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- Akke, Magnus, et al.
(författare)
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Measurements of the frequency-dependent impedance of a thin wire with ground return
- 2005
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Ingår i: IEEE Transactions on Power Delivery. - 1937-4208. ; 20:2, s. 1748-1752
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the frequency-dependent impedance of a thin wire with ground return is performed. We argue that the results from a downscaled experimental setup are useful and relevant for power-line applications. The experimental result is compared with two categories of line models. The first category is a model that uses fixed line parameters and the second category consists of models where the inductance and the resistance are frequency dependent. As expected, the frequency-dependent line parameters must be used in the modeling for consistency with the measurements. The result shows that measurements are important to determine the accuracy and limitations of different simulation models.
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- Grela, Przemysłw, et al.
(författare)
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Structural characterization of the ribosomal P1A-P2B protein dimer by small-angle X-ray scattering and NMR spectroscopy
- 2007
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 46:7, s. 1988-1998
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Tidskriftsartikel (refereegranskat)abstract
- The five ribosomal P-proteins, denoted P0-(P1-P2)(2), constitute the stalk structure of the large subunit of eukaryotic ribosomes. In the yeast Saccharomyces cerevisiae, the group of P1 and P2 proteins is differentiated into subgroups that form two separate P1A-P2B and P1B-P2A heterodimers on the stalk. So far, structural studies on the P-proteins have not yielded any satisfactory information using either X-ray crystallography or NMR spectroscopy, and the structures of the ribosomal stalk and its individual constituents remain obscure. Here we outline a first, coarse-grained view of the P1A-P2B solution structure obtained by a combination of small-angle X-ray scattering and heteronuclear NMR spectroscopy. The complex has an elongated shape with a length of 10 nm and a cross section of similar to 2.5 nm. N-15 NMR relaxation measurements establish that roughly 30% of the residues are present in highly flexible segments, which belong primarily to the linker region and the C-terminal part of the polypeptide chain. Secondary structure predictions and NMR chemical shift analysis, together with previous results from CD spectroscopy, indicate that the structured regions involve alpha-helices. NMR relaxation data further suggest that several helices are arranged in a nearly parallel or antiparallel topology. These results provide the first structural comparison between eukaryotic P1 and P2 proteins and the prokaryotic L12 counterpart, revealing considerable differences in their overall shapes, despite similar functional roles and similar oligomeric arrangements. These results present for the first time a view of the structure of the eukaryotic stalk constituents, which is the only domain of the eukaryotic ribosome that has escaped successful structural characterization.
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- Helgstrand, Magnus, et al.
(författare)
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The ribosomal stalk binds to translation factors IF2, EF-Tu, EF-G and RF3 via a conserved region of the L12 C-terminal domain
- 2007
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 365:2, s. 468-479
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Tidskriftsartikel (refereegranskat)abstract
- Efficient protein synthesis in bacteria requires initiation factor 2 (IF2), elongation factors Tu (EF-Tu) and G (EF-G), and release factor 3 (RF3), each of which catalyzes a major step of translation in a GTP-dependent fashion. Previous reports have suggested that recruitment of factors to the ribosome and subsequent GTP hydrolysis involve the dimeric protein L12, which forms a flexible "stalk" on the ribosome. Using heteronuclear NMR spectroscopy we demonstrate that L12 binds directly to the factors IF2, EF-Tu, EF-G, and RF3 from Escherichia coli, and map the region of L12 involved in these interactions. Factor-dependent chemical shift changes show that all four factors bind to the same region of the C-terminal domain of L12. This region includes three strictly conserved residues, K70, L80, and E82, and a set of highly conserved residues, including V66, A67, V68 and G79. Upon factor binding, all NMR signals from the C-terminal domain become broadened beyond detection, while those from the N-terminal domain are virtually unaffected, implying that the C-terminal domain binds to the factor, while the N-terminal domain dimer retains its rotational freedom mediated by the flexible hinge between the two domains. Factor-dependent variations in linewidths further reveal that L12 binds to each factor with a dissociation constant in the millimolar range in solution. These results indicate that the L12-factor complexes will be highly populated on the ribosome, because of the high local concentration of ribosome-bound factor with respect to L12.
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