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  • 1
    Publication Date: 2017-10-14
    Description: The spin splitting of conduction band electrons in inversion-asymmetric InGaAs/InP quantum wells (QWs) is studied by Shubnikov-de Haas measurements combining the analysis of beating patterns and coincidence measurements in doubly tilted magnetic fields. The method allows us to determine the absolute values of the Rashba and linear Dresselhaus spin–orbit interaction (SOI) coefficients, their relative sign and the full Landé g-tensor. This is achieved by analyzing the anisotropy of the beat node positions with respect to both polar and azimuthal angles between the magnetic field direction and the QW normal. We show that the SOI is dominated by a large Rashba coefficient together with a linear Dresselhaus coefficient that is 10% of the Rashba coefficient. Their relative sign is found to be positive. The g-tensor is found to have a marked out-of-plane anisotropy and a smaller but distinct in-plane anisotropy due to SOI.
    Electronic ISSN: 1367-2630
    Topics: Physics
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  • 2
    Publication Date: 2016-01-21
    Description: RNA polymerase (Pol) II produces messenger RNA during transcription of protein-coding genes in all eukaryotic cells. The Pol II structure is known at high resolution from X-ray crystallography for two yeast species. Structural studies of mammalian Pol II, however, remain limited to low-resolution electron microscopy analysis of human Pol II and its complexes with various proteins. Here we report the 3.4 A resolution cryo-electron microscopy structure of mammalian Pol II in the form of a transcribing complex comprising DNA template and RNA transcript. We use bovine Pol II, which is identical to the human enzyme except for seven amino-acid residues. The obtained atomic model closely resembles its yeast counterpart, but also reveals unknown features. Binding of nucleic acids to the polymerase involves 'induced fit' of the mobile Pol II clamp and active centre region. DNA downstream of the transcription bubble contacts a conserved 'TPSA motif' in the jaw domain of the Pol II subunit RPB5, an interaction that is apparently already established during transcription initiation. Upstream DNA emanates from the active centre cleft at an angle of approximately 105 degrees with respect to downstream DNA. This position of upstream DNA allows for binding of the general transcription elongation factor DSIF (SPT4-SPT5) that we localize over the active centre cleft in a conserved position on the clamp domain of Pol II. Our results define the structure of mammalian Pol II in its functional state, indicate that previous crystallographic analysis of yeast Pol II is relevant for understanding gene transcription in all eukaryotes, and provide a starting point for a mechanistic analysis of human transcription.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bernecky, Carrie -- Herzog, Franz -- Baumeister, Wolfgang -- Plitzko, Jurgen M -- Cramer, Patrick -- England -- Nature. 2016 Jan 28;529(7587):551-4. doi: 10.1038/nature16482. Epub 2016 Jan 20.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Biophysical Chemistry, Department of Molecular Biology, Am Fassberg 11, 37077 Gottingen, Germany. ; Gene Center Munich, Ludwig-Maximilians-Universitat Munchen, Feodor-Lynen-Strasse 25, 81377 Munich, Germany. ; Max Planck Institute for Biochemistry, Department of Molecular Structural Biology, Am Klopferspitz 18, 82152 Martinsried, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26789250" target="_blank"〉PubMed〈/a〉
    Keywords: Allosteric Regulation ; Amino Acid Motifs ; Animals ; Catalytic Domain ; Cattle ; *Cryoelectron Microscopy ; DNA/genetics/metabolism/ultrastructure ; Humans ; Models, Molecular ; Nucleic Acids/chemistry/metabolism ; Protein Structure, Tertiary ; Protein Subunits/chemistry/metabolism ; RNA Polymerase II/chemistry/*metabolism/*ultrastructure ; RNA, Messenger/biosynthesis/genetics/ultrastructure ; Saccharomyces cerevisiae/enzymology ; Templates, Genetic ; *Transcription Elongation, Genetic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2015-02-06
    Description: The conserved co-activator complex Mediator enables regulated transcription initiation by RNA polymerase (Pol) II. Here we reconstitute an active 15-subunit core Mediator (cMed) comprising all essential Mediator subunits from Saccharomyces cerevisiae. The cryo-electron microscopic structure of cMed bound to a core initiation complex was determined at 9.7 A resolution. cMed binds Pol II around the Rpb4-Rpb7 stalk near the carboxy-terminal domain (CTD). The Mediator head module binds the Pol II dock and the TFIIB ribbon and stabilizes the initiation complex. The Mediator middle module extends to the Pol II foot with a 'plank' that may influence polymerase conformation. The Mediator subunit Med14 forms a 'beam' between the head and middle modules and connects to the tail module that is predicted to bind transcription activators located on upstream DNA. The Mediator 'arm' and 'hook' domains contribute to a 'cradle' that may position the CTD and TFIIH kinase to stimulate Pol II phosphorylation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Plaschka, C -- Lariviere, L -- Wenzeck, L -- Seizl, M -- Hemann, M -- Tegunov, D -- Petrotchenko, E V -- Borchers, C H -- Baumeister, W -- Herzog, F -- Villa, E -- Cramer, P -- England -- Nature. 2015 Feb 19;518(7539):376-80. doi: 10.1038/nature14229. Epub 2015 Feb 4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Biophysical Chemistry, Department of Molecular Biology, Am Fassberg 11, 37077 Gottingen, Germany. ; Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universitat Munchen, Feodor-Lynen-Strasse 25, 81377 Munich, Germany. ; Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany. ; Department of Biochemistry and Microbiology, Genome British Columbia Protein Centre, University of Victoria, 3101-4464 Markham Street, Victoria, British Columbia V8Z7X8, Canada. ; 1] Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany [2] Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25652824" target="_blank"〉PubMed〈/a〉
