About Schmidt

This is a review of About Schmidt (2002)

Pat1 RNA-binding proteins: Multitasking shuttling proteins.

Post-transcriptional regulation of gene expression is largely achieved at the level of splicing in the nucleus, and translation and mRNA decay in the cytosol. While the regulation may be global, through the direct inhibition of central factors, such as the spliceosome, translation initiation factors and mRNA decay enzymes, in many instances transcripts bearing specific sequences or particular features are regulated by RNA-binding factors which mobilize or impede recruitment of these machineries. This review focuses on the Pat1 family of RNA-binding proteins, conserved from yeast to man, that enhance the removal of the 5' cap by the decapping enzyme Dcp1/2, leading to mRNA decay and also have roles in translational repression. Like Dcp1/2, other decapping coactivators, including DDX6 and Edc3, and translational repressor proteins, Pat1 proteins are enriched in cytoplasmic P-bodies, which have a principal role in mRNA storage. They also concentrate in nuclear Cajal-bodies and splicing speckles and in man, impact splice site choice in some pre-mRNAs. Pivotal to these functions is the association of Pat1 proteins with distinct heptameric Lsm complexes: the cytosolic Pat1/Lsm1-7 complex mediates mRNA decay and the nuclear Pat1/Lsm2-8 complex alternative splicing. This dual role of human Pat1b illustrates the power of paralogous complexes to impact distinct processes in separate compartments. The review highlights our recent findings that Pat1b mediates the decay of AU-rich mRNAs, which are particularly enriched in P-bodies, unlike the decapping activator DDX6, which acts on GC-rich mRNAs, that tend to be excluded from P-bodies, and discuss the implications for mRNA decay pathways. This article is categorized under: RNA Turnover and Surveillance > Regulation of RNA Stability RNRNA Processing > Splicing Regulation/Alternative Splicing Translation > Translation Regulation.This work was supported by the BBSRC, Newton Trust and Foundation Wiener – Anspach (C.V.) to N.S.’s laboratory, and the Association pour la Recherche sur le Cancer and the Agence Nationale pour la Recherche contract ANR-14-CE09-0013-01 to D.W.’s laboratory

The yellow hypergiants HR 8752 and rho Cassiopeiae near the evolutionary border of instability

High-resolution near-ultraviolet spectra of the yellow hypergiants HR 8752 and rho Cassiopeiae indicate high effective temperatures placing both stars near the T_eff border of the ``yellow evolutionary void''. At present, the temperature of HR 8752 is higher than ever. For this star we found Teff=7900+-200 K, whereas rho Cassiopeiae has Teff=7300+-200 K. Both, HR 8752 and rho Cassiopeiae have developed strong stellar winds with Vinf ~ 120 km/s and Vinf ~ 100 km/s, respectively. For HR 8752 we estimate an upper limit for the spherically symmetric mass-loss of 6.7X10^{-6}M_solar/yr. Over the past decades two yellow hypergiants appear to have approached an evolutionary phase, which has never been observed before. We present the first spectroscopic evidence of the blueward motion of a cool super/hypergiant on the HR diagram.Comment: 13 pages including 3 figures. Accepted for publication in ApJ Letter

FUSE Observations of the Dwarf Nova SW UMa During Quiescence

We present spectroscopic observations of the short-period cataclysmic variable SW Ursa Majoris, obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite while the system was in quiescence. The data include the resonance lines of O VI at 1031.91 and 1037.61 A. These lines are present in emission, and they exhibit both narrow (~ 150 km/s) and broad (~ 2000 km/s) components. The narrow O VI emission lines exhibit unusual double-peaked and redshifted profiles. We attribute the source of this emission to a cooling flow onto the surface of the white dwarf primary. The broad O VI emission most likely originates in a thin, photoionized surface layer on the accretion disk. We searched for emission from H_2 at 1050 and 1100 A, motivated by the expectation that the bulk of the quiescent accretion disk is in the form of cool, molecular gas. If H_2 is present, then our limits on the fluxes of the H_2 lines are consistent with the presence of a surface layer of atomic H that shields the interior of the disk. These results may indicate that accretion operates primarily in the surface layers of the disk in SW UMa. We also investigate the far-UV continuum of SW UMa and place an upper limit of 15,000 K on the effective temperature of the white dwarf.Comment: 21 Pages, 3 figures, to be published in Ap

A Binary Orbit for the Massive, Evolved Star HDE 326823, a WR+O System Progenitor

