Show Abstract ▼

Abstract: Background: Defects in the human Shwachman-Bodian-Diamond syndrome (SBDS) protein-coding gene lead to the autosomal recessive disorder characterised by bone marrow dysfunction, exocrine pancreatic insufficiency and skeletal abnormalities. This protein is highly conserved in eukaryotes and archaea but is not found in bacteria. Although genomic and biophysical studies have suggested involvement of this protein in RNA metabolism and in ribosome biogenesis, its interacting partners remain largely unknown.Results: We determined the crystal structure of the SBDS orthologue from Methanothermobacter thermautotrophicus (mthSBDS). This structure shows that SBDS proteins are highly flexible, with the N-terminal FYSH domain and the C-terminal ferredoxin-like domain capable of undergoing substantial rotational adjustments with respect to the central domain. Affinity chromatography identified several proteins from the large ribosomal subunit as possible interacting partners of mthSBDS. Moreover, SELEX (Systematic Evolution of Ligands by EXponential enrichment) experiments, combined with electrophoretic mobility shift assays (EMSA) suggest that mthSBDS does not interact with RNA molecules in a sequence specific manner.Conclusion: It is suggested that functional interactions of SBDS proteins with their partners could be facilitated by rotational adjustments of the N-terminal and the C-terminal domains with respect to the central domain. Examination of the SBDS protein structure and domain movements together with its possible interaction with large ribosomal subunit proteins suggest that these proteins could participate in ribosome function.

Show Abstract ▼

Abstract: The valence-band electronic structure of a clean Ni(111) surface is investigated by spin-resolved photoemission. At room temperature the orientation of the photoelectron spins on the Bloch sphere and the exchange splitting of surface and bulk states along the surface normal (Gamma) are determined. All investigated states are found to have a sizable exchange splitting >50 meV. Since the splitting is smaller than the intrinsic line width in the spin-integrated spectrum this is only seen with a spin-resolved technique. At room-temperature photoemission reaching above the Fermi level directly shows that the Shockley type surface state S(1) has an occupied majority and an unoccupied minority band with a splitting Delta E(ex)=62 +/- 15 meV. The surface states below the Fermi energy show a larger exchange splitting for in-plane hybridization [Delta E(ex)(S(3))=160 meV] than for out-of-plane hybridization [Delta E(ex)(S(2))=55 meV].

Show Abstract ▼

Abstract: An FePd thin film sample, showing magnetic stripe domains as imaged by magnetic force microscopy, has been measured by soft X-ray resonant magnetic scattering in reflection geometry. Illumination with coherent radiation, produced by inserting a 20 mum pinhole in front of the sample, leads to a magnetic speckle pattern in the scattered intensity that gives access to the domain morphology. Application of an in-plane magnetic field for a few seconds gives a strong change in the observed intensity fluctuations, which indicates a large degree of variation between the two patterns taken before and after field exposure. From the speckle pattern we calculate a degree of coherence of beta = 0.5 for the incident beam.

Show Abstract ▼

Abstract: The recognition of the correct substrate and rejection of the incorrect substrate by RNA-modifying enzymes is of great importance to the process of posttranscriptional base modification. Between 2001 and 2008, structures of nine different rRNA and tRNA base-modifying enzymes in complex with RNA were published and these revealed a plethora of mechanisms for substrate recognition. While some complexes appear to be the result of the RNA being bound primarily as a rigid body, a significant number of enzymes remodel the RNA upon binding, either to increase the affinity of the interaction and/or access an otherwise buried base. Pertinent examples of remodelled RNA are observed in the structures of the ArcTGT-tRNA and RlmD-rRNA complexes. In a number of RNA-modifying enzymes it is clear that there is a degree of modularity, such that the substrate specificity is partly defined by a domain(s) that recognises a particular feature in the RNA while the modification is performed by a suitably positioned catalytic domain. With this chapter we will first review the general principles of protein-RNA interactions and modularity in RNA-modifying enzymes before looking at how they are combined to define substrate specificity in a number of interesting protein-RNA complexes.

Show Abstract ▼

Abstract: Orbital ordering (OO) in the layered perovskite La0.5Sr1.5MnO4 has been investigated using the enhanced sensitivity of soft x-ray resonant diffraction at the Mn L edges. The energy dependence of an OO diffraction peak over the L2,3 edges is compared to ligand-field calculations allowing a distinction between the influences of Jahn-Teller distortions and spin correlations. The energy dependence of the diffraction peak at the Mn L1 edge is remarkably different from that observed at the Mn K edge.