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Abstract: Although structural studies on the ligand-binding domain (LBD) have established the general mode of nuclear receptor (NR)/coactivator interaction, determinants of binding specificity are only partially understood. The LBD of estrogen receptor-? (ER?), for example, interacts only with a region of peroxisome proliferator-activated receptor coactivator (PGC)-1?, which contains the canonical LXXLL motif (NR box2), whereas the LBD of estrogen-related receptor-? (ERR?) also binds efficiently an untypical, LXXYL-containing region (NR box3) of PGC-1?. Surprisingly, in a previous structural study, the ER? LBD has been observed to bind NR box3 of transcriptional intermediary factor (TIF)-2 untypically via LXXYL, whereas the ERR? LBD binds this region of TIF-2 only poorly. Here we present a new crystal structure of the ERR? LBD in complex with a PGC-1? box3 peptide. In this structure, residues N-terminal of the PGC-1? LXXYL motif formed contacts with helix 4, the loop connecting helices 8 and 9, and with the C terminus of the ERR? LBD. Interaction studies using wild-type and mutant PGC-1? and ERR? showed that these contacts are functionally relevant and are required for efficient ERR?/PGC-1? interaction. Furthermore, a structure comparison between ERR? and ER? and mutation analyses provided evidence that the helix 8–9 loop, which differs significantly in both nuclear receptors, is a major determinant of coactivator binding specificity. Finally, our results revealed that in ERR? the helix 8–9 loop allosterically links the LBD homodimer interface with the coactivator cleft, thus providing a plausible explanation for distinct PGC-1? binding to ERR? monomers and homodimers.

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Abstract: We report a sequent phase transition using high-resolution synchrotron x-ray scattering in a single crystalNd 1/2 Sr 1/2 MnO 3 . By measuring the peak profile of Bragg reflections, upon cooling, we observed an increase in the width of the Bragg reflections around the Curie temperature (252 K) corresponding to the transition from a paramagnetic to a ferromagnetic state. Below approximately 200 K, dramatic changes in the width and integrated intensity were observed. Changes continued until the formation of charge ordering with q=(12 ,0,0) at T CO =152?K . This charge ordering was observed to be the first order transition with a large hysteresis width of 10 K. This sequent transition is understood by the formation of different magnetic domains at different temperature ranges as that observed by neutronpowderdiffraction.

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Abstract: Soft X-ray resonant magnetic scattering offers a unique element-, site- and valence- specific probe to study magnetic structures on the nanoscopic length scale. This new technique, which combines X-ray scattering with X-ray magnetic circular and linear dichroism, is ideally suited to investigate magnetic superlattices and magnetic domain structures. The theoretical analysis of the polarization dependence to determine the vector magnetization profile is presented. This is illustrated with examples studying the closure domains in self-organising magnetic domain structures, the magnetic order in patterned samples, and the local configuration of magnetic nano-objects using coherent X-rays.

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Abstract: The FACT complex is a conserved cofactor for RNA polymerase II elongation through nucleosomes. FACT bears histone chaperone activity and contributes to chromatin integrity. However, the molecular mechanisms behind FACT function remain elusive. Here we report biochemical, structural, and mutational analyses that identify the peptidase homology domain of the Schizosaccharomyces pombe FACT large subunit Spt16 (Spt16-N) as a binding module for histones H3 and H4. The 2.1-Å crystal structure of Spt16-N reveals an aminopeptidase P fold whose enzymatic activity has been lost. Instead, the highly conserved fold directly binds histones H3–H4 through a tight interaction with their globular core domains, as well as with their N-terminal tails. Mutations within a conserved surface pocket in Spt16-N or posttranslational modification of the histone H4 tail reduce interaction in vitro, whereas the globular domains of H3–H4 and the H3 tail bind distinct Spt16-N surfaces. Our analysis suggests that the N-terminal domain of Spt16 may add to the known H2A–H2B chaperone activity of FACT by including a H3–H4 tail and H3–H4 core binding function mediated by the N terminus of Spt16. We suggest that these interactions may aid FACT-mediated nucleosome reorganization events.

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Abstract: The commensurate phase of multiferroic HoMn 2 O 5 was studied by x-ray magnetic scattering, both off-resonance and in resonant conditions at the Ho?L 3 edge. Below 40 K, magnetic ordering at the Ho sites is induced by the main Mn magnetic order parameter, and its temperature dependence is well accounted for by a simple Curie–Weiss susceptibility model. A lattice distortion of periodicity twice that of the magnetic order is also evidenced. The azimuthal scans confirm the model of the magnetic structure recently refined from neutron diffraction data for both Mn and Ho sites, indicating that the two sublattices interact via magnetic superexchange.