The hot star HDE 326823 is a candidate transition-phase object that is evolving into a nitrogen-enriched Wolf-Rayet star. It is also a known low-amplitude, photometric variable with a 6.123 d period. We present new, high and moderate resolution spectroscopy of HDE 326823, and we show that the absorption lines show coherent Doppler shifts with this period while the emission lines display little or no velocity variation. We interpret the absorption line shifts as the orbital motion of the apparently brighter star in a close, interacting binary. We argue that this star is losing mass to a mass gainer star hidden in a thick accretion torus and to a circumbinary disk that is the source of the emission lines. HDE 326823 probably belongs to a class of objects that produce short-period WR+O binaries.Comment: 32 pages, 10 figures, accepted to the Astronomical Journa

Imaging the dynamical atmosphere of the red supergiant Betelgeuse in the CO first overtone lines with VLTI/AMBER

We present the first 1-D aperture synthesis imaging of the red supergiant Betelgeuse in the individual CO first overtone lines with VLTI/AMBER. The reconstructed 1-D projection images reveal that the star appears differently in the blue wing, line center, and red wing of the individual CO lines. The 1-D projection images in the blue wing and line center show a pronounced, asymmetrically extended component up to ~1.3 stellar radii, while those in the red wing do not show such a component. The observed 1-D projection images in the lines can be reasonably explained by a model in which the CO gas within a region more than half as large as the stellar size is moving slightly outward with 0--5 km s^-1, while the gas in the remaining region is infalling fast with 20--30 km s^-1. A comparison between the CO line AMBER data taken in 2008 and 2009 shows a significant time variation in the dynamics of the CO line-forming region in the photosphere and the outer atmosphere. In contrast to the line data, the reconstructed 1-D projection images in the continuum show only a slight deviation from a uniform disk or limb-darkened disk. We derive a uniform-disk diameter of 42.05 +/- 0.05 mas and a power-law-type limb-darkened disk diameter of 42.49 +/- 0.06 mas and a limb-darkening parameter of (9.7 +/- 0.5) x 10^{-2}. This latter angular diameter leads to an effective temperature of 3690 +/- 54 K for the continuum-forming layer. These diameters confirm that the near-IR size of Betelgeuse was nearly constant over the last 18 years, in marked contrast to the recently reported noticeable decrease in the mid-IR size. The continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulations.Comment: 21 pages, 12 figures, accepted for publication in Astronomy and Astrophysic

On the CO Near-IR Band and the Line Splitting Phenomenon in the Yellow Hypergiant Rho Cassiopeiae

We report on multi-epoch optical and near-infrared spectroscopy around the first overtone ro-vibrational band of CO in the pulsating yellow hypergiant Rho Cas, one of the most massive stars in the Galaxy and a candidate SN II progenitor. We argue that the double cores of the CO absorption lines, that have previously been attributed to separate circumstellar shells expelled during its recurrent outbursts, result in fact from a superposition of a wide absorption line and a narrow central emission line. The CO line doubling returns over subsequent pulsation cycles, where the superposed line emission assumes its largest intensity near phases of maximum light. We find that the morphology and behavior of the CO band closely resemble the remarkable "line-splitting phenomenon" also observed in optical low-excitation atomic lines. Based on radiative transport calculations we present a simplified model of the near-IR CO emission emerging from cooler atmospheric layers in the immediate vicinity of the photosphere. We speculate that the kinetic temperature minimum in our model results from a periodical pulsation-driven shock wave. We further discuss a number of alternative explanations for the origin of the ubiquitous emission line spectrum, possibly due to a quasi-chromosphere or a steady shock wave at the interface of a fast expanding wind and the ISM. We present a number of interesting spectroscopic similarities between Rho Cas and other types of cool variable supergiants such as the RV Tau and R CrB stars. We further propose a possibly common mechanism for the enigmatic outburst behavior of these luminous pulsating cool stars.Comment: accepted to ApJ; 3 color fig

Tunable Depletion Potentials Driven By Shape Variation Of Surfactant Micelles

Depletion interaction potentials between micron-sized colloidal particles are induced by nanometer-scale surfactant micelles composed of hexaethylene glycol monododecyl ether (C12E6), and they are measured by video microscopy. The strength and range of the depletion interaction is revealed to arise from variations in shape anisotropy of the surfactant micelles. This shape anisotropy increases with increasing sample temperature. By fitting the colloidal interaction potentials to theoretical models, we extract micelle length and shape anisotropy as a function of temperature. This work introduces shape anisotropy tuning as a means to control interparticle interactions in colloidal suspensions, and it shows how the interparticle depletion potentials of micron-scale objects can be employed to probe the shape and size of surrounding macromolecules at the nanoscale