The cleaved presequence is not required for import of subunit 6 of the cytochrome bc 1 complex into yeast mitochondria or assembly into the complex*

Abstract Subunit 6 of the yeast cytochrome bc 1 complex contains a 25 amino acid presequence that is not present in the mature form of the protein in the bc 1 complex. The presequence of subunit 6 is atypical of presequences responsible for targeting proteins to mitochondria. Whereas mitochondrial targeting sequences rarely contain acidic residues and typically contain basic residues that can potentially form an amphiphilic structure, the presequence of subunit 6 contains only one basic amino acid and is enriched in acidic amino acids. If the 25 amino acid presequence is deleted, subunit 6 is imported into mitochondria and assembled into the cytochrome bc 1 complex and the activity of the bc 1 complex is identical to that from a wild-type yeast strain. However, if the C-terminal 45 amino acids are truncated from the protein, subunit 6 is not present in the mitochondria and the activity of the bc 1 complex is diminished by half, identical to that of the bc 1 complex from a yeast strain in which the QCR6 gene is deleted. These results indicate that the presequence of subunit 6 is not required for targeting to mitochondria or assembly of the subunit into the bc 1 complex and that information necessary for targeting and import into mitochondria may be present in the C-terminus of the protein. z 1999 Federation of European Biochemical Societies

Nightside condensation of iron in an ultra-hot giant exoplanet

Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside.Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11 figures, 3 table

The challenge of highly curved monolithic imaging detectors

ABSTRACT In a recent optical design study of CODEX -a visible spectrograph planned for the European Extremely Large Telescope (E-ELT) -it was determined that a significant simplification of the optical design -accompanied by an improvement of the image quality -could be achieved through the application of large format (90mm square) concave spherically curved detectors with a low radius of curvature (500 to 250mm). Current assemblies of image sensors and optics rely on the optics to project a corrected image onto a flat detector. While scientific large-size CCDs (49mm square) have been produced unintentionally with a spherical radius of convex curvature of around 5m, in the past most efforts have concentrated onto flattening the light-sensitive detector silicon area as best as possible for both scientific state-of-the-art systems, as well as commercial low-cost consumer products. In some cases curved focal planes are mosaicked out of individual flat detectors, but a standard method to derive individual spherically curved large size detectors has not been demonstrated. This paper summarizes important developments in the area of curved detectors in the past and their different technical approaches mostly linked to specific thinning processes. ESO's specifications for an ongoing feasibility study are presented. First results of the latter are described with a link to theoretical and practical examinations of currently available technology to implement curved CCD and CMOS detectors for scientific applications

ASSIST ::development of a test-infrastructure for the VLT AO facility

ASSIST - The Adaptive Secondary Setup and Instrument STimulator is a test setup to verify the operation of three elements of the VLT Adaptive Optics Facility, namely the Deformable Secondary Mirror (DSM) and the two AO systems using this DSM, the AO system for the visible light integral field spectrograph MUSE (GALACSI) and the AO system for the IR wide field imager HAWK-I (GRAAL). To support the testing of these elements, ASSIST will provide both an interferometry setup for testing the DSM as well as a full atmospheric turbulence simulator and star simulator to mimic the conditions at the telescope. To test the instruments using the DSM, the output beam is matched the output beam of the VLT telescope, including the correct exit-pupil and high-quality imaging and a similar hardware interface is provided. Since one of the modes to be verified is nearly diffraction limited, also the thermal and vibrational stability are very important, with strong constraints on both the mechanical as well as the optical design

ASSIST ::the test setup for the VLT AO facility

ASSIST: The Adaptive Secondary Setup and Instrument STimulator is the test setup for the verification and calibration of three elements of the VLT Adaptive Optics Facility.; the Deformable Secondary Mirror (DSM) the AO system for MUSE and HAWK-I (GALACSI and GRAAL). In the DSM testing mode the DSM will be tested using both interferometry and fast wave front sensing. In full AO mode, ASSIST will allow testing of the AO systems under realistic atmospheric conditions and optically equivalent to the conditions on the telescope. ASSIST is nearing its final design review and in this paper we present the current optical and mechanical design of ASSIST. In this paper we highlight some of the specific aspects of ASSIST that we are developing for ASSIST

MOSAIC on the ELT : optomechanical design of the NIR spectrograph

International audienceContext. The circumgalactic medium (CGM) is the location where the interplay between large-scale outflows and accretion onto galaxies occurs. Metals in different ionization states flowing between the circumgalactic and intergalactic mediums are affected by large galactic outflows and low-ionization state inflowing gas. Observational studies on their spatial distribution and their relation with galaxy properties may provide important constraints on models of galaxy formation and evolution. Aims. The main goal of this paper is to provide new insights into the spatial distribution of the circumgalactic of star-forming galaxies at 1.5  1.5) and stellar mass (log[ M ⋆ / M ⊙ ] > 10.2) show stronger C IV absorptions compared with those low SFR (log[SFR/( M ⊙ yr −1 )] < 0.9) and low stellar mass (log[ M ⋆ / M ⊙ ] < 9.26). The latter population instead shows stronger C II absorption than their more massive or more star-forming counterparts. We compute the C II /C IV W 0 line ratio that confirms the C II and C IV correlations with impact parameter, stellar mass, and star formation rate. We do not find any correlation with ϕ in agreement with other high-redshift studies and in contradiction to what is observed at low redshift where large-scale outflows along the minor axis forming bipolar outflows are detected. Conclusions. We find that the stronger C IV line absorptions in the outer regions of these star-forming galaxies could be explained by stronger outflows in galaxies with higher star formation rates and stellar masses that are capable of projecting the ionized gas up to large distances and/or by stronger UV ionizing radiation in these galaxies that is able to ionize the gas even at large distances. On the other hand, low-mass galaxies show stronger C II absorptions, suggesting larger reservoirs of cold gas that could be explained by a softer radiation field unable to ionize high-ionization state lines or by the galactic fountain scenario where metal-rich gas ejected from previous star formation episodes falls back to the galaxy. These large reservoirs of cold neutral gas around low-mass galaxies could be funnelled into the galaxies and eventually provide the necessary fuel to sustain star formation activity