    Keywords: Allosteric Regulation ; Binding Sites ; *Cryoelectron Microscopy ; DNA/chemistry/metabolism ; Enzyme Activation ; Mediator Complex/*chemistry/metabolism/*ultrastructure ; Models, Molecular ; Phosphorylation ; Protein Stability ; Protein Structure, Tertiary ; Protein Subunits/chemistry/metabolism ; RNA Polymerase II/*chemistry/metabolism/*ultrastructure ; Saccharomyces cerevisiae/*chemistry/*ultrastructure ; Saccharomyces cerevisiae Proteins/chemistry/metabolism/ultrastructure ; Transcription Factor TFIIB/chemistry/metabolism ; Transcription Factor TFIIH/chemistry/metabolism ; Transcription Initiation, Genetic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 2017-08-01
    Print ISSN: 1126-6708
    Electronic ISSN: 1029-8479
    Topics: Physics
    Published by Springer
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  • 5
    Publication Date: 2017-12-01
    Print ISSN: 1126-6708
    Electronic ISSN: 1029-8479
    Topics: Physics
    Published by Springer
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  • 6
    Publication Date: 2017-10-01
    Print ISSN: 1126-6708
    Electronic ISSN: 1029-8479
    Topics: Physics
    Published by Springer
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  • 7
    Publication Date: 2015-07-14
    Description: We present an on-chip beamsplitter operating on a single-photon level by means of a quasi-resonantly driven InGaAs/GaAs quantum dot. The single photons are guided by rib waveguides and split into two arms by an evanescent field coupler. Although the waveguides themselves support the fundamental TE and TM modes, the measured degree of polarization (∼90%) reveals the main excitation and propagation of the TE mode. We observe the preserved single-photon nature of a quasi-resonantly excited quantum dot by performing a cross-correlation measurement on the two output arms of the beamsplitter. Additionally, the same quantum dot is investigated under resonant excitation, where the same splitting ratio is observed. An autocorrelation measurement with an off-chip beamsplitter on a single output arm reveal the single-photon nature after evanescent coupling inside the on-chip splitter. Due to their robustness, adjustable splitting ratio, and their easy implementation, rib waveguide beamsplitters with embedded quantum dots provide a promising step towards fully integrated quantum circuits.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 8
    Publication Date: 2015-07-02
    Description: The identification of crosslinks by mass spectrometry has recently been established as an integral part of the hybrid structural analysis of protein complexes and networks. The crosslinking analysis determines distance restraints between two covalently linked amino acids which are typically summarized in a table format that precludes the immediate and comprehensive interpretation of the topological data. xVis displays crosslinks in clear schematic representations in form of a circular, bar or network diagram. The interactive graphs indicate the linkage sites and identification scores, depict the spatial proximity of structurally and functionally annotated protein regions and the evolutionary conservation of amino acids and facilitate clustering of proteins into subcomplexes according to the crosslink density. Furthermore, xVis offers two options for the qualitative assessment of the crosslink identifications by filtering crosslinks according to identification scores or false discovery rates and by displaying the corresponding fragment ion spectrum of each crosslink for the manual validation of the mass spectrometric data. Our web server provides an easy-to-use tool for the fast topological and functional interpretation of distance information on protein complex architectures and for the evaluation of crosslink fragment ion spectra. xVis is available under a Creative Commons Attribution-ShareAlike 4.0 International license at http://xvis.genzentrum.lmu.de/ .
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 9
    Publication Date: 2015-09-30
    Description: Any profound comprehension of gene function requires detailed information about the subcellular localization, molecular interactions and spatio-temporal dynamics of gene products. We developed a multifunctional integrase (MIN) tag for rapid and versatile genome engineering that serves not only as a genetic entry site for the Bxb1 integrase but also as a novel epitope tag for standardized detection and precipitation. For the systematic study of epigenetic factors, including Dnmt1 , Dnmt3a , Dnmt3b , Tet1 , Tet2 , Tet3 and Uhrf1 , we generated MIN-tagged embryonic stem cell lines and created a toolbox of prefabricated modules that can be integrated via Bxb1-mediated recombination. We used these functional modules to study protein interactions and their spatio-temporal dynamics as well as gene expression and specific mutations during cellular differentiation and in response to external stimuli. Our genome engineering strategy provides a versatile open platform for efficient generation of multiple isogenic cell lines to study gene function under physiological conditions.
    Keywords: Synthetic Biology and Assembly Cloning, Targeted gene modification
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 10
    Publication Date: 2016-09-21
    Description: Cotranscriptional ubiquitination of histone H2B is key to gene regulation. The yeast E3 ubiquitin ligase Bre1 (human RNF20/40) pairs with the E2 ubiquitin conjugating enzyme Rad6 to monoubiquitinate H2B at Lys123. How this single lysine residue on the nucleosome core particle (NCP) is targeted by the Rad6–Bre1 machinery is unknown....
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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