49 research outputs found
A low background Micromegas detector for the CAST experiment
A low background Micromegas detector has been operating on the CAST
experiment at CERN for the search of solar axions during the first phase of the
experiment (2002-2004). The detector operated efficiently and achieved a very
low level of background rejection ( counts
keVcms) thanks to its good spatial and energy resolution
as well as the low radioactivity materials used in the construction of the
detector. For the second phase of the experiment (2005-2007), the detector will
be upgraded by adding a shielding and including focusing optics. These
improvements should allow for a background rejection better than two orders of
magnitude.Comment: 6 pages, 3 figures To appear on the proceedings of the 9th ICATPP
Conference on AStroparticle, Particle, Space Physics, Detectors and Medical
Physics Application
Nucleic Acids Res
The HIV-1 nucleocapsid protein (NCp7) is a nucleic acid chaperone required during reverse transcription. During the first strand transfer, NCp7 is thought to destabilize cTAR, the (-)DNA copy of the TAR RNA hairpin, and subsequently direct the TAR/cTAR annealing through the zipping of their destabilized stem ends. To further characterize the destabilizing activity of NCp7, we locally probe the structure and dynamics of cTAR by steady-state and time resolved fluorescence spectroscopy. NC(11-55), a truncated NCp7 version corresponding to its zinc-finger domain, was found to bind all over the sequence and to preferentially destabilize the penultimate double-stranded segment in the lower part of the cTAR stem. This destabilization is achieved through zinc-finger-dependent binding of NC to the G(10) and G(50) residues. Sequence comparison further revealed that C*A mismatches close to the two G residues were critical for fine tuning the stability of the lower part of the cTAR stem and conferring to G(10) and G(50) the appropriate mobility and accessibility for specific recognition by NC. Our data also highlight the necessary plasticity of NCp7 to adapt to the sequence and structure variability of cTAR to chaperone its annealing with TAR through a specific pathway
Studying membrane properties using Fluorescence Lifetime Imaging Microscopy (FLIM)
Fluorescence lifetime imaging microscopy (FLIM) is a powerful tool to investigate the structure and composition of biological membranes. A wide variety of fluorescent probes suitable for FLIM experiments have been described. These compounds differ strongly in the details of their incorporation into membranes and in their responses toward changes in the membrane composition. In this chapter, we discuss and compare different classes of fluorescent membranes probes and their applications to studying biological membranes. We devote a section to a detailed description of fluorescent molecular rotors and their application to measuring local viscosity. As Förster resonance energy transfer (FRET) can be directly measured by changes in the donor fluorescence lifetime, FLIM is a very robust method to determine the distances between FRET pairs or the local concentrations of FRET-based membrane probes. Thus, we also discuss advantages and challenges of FRET-FLIM in the context of biological membranes. As biological membranes are considerably dynamic systems, imaging speed is often the limiting factor in biological FLIM experiments. Thus, novel fast imaging approaches and analysis methods to alleviate the issue of low photon statistics are also presented
A triterpene oleanolic acid conjugate with 3-hydroxyflavone derivative as a new membrane probe with two-color ratiometric response
We report on the synthesis by coupling of a triterpenoid oleanolic acid with 4'-diethylamino-3-hydroxyflavone (FE) to produce an environment-sensitive biomembrane probe with two-band ratiometric response in fluorescence emission. The synthesized compound (probe FOT) was tested in a series of model solvents and demonstrated the response to solvent polarity and intermolecular hydrogen bonding very similar to that of parent probe FE. Meantime when incorporated into lipid bilayer membranes, it showed new features differing in response between lipids of different surface charges as well as between glycerophospholipids and sphingomyelin
Lactose-ornithine bolaamphiphiles for efficient gene delivery in vitro.
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TNF receptor membrane dynamics studied with fluorescence microscopy and spectroscopy
Neugart F, Widera D, Kaltschmidt B, Kaltschmidt C, Heilemann M. TNF receptor membrane dynamics studied with fluorescence microscopy and spectroscopy. In: Mely Y, Duportail <G, eds. Fluorescent Methods to Study Biological Membranes. Springer Series on Fluorescence. Berlin, Heidelberg: Springer; 2012: 439-457
Synthesis and fluorescence properties of novel transmembrane probes and determination of their orientation within vesicles
Two novel transmembrane fluorescent diester probes D and E bearing an anthracenediyl moiety in the middle of the molecule have been synthesized. Their absorption and fluorescence spectra in CHCl3 solution as well as their fluorescence characteristics in dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles were determined. Although their absorption spectra (first transition, S-0 --> S-1) present a good overlap with the fluorescence spectrum of tryptophan, only probe E could be a good acceptor for the energy-transfer experiments, since a strong overlap exists between the absorption spectrum of tryptophan and the second transition (S-0 --> S-2) of the absorption spectrum of probe D. The Forster critical distance R-0 for energy transfer between tryptophan (donor) and probe E (acceptor) is found to be 23-24 Angstrom. Finally, linear-dichroism studies on shear-deformed DMPC vesicles show the incorporated probe E to lie essentially perpendicular to the bilayer plane. These results establish that probe E could be useful in the study of membrane-bound protein topography by the fluorescence-energy-transfer method