.
For the first time the inner dust shell has been resolved in the near-infrared
to reveal a one-sided extension of circumstellar emission within 0.1" (~15
R_star) of the star. The line-of-sight optical depths of the circumstellar dust
shell at 1.65 micron, 2.26 micron, and 3.08 micron have been estimated to be
1.86 +/- 0.42, 0.85 +/- 0.20, and 0.44 +/- 0.11. These new results allow the
bolometric luminosity of VY~CMa to be estimated independent of the dust shell
geometry, yielding L_star ~ 2x10^5 L_sun. A variety of dust condensations,
including a large scattering plume and a bow-shaped dust feature, were observed
in the faint, extended nebula up to 4" from the central source. While the
origin of the nebulous plume remains uncertain, a geometrical model is
developed assuming the plume is produced by radially-driven dust grains forming
at a rotating flow insertion point with a rotational period between 1200-4200
years, which is perhaps the stellar rotational period or the orbital period of
an unseen companion.Comment: 25 pages total with 1 table and 5 figures. Accepted by Astrophysical
Journal (to appear in February 1999
FMDV replicons encoding green fluorescent protein are replication competent
The study of replication of viruses that require high bio-secure facilities can be accomplished with less stringent containment using non-infectious 'replicon' systems. The FMDV replicon system (pT7rep) reported by Mclnerney et al. (2000) was modified by the replacement of sequences encoding chloramphenicol acetyl-transferase (CAT) with those encoding a functional L proteinase (Lpro) linked to a bi-functional fluorescent/antibiotic resistance fusion protein (green fluorescent protein/puromycin resistance, [GFP-PAC]). Cells were transfected with replicon-derived transcript RNA and GFP fluorescence quantified. Replication of transcript RNAs was readily detected by fluorescence, whilst the signal from replication-incompetent forms of the genome was >2-fold lower. Surprisingly, a form of the replicon lacking the Lpro showed a significantly stronger fluorescence signal, but appeared with slightly delayed kinetics. Replication can, therefore, be quantified simply by live-cell imaging and image analyses, providing a rapid and facile alternative to RT-qPCR or CAT assays
Near and mid-IR sub-arcsecond structure of the dusty symbiotic star R Aqr
The results of a high-resolution interferometric campaign targeting the
symbiotic long-period variable (LPV) R~Aqr are reported. With both
near-infrared measurements on baselines out to 10m and mid-infrared data
extending to 32m, we have been able to measure the characteristic sizes of
regions from the photosphere of the LPV and its extended molecular atmosphere,
out to the cooler circumstellar dust shell. The near-infrared data were taken
using aperture masking interferometry on the Keck-I telescope and show R~Aqr to
be partially resolved for wavelengths out to 2.2 microns but with a marked
enlargement, possibly due to molecular opacity, at 3.1 microns. Mid-infrared
interferometric measurements were obtained with the U.C. Berkeley Infrared
Spatial Interferometer (ISI) operating at 11.15 microns from 1992 to 1999.
Although this dataset is somewhat heterogeneous with incomplete coverage of the
Fourier plane and sampling of the pulsation cycle, clear changes in the
mid-infrared brightness distribution were observed, both as a function of
position angle on the sky and as a function of pulsation phase. Spherically
symmetric radiative transfer calculations of uniform-outflow dust shell models
produce brightness distributions and spectra which partially explain the data,
however limitations to this approximation are noted. Evidence for significant
deviation from circular symmetry was found in the mid-infrared and more
tentatively at 3.08 microns in the near-infrared, however no clear detection of
binarity or of non-LPV elements in the symbiotic system is reported.Comment: Accepted to Astrophysical Journal. To appear in volume 534. 14 pages;
3 postscript figure
Lazarus Syndrome - Challenges created by pediatric autoresuscitation
Pediatric autoresuscitation is extremely rare, with only 4 documented cases in the literature. The longest recorded time between stopping cardio pulmonary resuscitation (CPR) and return of spontaneous circulation is 2 minutes. We report a previously well 18-month-old who attended the emergency department after an unexplained cardiac arrest. After 10 cycles of CPR, resuscitation was stopped; 6 minutes later, the patient had a return of spontaneous circulation and was transferred to the pediatric intensive care unit. The patient remains alive but with significant neurological impairment. There are a variety of theories regarding the pathology of pediatric autoresuscitation. The most commonly accepted model is that there is a degree of autopositive end-expiratory pressure impending venous return as a consequence of vigorous ventilation during CPR. This case challenges clinicians to reassess our current definition of death and reaffirms the need for clearer guidelines surrounding the certification of death
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